A phylogenomic and comparative genomic framework for resolving the polyphyly of the genus Bacillus: Proposal for six new genera of Bacillus species, Peribacillus gen. nov., Cytobacillus gen. nov., Mesobacillus gen. nov., Neobacillus gen. nov., Metabacillus gen. nov. and Alkalihalobacillus gen. nov

Agricultural Biotechnological Potential of Bacillus velezensis C3-3 and Cytobacillus sp. T106 from Resource Islands of a Semi-arid Zone of La Guajira-Colombia

Resource islands are vegetative formations in arid and semi-arid ecosystems that harbor microorganisms facing extreme conditions. However, there is a limitation in the knowledge of the agricultural biotechnological potential of microorganisms present in these islands. This study aimed to determine the capacity of Bacillus velezensis C3-3 and Cytobacillus sp. T106 isolates from resource islands to promote plant growth and control the phytopathogen Rhizoctonia solani. The bacteria were sequenced, and both grew at 50 °C, resisted 5% NaCl, withstood UV exposure, and grew in extreme pH conditions. Sixty-six genes in C3-3 and 71 in T106 were identified associated with plant growth promotion, and C3-3 was shown to promote leaf growth in lettuce plants. This promotional effect was associated with the production of indole-3-acetic acid (IAA), phosphorus solubilization, and the presence of genes related to the assimilation of rhizosphere exudates. Both strains inhibited R. solani through the production of volatile compounds and antagonism. Forty-five and 40 of these genes in C3-3 and T106, respectively, were associated with the production of proteases, lipases, siderophores, antimicrobial compounds, degradation enzymes, and secretion systems. Notably, Cytobacillus sp. has not been previously reported as a biocontrol agent. This work contributes to the evidence of the biotechnological potential of semi-arid region bacteria, offering prospects for improving agricultural production in areas with limiting conditions.

Phylogenomic and molecular marker based studies to clarify the evolutionary relationships amongst Anoxybacillus species and demarcation of the family Anoxybacillaceae and some of its constituent genera

The family Anoxybacillaceae was recently proposed encompassing the genera Anoxybacillus, Geobacillus, Parageobacillus, Saccharococcus and Thermolongibacillus. Of these genera, Anoxybacillus contains >50% of the Anoxybacillaceae species. However, Anoxybacillus species form multiple unrelated clades in phylogenetic trees and their evolutionary relationships are unclear. To clarify the evolutionary relationships of Anoxybacillus and other Anoxybacillaceae species, detailed phylogenomic and comparative analyses were conducted on 38 Anoxybacillaceae species with available genomes. In a phylogenomic tree based on 1148 core proteins, all Anoxybacillus, Geobacillus, Parageobacillus, Saccharococcus and Thermolongibacillus species, excepting Anoxybacillus sediminis, formed a strongly supported clade representing the family Anoxybacillaceae. Five conserved signature indels (CSIs) reported here are also uniquely found in these species, providing robust means for the demarcation of family Anoxybacillaceae in molecular terms. In our phylogenomic tree and in the Genomic Taxonomy Database, Anoxybacillus species formed four distinct clades designated as Anoxybacillus sensu stricto (containing the type species A. pushchinoensis), Anoxybacillus_A, Anoxybacillus_B and Anoxybacillus_C. Our analyses have identified 17 novel CSIs which offer means to reliably distinguish species from these clades based upon multiple uniquely shared molecular characteristics. Additionally, we have identified three and seven CSIs specific for the genera Geobacillus and Brevibacillus, respectively. All seven Brevibacillus-specific CSIs are also shared by Anoxybacillus sediminis, which branches reliably with this genus. Based on the strong phylogenetic and molecular evidence presented here, we are proposing that the genus Anoxybacillus should be restricted to only the species from Anoxybacillus sensu stricto clade, whereas the species from Anoxybacillus_A, Anoxybacillus_B, and Anoxybacillus_C clades should be transferred into three novel genera Anoxybacteroides gen. nov., Paranoxybacillus gen. nov. and Thermaerobacillus gen. nov., respectively. Additionally, we are also proposing the transfer of Anoxybacillus sediminis to the genus Brevibacillus. The proposed changes, which reliably depict the evolutionary relationships among Anoxybacillaceae species, should be helpful in the studies of these organisms.

Comparative Genomic and Functional Analysis of c-di-GMP Metabolism and Regulatory Proteins in Bacillus velezensis LQ-3

Bacillus velezensis is a promising candidate for biocontrol applications. A common second messenger molecule, bis-(3,5)-cyclic-dimeric-guanosine monophosphate (c-di-GMP), has the ability to regulate a range of physiological functions that impact the effectiveness of biocontrol. However, the status of the c-di-GMP signaling pathway in biocontrol strain LQ-3 remains unknown. Strain LQ-3, which was isolated from wheat rhizosphere soil, has shown effective control of wheat sharp eyespot and has been identified as B. velezensis through whole-genome sequencing analyses. In this study, we investigated the intracellular c-di-GMP signaling pathway of LQ-3 and further performed a comparative genomic analysis of LQ-3 and 29 other B. velezensis strains. The results revealed the presence of four proteins containing the GGDEF domain, which is the conserved domain for c-di-GMP synthesis enzymes. Additionally, two proteins were identified with the EAL domain, which represents the conserved domain for c-di-GMP degradation enzymes. Furthermore, one protein was found to possess a PilZ domain, indicative of the conserved domain for c-di-GMP receptors in LQ-3. These proteins are called DgcK, DgcP, YybT, YdaK, PdeH, YkuI, and DgrA, respectively; they are distributed in a similar manner across the strains and belong to the signal transduction family. We selected five genes from the aforementioned seven genes for further study, excluding YybT and DgrA. They all play a role in regulating the motility, biofilm formation, and colonization of LQ-3. This study reveals the c-di-GMP signaling pathway associated with biocontrol features in B. velezensis LQ-3, providing guidance for the prevention and control of wheat sharp eyespot by LQ-3.

The Biotechnological Potential of Plant Growth-Promoting Rhizobacteria Isolated from Maize (Zea mays L.) Cultivations in the San Martin Region, Peru

Maize (Zea mays L.) is an essential commodity for global food security and the agricultural economy, particularly in regions such as San Martin, Peru. This study investigated the plant growth-promoting characteristics of native rhizobacteria isolated from maize crops in the San Martin region of Peru with the aim of identifying microorganisms with biotechnological potential. Soil and root samples were collected from maize plants in four productive zones in the region: Lamas, El Dorado, Picota, and Bellavista. The potential of twelve bacterial isolates was evaluated through traits, such as biological nitrogen fixation, indole acetic acid (IAA) production, phosphate solubilization, and siderophore production, and a completely randomized design was used for these assays. A completely randomized block design was employed to assess the effects of bacterial strains and nitrogen doses on maize seedlings. The B3, B5, and NSM3 strains, as well as maize seeds of the yellow hard 'Advanta 9139' variety, were used in this experiment. Two of these isolates, B5 and NSM3, exhibited outstanding characteristics as plant growth promoters; these strains were capable of nitrogen fixation, IAA production (35.65 and 26.94 µg mL-1, respectively), phosphate solubilization (233.91 and 193.31 µg mL-1, respectively), and siderophore production (34.05 and 89.19%, respectively). Furthermore, molecular sequencing identified the NSM3 isolate as belonging to Sporosarcina sp. NSM3 OP861656, while the B5 isolate was identified as Peribacillus sp. B5 OP861655. These strains show promising potential for future use as biofertilizers, which could promote more sustainable agricultural practices in the region.

[Identification and antifungal activity of halophilic bacteria isolated from saline soils in Campeche, México]

Phytopathogenic fungi Alternaria alternata and Colletotrichum gloeosporioides cause diseases in plant tissues as well as significant postharvest losses. The use of chemical fungicides for their control has negative effects on health and the environment. Secondary metabolites from halophilic bacteria are a promising alternative for new antifungal compounds. In the present study, halophilic bacteria were isolated and characterized from two sites with saline soils called branquizales in Campeche, Mexico. A total of 64 bacteria were isolated. Agrobacterium, Bacillus, Inquilinus, Gracilibacillus, Metabacillus, Neobacillus, Paenibacillus, Priestia, Staphylococcus, Streptomyces and Virgibacillus were among the identified genera. The antifungal potential of the culture supernatant (CS) of 39 halophilic bacteria was investigated against C. gloeosporioides and A. alternata. The bacteria showing the greatest inhibition of mycelial growth corresponded to Bacillus subtilis CPO 4292, Metabacillus sp. CPO 4266, Bacillus sp. CPO 4295 and Bacillus sp. CPO 4279. The CS of Bacillus sp. CPO 4279 exhibited the highest activity and its ethyl acetate extract (AcOEt) inhibited the germination of C. gloeosporioides, with IC50 values of 8,630μg/ml and IC90 of 10,720μg/ml. The organic partition of the AcOEt extract led to three fractions, with acetonitrile (FAcB9) showing the highest antifungal activity, with values exceeding 66%. Halophilic bacteria from 'blanquizales' soils of the genus Bacillus sp. produce metabolites with antifungal properties that inhibit the phytopathogenic fungus C. gloeosporioides.

Novel Bacillus and Prestia isolates from Dwarf century plant enhance crop yield and salinity tolerance

Soil salinity is a major environmental stressor impacting global food production. Staple crops like wheat experience significant yield losses in saline environments. Bioprospecting for beneficial microbes associated with stress-resistant plants offers a promising strategy for sustainable agriculture. We isolated two novel endophytic bacteria, Bacillus cereus (ADJ1) and Priestia aryabhattai (ADJ6), from Agave desmettiana Jacobi. Both strains displayed potent plant growth-promoting (PGP) traits, such as producing high amounts of indole-3-acetic acid (9.46, 10.00 µgml-1), ammonia (64.67, 108.97 µmol ml-1), zinc solubilization (Index of 3.33, 4.22, respectively), ACC deaminase production and biofilm formation. ADJ6 additionally showed inorganic phosphate solubilization (PSI of 2.77), atmospheric nitrogen fixation, and hydrogen cyanide production. Wheat seeds primed with these endophytes exhibited enhanced germination, improved growth profiles, and significantly increased yields in field trials. Notably, both ADJ1 and ADJ6 tolerated high salinity (up to 1.03 M) and significantly improved wheat germination and seedling growth under saline stress, acting both independently and synergistically. This study reveals promising stress-tolerance traits within endophytic bacteria from A. desmettiana. Exploiting such under-explored plant microbiomes offers a sustainable approach to developing salt-tolerant crops, mitigating the impact of climate change-induced salinization on global food security.

Culture-dependent identification of rare marine sediment bacteria from the Gulf of Mexico and Antarctica

Laboratory-viable cultivars of previously uncultured bacteria further taxonomic understanding. Despite many years of modern microbiological investigations, the vast majority of bacterial taxonomy remains uncharacterized. While many attempts have been made to decrease this knowledge gap, culture-based approaches parse away at the unknown and are critical for improvement of both culturing techniques and computational prediction efficacy. To this end of providing culture-based approaches, we present a multi-faceted approach to recovering marine environmental bacteria. We employ combinations of nutritional availability, inoculation techniques, and incubation parameters in our recovery of marine sediment-associated bacteria from the Gulf of Mexico and Antarctica. The recovered biodiversity spans several taxa, with 16S-ITS-23S rRNA gene-based identification of multiple isolates belonging to rarer genera increasingly undergoing phylogenetic rearrangements. Our modifications to traditional culturing techniques have not only recovered rarer taxa, but also resulted in the recovery of biotechnologically promising bacteria. Together, we propose our stepwise combinations of recovery parameters as a viable approach to decreasing the bacterial knowledge gap.

Solid-State Fermented Plant Foods as New Protein Sources

The current animal-based production of protein-rich foods is unsustainable, especially in light of continued population growth. New alternative proteinaceous foods are therefore required. Solid-state fermented plant foods from Africa and Asia include several mold- and Bacillus-fermented foods such as tempeh, sufu, and natto. These fermentations improve the protein digestibility of the plant food materials while also creating unique textures, flavors, and taste sensations. Understanding the nature of these transformations is of crucial interest to inspire the development of new plant-protein foods. In this review, we describe the conversions taking place in the plant food matrix as a result of these solid-state fermentations. We also summarize how these (nonlactic) plant food fermentations can lead to desirable flavor properties, such as kokumi and umami sensations, and improve the protein quality by removing antinutritional factors and producing additional essential amino acids in these foods.

Carbonate precipitation and phosphate trapping by microbialite isolates from an alkaline insular lake (Bagno dell'Acqua, Pantelleria Island, Italy)

The Bagno dell'Acqua lake is characterized by CO2 emissions, alkaline waters (pH = 9) and Eh values which indicate strongly oxidizing conditions. A typical feature of the lake is the presence of actively growing microbialites rich in calcium carbonates and silica precipitates. Mineralogy, petrography and morphology analyses of the microbialites were coupled with the analysis of the microbial community, combining molecular and cultivation approaches. The DNA sequencing revealed distinct patterns of microbial diversity, showing pronounced differences between emerged and submerged microbialite, with the upper layer of emerged samples exhibiting the most distinctive composition, both in terms of prokaryotes and eukaryotes. In particular, the most representative phyla in the microbial community were Proteobacteria, Actinobacteriota, and Bacteroidota, while Cyanobacteria were present only with an average of 5%, with the highest concentration in the submerged intermediate layer (12%). The role of microorganisms in carbonate mineral formation was clearly demonstrated as most of the isolates were able to precipitate calcium carbonate and five of them were characterized at molecular level. Interestingly, when microbial isolates were cultivated only in filtered water, the precipitation of hazenite was observed (up to 85%), opening new prospective in P (phosphate) recovery from P depleted environments.

Comparative Genomics Unveils Functional Diversity, Pangenome Openness, and Underlying Biological Drivers among Bacillus subtilis Group

The Bacillus subtilis group (Bs group), with Bacillus subtilis as its core species, holds significant research and economic value in various fields, including science, industrial production, food, and pharmaceuticals. However, most studies have been confined to comparative genomics analyses and exploration within individual genomes at the level of species, with few conducted within groups across different species. This study focused on Bacillus subtilis, the model of Gram-positive bacteria, and 14 other species with significant research value, employing comparative pangenomics as well as population enrichment analysis to ascertain the functional enrichment and diversity. Through the quantification of pangenome openness, this work revealed the underlying biological drivers and significant correlation between pangenome openness and various factors, including the distribution of toxin-antitoxin- and integrase-related genes, as well as the number of endonucleases, recombinases, repair system-related genes, prophages, integrases, and transfer mobile elements. Furthermore, the functional enrichment results indicated the potential for secondary metabolite, probiotic, and antibiotic exploration in Bacillus licheniformis, Bacillus paralicheniformis, and Bacillus spizizenii, respectively. In general, this work systematically exposed the quantification of pangenome openness, biological drivers, the pivotal role of genomic instability factors, and mobile elements, providing targeted exploration guidance for the Bs group.

Phylogenomic and molecular markers based studies on clarifying the evolutionary relationships among Peptoniphilus species. Identification of several Genus-Level clades of Peptoniphilus species and transfer of some Peptoniphilus species to the genus Aedoeadaptatus

To clarify the evolutionary relationships among Peptoniphilus species, whose members show association with increased risk for prostate cancer, detailed phylogenomic and comparative analyses were conducted on their genome sequences. In phylogenetic trees based on core genome proteins and 16S rRNA gene sequences, Peptoniphilus species formed eight distinct clades, with Aedoeadaptatus and Anaerosphaera species branching between them. The observed clades designated as Peptoniphilus sensu stricto (encompassing its type species), Harei, Lacrimalis, Duerdenii, Mikwangii, Stercorisuis, Catoniae and Aedoeadaptatus, show genus level divergence based on 16S rRNA similarity and average amino acid identity (AAI). The Genome Taxonomy Database also assigns most of these clades to distinct taxa. Several Peptoniphilus species (viz. P. coxii, P. ivorii, P. nemausensis and some non-validly published species) grouped reliably with the type species of Aedoeadaptatus (A. acetigenes) and are affiliated to this genus based on 16S rRNA similarity, AAI, and multiple uniquely shared molecular signatures. Hence, we are proposing the transfer of these species into the emended genus Aedoeadaptatus. Our analyses on protein sequences from Peptoniphilus genomes have also identified 54 novel molecular markers consisting of conserved signature indels (CSIs), which are specific for different Peptoniphilus species clades and provide reliable means for their demarcation in molecular terms. Lastly, we also show that based on the shared presence of these CSIs in the genomes of uncharacterized Peptoniphilus spp. (cultured and uncultured), their affiliations to the specific Peptoniphilus clades can be accurately predicted. These results should prove useful in understanding the potential involvement of Peptoniphilus-related species in diseases.

Reclassification of Aestuariicella albida as Pseudomaricurvus albidus comb. nov. and Aestuariicella hydrocarbonica as Pseudomaricurvus hydrocarbonicus comb. nov. Based on Comparative Genomics and Molecular Synapomorphies

The genus Aestuariicella has been recently reclassified as a member of the family Cellvibrionaceae. However, the taxonomic position of the genus as a distinct member of the family has not been clarified. In the present study, we performed multilayered analyses anchored on genome sequences to clarify the relationship between the genera Aestuariicella and Pseudomaricurvus within the family Cellvibrionaceae. Phylogenetic analyses based on 16S rRNA gene, RNA polymerase beta subunit (RpoB) protein, and core gene sequences showed a well-supported tight cluster formed by the members of the two genera. Moreover, the analysis of the average amino acid identity (AAI) revealed that the members of the two genera shared 68.16-79.48% AAI, values which were within the range of observed AAI (≥ 67.23%) among the members of the same genus within the family Cellvibrionaceae. Members of the two genera also shared several common characteristics. Furthermore, molecular synapomorphies in a form of conserved signature indels were identified in six protein sequences that were exclusively shared by the members of the two genera. Based on the phylogenetic and molecular evidence presented here, we propose the reclassification of the species Aestuariicella albida and Aestuariicella hydrocarbonica as Pseudomaricurvus albidus comb. nov. and Pseudomaricurvus hydrocarbonicus comb. nov., respectively.

Diversity and functional assessment of indigenous culturable bacteria inhabiting fine-flavor cacao rhizosphere: Uncovering antagonistic potential against Moniliophthora roreri

The Peruvian Amazonian native cacao faces ongoing challenges that significantly undermine its productivity. Among them, frosty pod rot disease and cadmium accumulation result in losses that need for effective and environmentally safe strategies, such as those based on bacteria. To explore the biological resources in the cacao soil, a descriptive study was conducted to assess the diversity of culturable bacteria across three production districts in the Amazonas region: La Peca, Imaza, and Cajaruro. The study also focused on the functional properties of these bacteria, particularly those related to the major issues limiting cacao cultivation. For this purpose, 90 native bacterial isolates were obtained from the cacao rhizosphere. According to diversity analysis, the community was composed of 19 bacterial genera, with a dominance of the Bacillaceae family and variable distribution among the districts. This variability was statistically supported by the PCoA plots and is related to the pH of the soil environment. The functional assessment revealed that 56.8% of the isolates showed an antagonism index greater than 75% after 7 days of confrontation. After 15 days of confrontation with Moniliophthora roreri, 68.2% of the bacterial population demonstrated this attribute. This capability was primarily exhibited by Bacillus strains. On the other hand, only 4.5% were capable of removing cadmium, highlighting the biocontrol potential of the bacterial community. In addition, some isolates produced siderophores (13.63%), solubilized phosphate (20.45%), and solubilized zinc (4.5%). Interestingly, these traits showed an uneven distribution, which correlated with the divergence found by the beta diversity. Our results revealed a diverse bacterial community inhabiting the Amazonian cacao rhizosphere, showcasing crucial functional properties related to the biocontrol of M. roreri. The information generated serves as a significant resource for the development of further biotechnological tools that can be applied to native Amazonian cacao.

Novel spore-forming species exhibiting intrinsic resistance to third- and fourth-generation cephalosporins and description of Tigheibacillus jepli gen. nov., sp. nov

A comprehensive microbial surveillance was conducted at NASA's Mars 2020 spacecraft assembly facility (SAF), where whole-genome sequencing (WGS) of 110 bacterial strains was performed. One isolate, designated 179-BFC-A-HST, exhibited less than 80% average nucleotide identity (ANI) to known species, suggesting a novel organism. This strain demonstrated high-level resistance [minimum inhibitory concentration (MIC) >256 mg/L] to third-generation cephalosporins, including ceftazidime, cefpodoxime, combination ceftazidime/avibactam, and the fourth-generation cephalosporin cefepime. The results of a comparative genomic analysis revealed that 179-BFC-A-HST is most closely related to Virgibacillus halophilus 5B73CT, sharing an ANI of 78.7% and a digital DNA-DNA hybridization (dDDH) value of 23.5%, while their 16S rRNA gene sequences shared 97.7% nucleotide identity. Based on these results and the recent recognition that the genus Virgibacillus is polyphyletic, strain 179-BFC-A-HST is proposed as a novel species of a novel genus, Tigheibacillus jepli gen. nov., sp. nov (type strain 179-BFC-A-HST = DSM 115946T = NRRL B-65666T), and its closest neighbor, V. halophilus, is proposed to be reassigned to this genus as Tigheibacillus halophilus comb. nov. (type strain 5B73CT = DSM 21623T = JCM 21758T = KCTC 13935T). It was also necessary to reclassify its second closest neighbor Virgibacillus soli, as a member of a novel genus Paracerasibacillus, reflecting its phylogenetic position relative to the genus Cerasibacillus, for which we propose Paracerasibacillus soli comb. nov. (type strain CC-YMP-6T = DSM 22952T = CCM 7714T). Within Amphibacillaceae (n = 64), P. soli exhibited 11 antibiotic resistance genes (ARG), while T. jepli encoded for 3, lacking any known β-lactamases, suggesting resistance from variant penicillin-binding proteins, disrupting cephalosporin efficacy. P. soli was highly resistant to azithromycin (MIC >64 mg/L) yet susceptible to cephalosporins and penicillins.

IMPORTANCE

The significance of this research extends to understanding microbial survival and adaptation in oligotrophic environments, such as those found in SAF. Whole-genome sequencing of several strains isolated from Mars 2020 mission assembly cleanroom facilities, including the discovery of the novel species Tigheibacillus jepli, highlights the resilience and antimicrobial resistance (AMR) in clinically relevant antibiotic classes of microbes in nutrient-scarce settings. The study also redefines the taxonomic classifications within the Amphibacillaceae family, aligning genetic identities with phylogenetic data. Investigating ARG and virulence factors (VF) across these strains illuminates the microbial capability for resistance under resource-limited conditions while emphasizing the role of human-associated VF in microbial survival, informing sterilization practices and microbial management in similar oligotrophic settings beyond spacecraft assembly cleanrooms such as pharmaceutical and medical industry cleanrooms.

Characterization by MALDI-TOF MS and 16S rRNA Gene Sequencing of Aerobic Endospore-Forming Bacteria Isolated from Pharmaceutical Facility in Rio de Janeiro, Brazil

Bacillus and related genera are among the most important contaminants in the pharmaceutical production environment, and the identification of these microorganisms at the species level assists in the investigation of sources of contamination and in preventive and corrective decision making. The aim of this study was to evaluate three methodologies for the characterization of endospore-forming aerobic bacterial strains isolated from a pharmaceutical unit in Rio de Janeiro, Brazil. MALDI-TOF MS was performed using MALDI Biotyper® and VITEK® MS RUO systems, and complete 16S rRNA gene sequencing was performed using the Sanger methodology. The results showed the prevalence of the genera Bacillus (n = 9; 36.0%), Priestia (n = 5; 20.0%), and Paenibacillus (n = 4; 16.0%). Three (20.0%) strains showed <98.7% of DNA sequencing similarity on the EzBioCloud Database, indicating possible new species. In addition, the reclassification of Bacillus pseudoflexus to the genus Priestia as Priestia pseudoflexus sp. nov. is proposed. In conclusion, 16S rRNA and MALDI TOF/MS were not sufficient to identify all strains at the species level, and complementary analyses were necessary.

The host sex contributes to the endophytic bacterial community in Sargassum thunbergii and their receptacles

Endophytic bacteria have a complex coevolutionary relationship with their host macroalgae. Dioecious macroalgae are important producers in marine ecosystems, but there is still a lack of research on how sex influences their endophytic bacteria. In this study, the endophytic bacterial communities in male and female S. thunbergii and their reproductive tissues (receptacles) were compared using culture methods and high-throughput sequencing. The endophytic bacterial communities detected by the two methods were different. Among the 78 isolated strains, the dominant phylum, genus, and species were Bacillota, Alkalihalobacillus, and Alkalihalobacillus algicola, respectively, in the algal bodies, while in the receptacles, they were Bacillota, Vibrio, and Vibrio alginolyticus. However, 24 phyla and 349 genera of endophytic bacteria were identified by high-throughput sequencing, and the dominant phylum and genus were Pseudomonadota and Sva0996_ Marine_ Group, respectively, in both the algal body and the receptacles. The two methods showed similar compositions of endophytic bacterial communities between the samples of different sexes, but the relative abundances of dominant and specific taxa were different. The high-throughput sequencing results showed more clearly that the sex of the host alga had an effect on its endophyte community assembly and a greater effect on the endophytic bacterial community in the receptacles. Moreover, most specific bacteria and predicted functional genes that differed between the samples from the males and females were related to metabolism, suggesting that metabolic differences are the main causes of sex differences in the endophytic bacterial community. Our research is the first to show that host sex contributes to the composition of endophytic bacterial communities in dioecious marine macroalgae. The results enrich the database of endophytic bacteria of dioecious marine macroalgae and pave the way for better understanding the assembly mechanism of the endophytic bacterial community of algae.

Draft genome sequence of Metabacillus indicus strain EGFCL74 isolated from spontaneously fermented apple cider

Here, we report the draft genome and annotations for Metabacillus indicus strain EGFCL74, a bacterium isolated from spontaneously fermented apples. This 4.10-Mb genome adds to the limited existing data on a potential spoilage organism in natural cider ferments.

Robust demarcation of the family Peptostreptococcaceae and its main genera based on phylogenomic studies and taxon-specific molecular markers

The family Peptostreptococcaceae, which contains 15 genera including Clostridioides, presently lacks proper circumscription. Using 52 available genomes for Peptostreptococcaceae species, we report comprehensive phylogenomic and comparative analyses to reliably discern their evolutionary relationships. In phylogenetic trees based on core genome proteins and 16S rRNA gene sequences, the examined species formed a strongly supported clade designated as Peptostreptococcaceae sensu stricto. This clade encompassed the genera Peptostreptococcus (type genus), Asaccharospora, Clostridioides, Intestinibacter, Paeniclostridium, Paraclostridium, Peptacetobacter, Romboutsia and Terrisporobacter, and two misclassified species (viz. Eubacterium tenue and 'Clostridium dakarense'). The distinctness of this clade is strongly supported by eight identified conserved signature indels (CSIs), which are specific for the species from this clade. Based on the robust evidence provided by presented studies, we are proposing the emendment of family Peptostreptococcaceae to only the genera within the Peptostreptococcaceae sensu stricto clade. We also report 67 other novel CSIs, which reliably demarcate different Peptostreptococcaceae species clades and clarify the classification of some misclassified species. Based on the consistent evidence obtained from different presented studies, we are making the following proposals to clarify the classification of Peptostreptococcaceae species: (i) transfer of Eubacterium tenue, Paeniclostridium ghonii and Paeniclostridium sordellii as comb. nov. into the genus Paraclostridium; (ii) transfer of Clostridioides mangenotii as a comb. nov. into Metaclostridioides gen. nov.; (iii) classification of 'Clostridium dakarense' as a novel species Faecalimicrobium dakarense gen. nov., sp. nov. (type strain FF1T; genome and 16S rRNA accession numbers GCA_000499525.1 and KC517358, respectively); (iv) transfer of two misclassified species, Clostridium paradoxum and Clostridium thermoalcaliphilum, into Alkalithermobacter gen. nov.; and (v) proposals for two novel families, Peptoclostridiaceae fam. nov. and Tepidibacteraceae fam. nov., to accommodate remaining unclassified Peptostreptococcaceae genera. The described CSIs specific for different families and genera provide novel and reliable means for the identification, diagnostics and biochemical studies on these bacteria.

Microclimate, airborne particles, and microbiological monitoring protocol for conservation of rock-art caves: The case of the world-heritage site La Garma cave (Spain)

Cave heritage is often threatened by tourism or even scientific activities, which can lead to irreversible deterioration. We present a preventive conservation monitoring protocol to protect caves with rock art, focusing on La Garma Cave (Spain), a World Heritage Site with valuable archaeological materials and Palaeolithic paintings. This study assessed the suitability of the cave for tourist use through continuous microclimate and airborne particles monitoring, biofilm analysis, aerobiological monitoring and experimental visits. Our findings indicate several factors that make it inadvisable to adapt the cave for tourist use. Human presence and transit within the cave cause cumulative effects on the temperature of environmentally very stable and fragile sectors and significant resuspension of particles from the cave sediments. These environmental perturbations represent severe impacts as they affect the natural aerodynamic control of airborne particles and determine bacterial dispersal throughout the cave. This monitoring protocol provides part of the evidence to design strategies for sustainable cave management.

Phylogenomics studies and molecular markers reliably demarcate genus Pseudomonas sensu stricto and twelve other Pseudomonadaceae species clades representing novel and emended genera

Genus Pseudomonas is a large assemblage of diverse microorganisms, not sharing a common evolutionary history. To clarify their evolutionary relationships and classification, we have conducted comprehensive phylogenomic and comparative analyses on 388 Pseudomonadaceae genomes. In phylogenomic trees, Pseudomonas species formed 12 main clusters, apart from the "Aeruginosa clade" containing its type species, P. aeruginosa. In parallel, our detailed analyses on protein sequences from Pseudomonadaceae genomes have identified 98 novel conserved signature indels (CSIs), which are uniquely shared by the species from different observed clades/groups. Six CSIs, which are exclusively shared by species from the "Aeruginosa clade," provide reliable demarcation of this clade corresponding to the genus Pseudomonas sensu stricto in molecular terms. The remaining 92 identified CSIs are specific for nine other Pseudomonas species clades and the genera Azomonas and Azotobacter which branch in between them. The identified CSIs provide strong independent evidence of the genetic cohesiveness of these species clades and offer reliable means for their demarcation/circumscription. Based on the robust phylogenetic and molecular evidence presented here supporting the distinctness of the observed Pseudomonas species clades, we are proposing the transfer of species from the following clades into the indicated novel genera: Alcaligenes clade - Aquipseudomonas gen. nov.; Fluvialis clade - Caenipseudomonas gen. nov.; Linyingensis clade - Geopseudomonas gen. nov.; Oleovorans clade - Ectopseudomonas gen. nov.; Resinovorans clade - Metapseudomonas gen. nov.; Straminea clade - Phytopseudomonas gen. nov.; and Thermotolerans clade - Zestomonas gen. nov. In addition, descriptions of the genera Azomonas, Azotobacter, Chryseomonas, Serpens, and Stutzerimonas are emended to include information for the CSIs specific for them. The results presented here should aid in the development of a more reliable classification scheme for Pseudomonas species.

Substandard and falsified ivermectin tablets obtained for self-medication during the COVID-19 pandemic as a source of potential harm

In 2019, a global viral pandemic, due to the SARS-CoV-2 virus, broke out. Soon after, the search for a vaccine and/or antiviral medicine began. One of the candidate antiviral medicines tested was ivermectin. Although several health authorities warned the public against the use of this medicine outside clinical trials, the drug was widely used at the end of 2020 and in 2021. Simultaneously, several reports started to emerge demonstrating serious adverse effects after self-medicating with ivermectin. It stands to reason that the self-administration of substandard or falsified (SF) medicines bearing harmful quality deficiencies have contributed to this phenomenon. In order to have a better view on the nature of these harmful quality deficiencies, SF ivermectin samples, intercepted in large quantities by the Belgian regulatory agencies during the period 2021-2022, were analyzed in our official medicines control laboratory. None of the samples (n = 19) were compliant to the quality criteria applicable to medicinal products. These SF products either suffered from a systematic underdosing of the active pharmaceutical ingredient or were severely contaminated with bacteria, two of which were contaminated with known pathogens that cause gastrointestinal illness upon oral intake. In addition to the direct risks of self-medicating with such a product, the improper usage and dosage of ivermectin medication might also facilitate ivermectin tolerance or resistance in parasites. This may have detrimental consequences on a global scale, certainly as the number of newly developed active pharmaceutical ingredients that can safely be used to combat parasites is rather scarce.

Valid and accepted novel bacterial taxa derived from human clinical specimens and taxonomic revisions published in 2022

Although some nomenclature changes have caused consternation among clinical microbiologists, the discovery of novel taxa and improving classification of existing groups of organisms is exciting and adds to our understanding of microbial pathogenesis. In this mini-review, we present an in-depth summary of novel taxonomic designations and revisions to prokaryotic taxonomy that were published in 2022. Henceforth, these bacteriology taxonomic summaries will appear annually. Several of the novel Gram-positive organisms have been associated with disease, namely, the Corynebacterium kroppenstedtii-like organisms Corynebacterium parakroppenstedtii sp. nov. and Corynebacterium pseudokroppenstedtii sp. nov. A newly described Streptococcus species, Streptococcus toyakuensis sp. nov., is noteworthy for exhibiting multi-drug resistance. Among the novel Gram-negative pathogens, Vibrio paracholerae sp. nov. stands out as an organism associated with diarrhea and sepsis and has probably been co-circulating with pandemic Vibrio cholerae for decades. Many new anaerobic organisms have been described in this past year largely from genetic assessments of gastrointestinal microbiome collections. With respect to revised taxa, as discussed in previous reviews, the genus Bacillus continues to undergo further division into additional genera and reassignment of existing species into them. Reassignment of two subspecies of Fusobacterium nucleatum to species designations (Fusobacterium animalis sp. nov. and Fusobacterium vincentii sp. nov.) is also noteworthy. As was typical of previous reviews, literature updates for selected clinically relevant organisms discovered between 2017 and 2021 have been included.

Two novel alkalitolerant species Pseudalkalibacillus spartinae sp. nov. and Pseudalkalibacillus sedimenti sp. nov

In this study, two novel alkalitolerant strains (FJAT-53046T and FJAT-53715T) were isolated from sediment samples collected in Zhangzhou, PR China. Phylogeny based on 16S rRNA gene sequences suggested that strains FJAT-53046T and FJAT-53715T were new members of the genus Pseudalkalibacillus. The two novel strains showed the highest 16S rRNA gene sequence similarity to Pseudalkalibacillus hwajinpoensis DSM 16206T, with values of 97.4 and 97.6 %, respectively. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains and the reference strain were 77.2 and 79.6 %, 20.9 and 30.2 %, respectively, which were below the prokaryotic species delineation thresholds. The ANI and dDDH values between strains FJAT-53046T and FJAT-53715T were 86.0 and 30.2 %, respectively, suggesting that they belonged to different species in the genus Pseudalkalibacillus. The major respiratory quinone in both strains was MK-7 and the major cellular fatty acids were anteiso-C15 : 0 and anteiso-C17 : 0. Diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine were the major polar lipids in both novel strains. Combined with results stemming from the determination of physical and biochemical characteristics, chemical properties, and genome analysis, strains FJAT-53046T and FJAT-53715T are proposed to represent two novel species of the genus Pseudalkalibacillus, for which the names Pseudalkalibacillus spartinae sp. nov. and Pseudalkalibacillus sedimenti sp. nov. are proposed. The type strains are FJAT-53046T (=GDMCC 1.3077T=JCM 35611T) and FJAT-53715T (=GDMCC 1.3076T=JCM 35610T), respectively.

Uncovering the Secrets of Slow-Growing Bacteria in Tropical Savanna Soil Through Isolation and Genomic Analysis

One gram of soil holds ten billion bacteria of thousands of different species, but most remain unknown, and one of the serious issues is intrinsic to slow-growing bacteria. In this study, we aimed to isolate and characterize slow-growing bacteria from Brazilian Cerrado soil. Over a period of 4 weeks, we conducted an incubation process and selected a total of 92 isolates. These isolates, consisting mostly of slow-growing bacteria, have the ability to thrive in low-water conditions and possess features that promote plant growth. To identify the isolated bacteria, we performed 16S rRNA sequencing analysis and found that the slow-growing strains were genetically similar to known bacterial species but also belonged to a novel group of species. The new strains identified were Caballeronia sp., Neobacillus sp., Bradyrhizobium sp., and high GC Gram-positive species. Furthermore, we conducted growth experiments using various culture media and temperature conditions. These experiments revealed an extended lag phase for five strains, indicating their slow growth characteristics. Genomic analysis of these five slow-growing bacteria showed their potential to participate in biogeochemical cycles, metabolize various carbohydrates, encode proteins with a role in promoting plant growth and have biosynthetic potential for secondary metabolites. Taken together, our findings reveal the untapped potential of slow-growing bacteria in tropical savanna soils.

Simply Versatile: The Use of Peribacillus simplex in Sustainable Agriculture

Peribacillus simplex is a Gram-positive, spore-forming bacterium derived from a vast range of different origins. Notably, it is part of the plant-growth-promoting rhizobacterial community of many crops. Although members of the Bacillaceae family have been widely used in agriculture, P. simplex has, so far, remained in the shadow of its more famous relatives, e.g., Bacillus subtilis or Bacillus thuringiensis. Recent studies have, however, started to uncover the bacterium's highly promising and versatile properties, in particular in agricultural and environmental applications. Hence, here, we review the plant-growth-promoting features of P. simplex, as well as its biocontrol activity against a variety of detrimental plant pests in different crops. We further highlight the bacterium's potential as a bioremediation agent for environmental contaminants, such as metals, pesticide residues, or (crude) oil. Finally, we examine the recent developments in the European regulatory landscape to facilitate the use of microorganisms in plant protection products. Undoubtedly, further studies on P. simplex will reveal additional benefits for agricultural and environmentally friendly applications.

Update on the genus Robertmurraya: a bacterial genus honoring Dr. Robert G.E. Murray (with some personal reminiscences)

The genus Robertmurraya was created by my group in 2020 to recognize the contributions of Dr. Robert G.E. Murray to the field of prokaryotic taxonomy. This manuscript updates the information regarding this genus. In addition to the seven Robertmurraya species with validly published names, the work presented here shows that two species with effectively published names, "Bacillus yapensis" and "Bacillus dakarensis", and an uncharacterized Bacillus sp. Y1 are also affiliated with this genus. Based on these results, reclassification of "Bacillus yapensis" as a novel species Robertmurraya yapensis sp. nov. is proposed. It is also suggested that "Bacillus dakarensis", for which strains are not available from culture collections, should also be recognized as "Robertmurraya dakarensis". This article also reflects on the serendipitous way I came to know Dr. Murray and his extensive interactions with me and strong support for our work for more than 10 years. Dr. Murray also introduced me and our work to his friend and contemporary Dr. Peter Sneath, who like him also contributed extensively to the field of prokaryotic taxonomy. This introduction led to a fruitful collaboration with Dr. Sneath leading to a joint publication describing the use of the Character Compatibility approach to molecular sequence data.

Phylogenomic and molecular markers based studies on Staphylococcaceae and Gemella species. Proposals for an emended family Staphylococcaceae and three new families (Abyssicoccaceae fam. nov., Salinicoccaceae fam. nov. and Gemellaceae fam. nov.) harboring four new genera, Lacicoccus gen. nov., Macrococcoides gen. nov., Gemelliphila gen. nov., and Phocicoccus gen. nov

The family Staphylococcacae and genus Gemella contain several organisms of clinical or biotechnological importance. We report here comprehensive phylogenomic and comparative analyses on 112 available genomes from species in these taxa to clarify their evolutionary relationships and classification. In a phylogenomic tree based on 678 core proteins, Gemella species were separated from Staphylococcacae by a long branch indicating that they constitute a distinct family (Gemellaceae fam. nov.). In this tree, Staphylococcacae species formed two main clades, one encompassing the genera Aliicoccus, Jeotgalicoccus, Nosocomiicoccus and Salinicoccus (Family "Salinicoccaceae"), while the other clade consisted of the genera Macrococcus, Mammaliicoccus and Staphylococcus (Family Staphylococcaceae emend.). In this tree, species from the genera Gemella, Jeotgalicoccus, Macrococcus and Salinicoccus each formed two distinct clades. Two species clades for these genera are also observed in 16S rRNA gene trees and supported by average amino acid identity analysis. We also report here detailed analyses on protein sequences from Staphylococcaceae and Gemella genomes to identify conserved signature indels (CSIs) which are specific for different genus and family-level clades. These analyses have identified 120 novel CSIs robustly demarcating different proposed families and genera. The identified CSIs provide independent evidence that the genera Gemella, Jeotgalicoccus, Macrococcus and Salinicoccus consist of two distinct clades, which can be reliably distinguished based on multiple exclusively shared CSIs. We are proposing transfers of the species from the novel clades of the above four genera into the genera Gemelliphila gen. nov., Phocicoccus gen. nov., Macrococcoides gen. nov. and Lacicoccus gen. nov., respectively. The identified CSIs also provide strong evidence for division of Staphylococcaceae into an emended family Staphylococcaceae and two new families, Abyssicoccaceae fam. nov. and Salinicoccaceae fam. nov. All of these families can be reliably demarcated based on several exclusively shared CSIs.

Proposal to transfer Bacillus massiliigorillae to the genus Peribacillus as Peribacillus massiliigorillae comb. nov., and Bacillus sinesaloumensis to the genus Ferdinandcohnia as Ferdinandcohnia sinesaloumensis comb. nov

The present study was carried out to clarify the taxonomic position of Bacillus massiliigorillae and Bacillus sinesaloumensis. The 16S rRNA gene sequences extracted from the Bacillus sinesaloumensis Marseille-P3516T (FTOX00000000) and Bacillus massiliigorillae G2T (CAVL000000000) genomes showed 98.5 and 99.1% similarity with the type strains of Ferdinandcohnia humi and Peribacillus endoradicis, respectively. The amino acid identity (AAI) values of Bacillus sinesaloumensis Marseille-P3516T were higher with Ferdinandcohnia members, while Bacillus massiliigorillae G2T with Peribacillus members. In phylogenomic and phylogenetic trees, Bacillus sinesaloumensis Marseille-P3516T and Bacillus massiliigorillae G2T clade with members of the genera Ferdinandcohnia and Peribacillus, respectively. Based on the above results, we propose to transfer Bacillus massiliigorillae to the genus Peribacillus as Peribacillus massiliigorillae comb. nov., and Bacillus sinesaloumensis to the genus Ferdinandcohnia as Ferdinandcohnia sinesaloumensis comb. nov.

Implications of Sample Preparation Methods on the MALDI-TOF MS Identification of Spore-Forming Bacillus Species from Food Samples: A Closer Look at Bacillus licheniformis, Peribacillus simplex, Lysinibacillus fusiformis, Bacillus flexus, and Bacillus marisflavi

This research underscores the criticality of tailored culture conditions and incubation periods for effective and accurate identification of spore-forming bacteria: Bacillus licheniformis, Peribacillus simplex, Lysinibacillus fusiformis, Bacillus flexus, and Bacillus marisflav, isolated from food samples, utilizing the MALDI-TOF MS technique. All isolated strains were confirmed as Gram-positive bacteria from diverse genera through 16S rDNA gene sequencing. To enhance the accuracy of the identification process, the study employed an optimization strategy involving a varied incubation time (ranging from 1 to 48 h) and two distinct sample preparation approaches-direct transfer facilitated by formic acid and protein extraction via ethanol. It was observed that matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) could successfully identify approximately 47% of the samples following a 24 h incubation period. The study emphasizes the critical role of sample preparation methods in enabling precise bacterial identification. Our findings reveal the necessity of tailoring the incubation time for each sample, as the optimum period for accurate identification fluctuated between 1 and 12 h. Further demonstrating the interplay between incubation time and spore quantity, our study used the Schaeffer-Fulton staining method to show that the lowest spore counts were detected between 5 and 8 h of incubation. This provides evidence that spore formation impacts bacterial identification. Our research thus deepens the understanding of spore-forming bacteria identification using MALDI-TOF MS and illuminates the various factors affecting the dependability and accuracy of this technique. Future research may explore additional variables, such as the effect of varying culture media, to further augment identification accuracy and gain a holistic understanding of spore-forming bacterial behavior in food samples. By enhancing our knowledge, these findings can substantially contribute to improving food safety and quality assurance strategies by enabling the more accurate and efficient identification of spore-forming bacteria in the food industry, thereby elevating the standards of food safety.

The master regulator for entry into sporulation in Bacillus subtilis becomes a mother cell-specific transcription factor for forespore engulfment

The Spo0A transcription factor is activated by phosphorylation in starving Bacillus subtilis cells. The activated Spo0A (Spo0A~P) regulates genes controlling entry into sporulation and appears to control mother-cell-specific gene expression after asymmetric division, but the latter remains elusive. Here, we found that Spo0A~P directly binds to three conserved DNA sequences (0A1-3) in the promoter region of the mother cell-specific lytic transglycosylase gene spoIID, which is transcribed by σE -RNA polymerase (RNAP) and negatively controlled by the SpoIIID transcription factor and required for forespore engulfment. Systematic mutagenesis of the 0A boxes revealed that the 0A1 and 0A2 boxes located upstream of the promoter positively control the transcription of spoIID. In contrast, the 0A3 box located downstream of the promoter negatively controls the transcription of spoIID. The mutated SpoIIID binding site located between the -35 and -10 promoter elements causes increased expression of spoIID and reduced sporulation. When the mutations of 0A1, 0A2, and IIID sites are combined, sporulation is restored. Collectively, our data suggest that the mother cell-specific spoIID expression is precisely controlled by the coordination of three factors, Spo0A~P, SpoIIID, and σE -RNAP, for proper sporulation. The conservation of this mechanism across spore-forming species was discussed.

Biocontrol of bacterial seedling rot of rice plants using combination of Cytobacillus firmus JBRS159 and silicon

Burkholderia glumae causes bacterial panicle blight (BPB) and bacterial seedling rot (BSR) which are difficult to control in rice plants. Seed disinfection using microbes and eco-friendly materials is an efficient alternative practice for managing BPB and BSR. In this study, we applied Cytobacillus firmus JBRS159 (JBRS159) in combination with silicon dioxide (SiO2) nanoparticle or potassium silicate (K2SiO3) solution to control BSR. JBRS159, SiO2 nanoparticle, and K2SiO3 independently suppressed the BSR disease and promoted growths of rice and Arabidopsis. Population of B. glumae in the treated rice seeds was suppressed by the application of JBRS159 via competitions for nutrients and niches. The mixture of JBRS159 and each Si compound (SiO2 nanoparticle or K2SiO3) was complementary for disease-suppressing and growth-promoting activities of individual treatment. The results of this study indicate that mixture of JBRS159 with each Si compound can be harnessed for disease control and growth promotion as efficient alternatives to chemical pesticides and synthetic fertilizers. The efficacy of JBRS159 and Si compounds in the control of BSR and BPB in the field remains to be evaluated.

Alkalicoccobacillus porphyridii sp. nov., isolated from a marine red alga, reclassification of Shouchella plakortidis and Shouchella gibsonii as Alkalicoccobacillus plakortidis comb. nov. and Alkalicoccobacillus gibsonii comb. nov., and emended description of the genus Alkalicoccobacillus Joshi et al. 2022

A Gram-stain-positive alkali-tolerant and strictly aerobic bacterium, designated strain P16T, was isolated from a marine red alga, Porphyridium cruentum, in the Yellow Sea, Republic of Korea. Cells were motile rods with peritrichous flagella and exhibited catalase and oxidase activities. The optimal growth of strain P16T was observed to occur at 30 °C and pH 8.0 and in the presence of 2.0 % (w/v) NaCl. Menaquinone-7 was identified as the sole respiratory quinone. Strain P16T contained anteiso-C15 : 0, iso-C15 : 0, iso-C14 : 0 and iso-C16 : 0, and diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine as major cellular fatty acids and polar lipids, respectively. The G+C content of strain P16T was 40.8 mol%. Strain P16T was most closely related to Shouchella plakortidis P203T, Shouchella gibsonii DSM 8722T and Alkalicoccobacillus murimartini LMG 21005T with 98.1, 98.1 and 98.0 % 16S rRNA gene sequence similarities, respectively. Phylogenetic analyses based on 16S rRNA gene and genome sequences revealed that strain P16T, S, plakortidis, S. gibsonii and A. murimartini formed a single phylogenetic lineage cluster, and genomic relatedness analyses showed that they are different species. Based on phylogenetic, phenotypic, chemotaxonomic and molecular features, strain P16T represents a novel species of the genus Alkalicoccobacillus, for which the name Alkalicoccobacillus porphyridii sp. nov. is proposed. The type strain is P16T (=KACC 19520T=JCM 32931T). In addition, S. plakortidis and S. gibsonii are reclassified as Alkalicoccobacillus plakortidis comb. nov. (type strain P203T=DSM 19153T=NCIMB 14288T) and Alkalicoccobacillus gibsonii comb. nov. (type strain PN-109T=ATCC 700164T=DSM 8722T=KCCM 41407T), respectively.

Polychlorinated Biphenyl Transformation, Peroxidase and Oxidase Activities of Fungi and Bacteria Isolated from a Historically Contaminated Site

Causing major health and ecological disturbances, polychlorinated biphenyls (PCBs) are persistent organic pollutants still recovered all over the world. Microbial PCB biotransformation is a promising technique for depollution, but the involved molecular mechanisms remain misunderstood. Ligninolytic enzymes are suspected to be involved in many PCB transformations, but their assessments remain scarce. To further inventory the capabilities of microbes to transform PCBs through their ligninolytic enzymes, we investigated the role of oxidase and peroxidase among a set of microorganisms isolated from a historically PCB-contaminated site. Among 29 isolated fungi and 17 bacteria, this work reports for the first time the PCB-transforming capabilities from fungi affiliated to Didymella, Dothiora, Ilyonectria, Naganishia, Rhodoturula, Solicoccozyma, Thelebolus and Truncatella genera and bacteria affiliated to Peribacillus frigotolerans, Peribacillus muralis, Bacillus mycoides, Bacillus cereus, Bacillus toyonensis, Pseudarthrobacter sp., Pseudomonas chlororaphis, Erwinia aphidicola and Chryseobacterium defluvii. In the same way, this is the first report of fungal isolates affiliated to the Dothiora maculans specie and Cladosporium genus that displayed oxidase (putatively laccase) and peroxidase activity, respectively, enhanced in the presence of PCBs (more than 4-fold and 20-fold, respectively, compared to controls). Based on these results, the observed activities are suspected to be involved in PCB transformation.

Culturomics and Circular Agronomy: Two Sides of the Same Coin for the Design of a Tailored Biofertilizer for the Semi-Halophyte Mesembryanthemum crystallinum

According to the EU, the global consumption of biomass, fossil fuels, metals, and minerals is expected to double by 2050, while waste will increase by 70%. In this context, the Circular Economy Action Plan (CEAP) intends to integrate development and sustainability. In this regard, tailored biofertilizers based on plant growth-promoting bacteria (PGPB) can improve plant yield with fewer inputs. In our project, an autochthonous halophyte of the Andalusian marshes, namely Mesembryanthemum crystallinum, was selected for its interest as a source of pharmaceuticals and nutraceuticals. The aim of this work was to use a culturomics approach for the isolation of specific PGPB and endophytes able to promote plant growth and, eventually, modulate the metabolome of the plant. For this purpose, a specific culture medium based on M. crystallinum biomass, called Mesem Agar (MA), was elaborated. Bacteria of three compartments (rhizosphere soil, root endophytes, and shoot endophytes) were isolated on standard tryptone soy agar (TSA) and MA in order to obtain two independent collections. A higher number of bacteria were isolated on TSA than in MA (47 vs. 37). All the bacteria were identified, and although some of them were isolated in both media (Pseudomonas, Bacillus, Priestia, Rosellomorea, etc.), either medium allowed the isolation of specific members of the M. crystallinum microbiome such as Leclercia, Curtobacterium, Pantoea, Lysinibacillus, Mesobacillus, Glutamicibacter, etc. Plant growth-promoting properties and extracellular degrading activities of all the strains were determined, and distinct patterns were found in both media. The three best bacteria of each collection were selected in order to produce two different consortia, whose effects on seed germination, root colonization, plant growth and physiology, and metabolomics were analyzed. Additionally, the results of the plant metabolome revealed a differential accumulation of several primary and secondary metabolites with pharmaceutical properties. Overall, the results demonstrated the feasibility of using "low cost media" based on plant biomass to carry out a culturomics approach in order to isolate the most suitable bacteria for biofertilizers. In this way, a circular model is established in which bacteria help plants to grow, and, in turn, a medium based on plant wastes supports bacterial growth at low prices, which is the reason why this approach can be considered within the model of "circular agronomy".

Alkalihalobacillus deserti sp. nov., Isolated from the Saline-Alkaline Soil

A bacterial strain, designated TRPH29^T, was isolated from saline-alkaline soil, collected from the southern edge of the Gurbantunggut desert, Xinjiang, People's Republic of China. The isolate was Gram-staining positive, facultatively anaerobic, straight rods. Growth occurred at 15-40 °C (optimum, 28 °C), pH 8.0-13.0 (optimum, 10.0), and in the presence of 0-15% (w/v) NaCl (optimum, 2%). Phylogenetic analysis using 16S rRNA gene sequence indicated that strain TRPH29^T showed the highest sequence similarities to Alkalihalobacillus krulwichiae (98.31%), Alkalihalobacillus wakoensis (98.04%), and Alkalihalobacillus akibai (97.69%). Average nucleotide identity (ANI) and digital DNA-DNA hybridization values between strain TRPH29^T and Alkalihalobacillus krulwichiae, Alkalihalobacillus wakoensis, Alkalihalobacillus akibai were in the range of 73.62-75.52% and 15.0-21.20%, respectively. Results of genome analyses indicated that the genome size of strain TRPH29^T was 5.05 Mb, with a genomic DNA G + C content of 37.30%. Analysis of the cellular component of strain TRPH29^T revealed that the primary fatty acids were anteiso-C_15:0 and iso-C_15:0, and the polar lipids included diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unidentified glycolipid, and an unidentified phospholipid. The predominant respiratory quinone was MK-7. Based on the genomic, phylogenetic, phenotypic and chemotaxonomic analyses, strain TRPH29^T represents a novel species of the genus Alkalihalobacillus, for which the name Alkalihalobacillus deserti sp. nov. is proposed. The type strain is TRPH29^T (= CGMCC 1.19067^T = NBRC 115475^T).

New robust subtilisins from halotolerant and halophilic Bacillaceae

The aim of the present study was the characterisation of three true subtilisins and one phylogenetically intermediate subtilisin from halotolerant and halophilic microorganisms. Considering the currently growing enzyme market for efficient and novel biocatalysts, data mining is a promising source for novel, as yet uncharacterised enzymes, especially from halophilic or halotolerant Bacillaceae, which offer great potential to meet industrial needs. Both halophilic bacteria Pontibacillus marinus DSM 16465^T and Alkalibacillus haloalkaliphilus DSM 5271^T and both halotolerant bacteria Metabacillus indicus DSM 16189 and Litchfieldia alkalitelluris DSM 16976^T served as a source for the four new subtilisins SPPM, SPAH, SPMI and SPLA. The protease genes were cloned and expressed in Bacillus subtilis DB104. Purification to apparent homogeneity was achieved by ethanol precipitation, desalting and ion-exchange chromatography. Enzyme activity could be observed between pH 5.0-12.0 with an optimum for SPPM, SPMI and SPLA around pH 9.0 and for SPAH at pH 10.0. The optimal temperature for SPMI and SPLA was 70 °C and for SPPM and SPAH 55 °C and 50 °C, respectively. All proteases showed high stability towards 5% (w/v) SDS and were active even at NaCl concentrations of 5 M. The four proteases demonstrate potential for future biotechnological applications. KEY POINTS: • Halophilic and halotolerant Bacillaceae are a valuable source of new subtilisins. • Four new subtilisins were biochemically characterised in detail. • The four proteases show potential for future biotechnological applications.

Rhizosphere Microbiota Promotes the Growth of Soybeans in a Saline-Alkali Environment under Plastic Film Mulching

The rhizosphere microbiota plays a critical and crucial role in plant health and growth, assisting plants in resisting adverse stresses, including soil salinity. Plastic film mulching is an important method to adjust soil properties and improve crop yield, especially in saline-alkali soil. However, it remains unclear whether and to what extent the association between these improvements and rhizosphere microbiota exists. Here, from a field survey and a greenhouse mesocosm experiment, we found that mulching plastic films on saline-alkali soil can promote the growth of soybeans in the field. Results of the greenhouse experiment showed that soybeans grew better in unsterilized saline-alkali soil than in sterilized saline-alkali soil under plastic film mulching. By detecting the variations in soil properties and analyzing the high-throughput sequencing data, we found that with the effect of film mulching, soil moisture content was effectively maintained, soil salinity was obviously reduced, and rhizosphere bacterial and fungal communities were significantly changed. Ulteriorly, correlation analysis methods were applied. The optimization of soil properties ameliorated the survival conditions of soil microbes and promoted the increase in relative abundance of potential beneficial microorganisms, contributing to the growth of soybeans. Furthermore, the classification of potential key rhizosphere microbial OTUs were identified. In summary, our study suggests the important influence of soil properties as drivers on the alteration of rhizosphere microbial communities and indicates the important role of rhizosphere microbiota in promoting plant performance in saline-alkali soil under plastic film mulching.

Unveiling the genomic potential of a novel thermostable glycoside hydrolases producing Neobacillus sedimentimangrovi UE25

Genetic and enzymatic potential of Neobacillus sedimentimangrovi has not been assembled to date. Here, we report a high-quality genome assembly of thermophilic bacterium Neobacillus sedimentimangrovi UE25 using Illumina Hi-seq 2500. The strain was isolated from a crocodile pond Manghopir, Karachi, Pakistan. QUAST quality parameters showed 37.75% GC content and exhibited the genome into 110 contigs, with a total size of 3,230,777 bases. Genome of N. sedimentimangrovi UE25 harbors phage mediated DNA through horizontal gene exchange from the phages, symbiotic and pathogenic bacteria. Most of the phage genome encodes for hypothetical proteins, protease, and phage assembly proteins. Gene clusters encoding the intrinsic resistance to glycopeptides, isoniazid, rifamycin, elfamycin, macrolide, aminoglycosides, tetracycline and fluoroquinolone were identified into the genome. Since, the strain has been reported for the production of many industrially important thermostable enzymes, therefore, the genomic data of thermostable enzymes might be helpful to employ this species in commercial sectors. Probing genes of multiple thermostable glycoside hydrolase enzymes especially xylanases of N. sedimentimangrovi UE25 showed genetic diversity among the genes and confer the industrial importance of this microorganism. Furthermore, the genome of N. sedimentimangrovi will greatly improve our understanding of its genetics and evolution.

Structural and functional characterization of a multi-domain GH92 α-1,2-mannosidase from Neobacillus novalis

Many secreted eukaryotic proteins are N-glycosylated with oligosaccharides composed of a high-mannose N-glycan core and, in the specific case of yeast cell-wall proteins, an extended α-1,6-mannan backbone carrying a number of α-1,2- and α-1,3-mannose substituents of varying lengths. α-Mannosidases from CAZy family GH92 release terminal mannose residues from these N-glycans, providing access for the α-endomannanases, which then degrade the α-mannan backbone. Most characterized GH92 α-mannosidases consist of a single catalytic domain, while a few have extra domains including putative carbohydrate-binding modules (CBMs). To date, neither the function nor the structure of a multi-domain GH92 α-mannosidase CBM has been characterized. Here, the biochemical investigation and crystal structure of the full-length five-domain GH92 α-1,2-mannosidase from Neobacillus novalis (NnGH92) with mannoimidazole bound in the active site and an additional mannoimidazole bound to the N-terminal CBM32 are reported. The structure of the catalytic domain is very similar to that reported for the GH92 α-mannosidase Bt3990 from Bacteroides thetaiotaomicron, with the substrate-binding site being highly conserved. The function of the CBM32s and other NnGH92 domains was investigated by their sequential deletion and suggested that whilst their binding to the catalytic domain was crucial for the overall structural integrity of the enzyme, they appear to have little impact on the binding affinity to the yeast α-mannan substrate. These new findings provide a better understanding of how to select and optimize other multi-domain bacterial GH92 α-mannosidases for the degradation of yeast α-mannan or mannose-rich glycans.

AppIndels.com server: a web-based tool for the identification of known taxon-specific conserved signature indels in genome sequences. Validation of its usefulness by predicting the taxonomic affiliation of >700 unclassified strains of Bacillus species

Taxon-specific conserved signature indels (CSIs) in genes/proteins provide reliable molecular markers (synapomorphies) for unambiguous demarcation of taxa of different ranks in molecular terms and for genetic, biochemical and diagnostic studies. Because of their predictive abilities, the shared presence of known taxon-specific CSIs in genome sequences has proven useful for taxonomic purposes. However, the lack of a convenient method for identifying the presence of known CSIs in genome sequences has limited their utility for taxonomic and other studies. We describe here a web-based tool/server (AppIndels.com) that identifies the presence of known and validated CSIs in genome sequences and uses this information for predicting taxonomic affiliation. The utility of this server was tested by using a database of 585 validated CSIs, which included 350 CSIs specific for ≈45 Bacillales genera, with the remaining CSIs being specific for members of the orders Neisseriales, Legionellales and Chlorobiales, family Borreliaceae, and some Pseudomonadaceae species/genera. Using this server, genome sequences were analysed for 721 Bacillus strains of unknown taxonomic affiliation. Results obtained showed that 651 of these genomes contained significant numbers of CSIs specific for the following Bacillales genera/families: Alkalicoccus, 'Alkalihalobacillaceae', Alteribacter, Bacillus Cereus clade, Bacillus Subtilis clade, Caldalkalibacillus, Caldibacillus, Cytobacillus, Ferdinandcohnia, Gottfriedia, Heyndrickxia, Lederbergia, Litchfieldia, Margalitia, Mesobacillus, Metabacillus, Neobacillus, Niallia, Peribacillus, Priestia, Pseudalkalibacillus, Robertmurraya, Rossellomorea, Schinkia, Siminovitchia, Sporosarcina, Sutcliffiella, Weizmannia and Caryophanaceae. Validity of the taxon assignment made by the server was examined by reconstructing phylogenomic trees. In these trees, all Bacillus strains for which taxonomic predictions were made correctly branched with the indicated taxa. The unassigned strains likely correspond to taxa for which CSIs are lacking in our database. Results presented here show that the AppIndels server provides a useful new tool for predicting taxonomic affiliation based on shared presence of the taxon-specific CSIs. Some caveats in using this server are discussed.

A molecular study on recombinant pullulanase type I from Metabacillus indicus

Despite the great potential of cold-adapted pullulanase type I in tremendous industrial applications, the majority of commercialized pullulnases type I are of mesophilic and thermophilic origin so far. Hence, the present study underlines cloning, heterologous expression in Escherichia coli, characterization, and in silico structural modeling of Metabacillus indicus open reading frame of cold-adapted pullulanase type I (Pull_Met: 2133 bp & 710 a.a) for the first time ever. The predicted Pull_Met tertiary structure by I-TASSER, was structurally similar to PDB 2E9B pullulanase of Bacillus subtilis. Purified to homogeneity Pull_Met showed specific activity (667.6 U/mg), fold purification (31.7), molecular mass (79.1 kDa), monomeric subunit and Km (2.63 mg/mL) on pullulan. Pull_Met had optimal pH (6.0) and temperature (40 ^oC). After 10 h pre-incubation at pH 2.6-6.0, Pull_Met maintained 47.12 ± 0.0-35.28 ± 1.64% of its activity. After 120 min pre-incubation at 30 ^oC, the retained activity was 51.11 ± 0.29%. At 10 mM Mn²⁺, Na²⁺, Ca²⁺, Mg²⁺, and Cu²⁺ after 30 min preincubation, retained activity was 155.89 ± 8.97, 134.71 ± 1.82, 97.64 ± 7.06, 92.25 ± 4.18, and 71.28 ± 1.10%, respectively. After 30 min pre-incubation with Tween-80, Tween-20, Triton X-100, and commercially laundry detergents at 0.1% (v/v), the retained activity was 141.15 ± 3.50, 145.45 ± 0.20, 118.12 ± 11.00, and 90%, respectively. Maltotriose was the only end product of pullulan hydrolysis. Synergistic action of CA-AM21 (α-amylase) and Pull_Met on starch liberated 16.51 g reducing sugars /g starch after 1 h at 40 ^oC. Present data (cold-adeptness, detergent stability, and ability to exhibit starch saccharification of Pull_Met) underpins it as a promising pullulanase type I for industrial exploitation.

Characterization of the Bacterial Communities Inhabiting Tropical Propolis of Puerto Rico

Propolis is a resinous material produced by honeybees from different plant sources and used in the hive as a building material and to protect the colony from parasites and pathogens. Despite its antimicrobial properties, recent studies showed that propolis hosts diverse microbial strains, some with great antimicrobial potential. In this study, the first description of the bacterial community of propolis produced by the gentle Africanized honeybee was reported. Propolis was sampled from hives of two different geographic areas of Puerto Rico (PR, USA), and the associated microbiota investigated by both cultivation and metataxonomic approaches. Metabarcoding analysis showed appreciable bacterial diversity in both areas and statistically significant dissimilarity in the taxa composition of the two areas, probably due to the different climatic conditions. Both metabarcoding and cultivation data revealed the presence of taxa already detected in other hive components and compatible with the bee's foraging environment. Isolated bacteria and propolis extracts showed antimicrobial activity against Gram-positive and Gram-negative bacterial tester strains. These results support the hypothesis that the propolis microbiota could contribute to propolis' antimicrobial properties.

Phylogenomics and molecular marker-based analyses of the order Nevskiales: Proposal for the creation of Steroidobacterales ord. nov. and Peristeroidobacter gen. nov

The order Nevskiales, class Gammaproteobacteria, encompasses four families Algiphilaceae, Salinisphaeraceae, Nevskiaceae, and Steroidobacteraceae. The taxonomy of this order is structured from the inferences derived from the 16S rRNA gene and genome-based phylogenetic tree analyses. However, previous taxonomic studies of the order failed to incorporate most of the representatives from other established orders within the class Gammaproteobacteria. Other divergent members within the class Gammaproteobacteria were therefore overlooked. In this study, the taxonomy of the order Nevskiales was revisited using genome-based analyses with an expanded scope of outgroups representing the vast majority of the diversity within the class Gammaproteobacteria. Results from the phylogenetic analyses strongly supported the exclusion of the family Steroidobacteraceae from the order Nevskiales and further implied the assignment of the family into a novel order. In addition, the analyses also supported the reclassification of Steroidobacter gossypii, Steroidobacter soli, Steroidobacter agariperforans, and Steroidobacter agaridevorans into a novel genus. The identified conserved signature indels in 33 protein sequences further reinforced the new taxonomic assignments. Furthermore, the results of the average nucleotide identity and average amino acid identity analyses, together with the phenotypic and genomic characteristics among the members of the genus Steroidobacter also provided evidence supporting the reclassification of the four Steroidobacter species. Based on these results, the family Steroidobacteraceae is proposed to be assigned into a novel order Steroidobacterales ord. nov., and the species S. gossypii, S. soli, S. agariperforans, and S. agaridevorans are proposed to be moved into a novel genus Peristeroidobacter gen. nov. within the family Steroidobacteraceae.

A model industrial workhorse: Bacillus subtilis strain 168 and its genome after a quarter of a century

The vast majority of genomic sequences are automatically annotated using various software programs. The accuracy of these annotations depends heavily on the very few manual annotation efforts that combine verified experimental data with genomic sequences from model organisms. Here, we summarize the updated functional annotation of Bacillus subtilis strain 168, a quarter century after its genome sequence was first made public. Since the last such effort 5 years ago, 1168 genetic functions have been updated, allowing the construction of a new metabolic model of this organism of environmental and industrial interest. The emphasis in this review is on new metabolic insights, the role of metals in metabolism and macromolecule biosynthesis, functions involved in biofilm formation, features controlling cell growth, and finally, protein agents that allow class discrimination, thus allowing maintenance management, and accuracy of all cell processes. New 'genomic objects' and an extensive updated literature review have been included for the sequence, now available at the International Nucleotide Sequence Database Collaboration (INSDC: AccNum AL009126.4).

Revisiting the taxonomy of the genus Rhodopirellula with the proposal for reclassification of the genus to Rhodopirellula sensu stricto, Aporhodopirellula gen. nov., Allorhodopirellula gen. nov. and Neorhodopirellula gen. nov

The current genus Rhodopirellula consists of marine bacteria which belong to the family Pirellulaceae of the phylum Planctomycetota. Members of the genus Rhodopirellula are aerobic, mesophiles and chemoheterotrophs. The here conducted analysis built on 16S rRNA gene sequence and multi-locus sequence analysis based phylogenomic trees suggested that the genus is subdivided into four clades. Existing Rhodopirellula species were studied extensively based on phenotypic, genomic and chemotaxonomic parameters. The heterogeneity was further confirmed by overall genome-related indices (OGRI) including digital DNA-DNA hybridization (dDDH), average nucleotide identity (ANI), average amino acid identity (AAI), and percentage of conserved proteins (POCP). AAI and POCP values between the clades of the genus Rhodopirellula were 62.2-69.6% and 49.5-62.5%, respectively. Comparative genomic approaches like pan-genome analysis and conserved signature indels (CSIs) also support the division of the clades. The genomic incoherence of the members of the genus is further supported by variations in phenotypic characteristics. Thus, with the here applied integrated comparative genomic and polyphasic approaches, we propose the reclassification of the genus Rhodopirellula to three new genera: Aporhodopirellula gen. nov., Allorhodopirellula gen. nov., and Neorhodopirellula gen. nov.

Cytobacillus citreus sp. nov., isolated from citrus rhizosphere soil

A Gram-stain-positive, rod-shaped and motile strain, designated FJAT-49705^T, was isolated from the citrus rhizosphere soil sample. Strain FJAT-49705^T grew at 20-40 °C (optimum, 30 °C) and pH 6.0-11.0 (optimum, pH 7.0) with 0-5 % (w/v) NaCl (optimum, 2 %). Strain FJAT-49705^T showed high 16S rRNA gene sequence similarity to 'Bacillus dafuensis' FJAT-25496^T (99.7 %) and Cytobacillus solani FJAT-18043^T (98.0 %). In phylogenetic (based on 16S rRNA gene sequences) and phylogenomic trees (based on 71 bacterial single-copy genes), strain FJAT-49705^T clustered with the members of the genus Cytobacillus. MK-7 was the only isoprenoid quinone present. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and an unidentified phospholipid. The major fatty acids were anteiso-C_15 : 0 and iso-C_15 : 0. The genomic DNA G+C content was 36.9 %. The average nucleotide identity (ANI) values between FJAT-49705^T and 'B. dafuensis' FJAT-25496^T and C. solani FJAT-18043^T were below the cut-off level (95-96 %) recommended as the ANI criterion for interspecies identity. Based on the above results, strain FJAT-49705^T represents a novel species of the genus Cytobacillus, for which the name Cytobacillus citreus sp. nov. is proposed. The type strain is FJAT-49705^T (=CCTCC AB 2019243^T= LMG 31580^T).

Genomic insights of an alkaliphilic bacterium Halalkalibacter alkaliphilus sp. nov. isolated from an Indian Soda Lake

An alkaliphilic, Gram-stain-positive, non-motile, rod-shaped, and spore forming bacterial strain (MEB205^T) was isolated from sediment sample collected from Lonar lake, India. The strain grew optimally at pH 10, NaCl concentration of 3.0% at 37 °C. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain MEB205^T belonged to the genus Halalkalibacter in the family Bacillaceae and shared the highest sequence similarity with H. okhensis Kh10-101^T (98.9%) followed by H. wakoensis N-1 ^T (98.7%). The assembled genome of strain MEB205^T has a total length of 4.8 Mb with a G + C content of 37.8%. The dDDH and OrthoANI values between strain MEB205^T and H. okhensis Kh10-101 ^T were 29.1% and 84.3%, respectively. Furthermore, the genome analysis revealed the presence of antiporter genes (nhaA and nhaD) and L-ectoine biosynthesis gene required for survival of the strain MEB205^T in alkaline-saline habitat. The major fatty acid was C_15:0 anteiso, C_16:0 and C_15:0 iso (> 10.0%). Diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine were the major polar lipids. meso-diaminopimelic acid was diagnostic diamino acid for cell wall peptidoglycan. Based on the polyphasic taxonomic studies, strain MEB205^T represent a novel species of the genus Halalkalibacter for which the name Halalkalibacter alkaliphilus sp. nov. (Type strain MEB205^T = MCC 3863 ^T = JCM 34004 ^T = NCIMB 15406 ^T) is proposed.

An Update on Novel Taxa and Revised Taxonomic Status of Bacteria (Including Members of the Phylum Planctomycetota) Isolated from Aquatic Host Species Described in 2018 to 2021

Increased interest in farmed aquatic species, aquatic conservation measures, and microbial metabolic end-product utilization have translated into a need for awareness and recognition of novel microbial species and revisions to bacterial taxonomy. Because this need has largely been unmet, through a 4-year literature review, we present lists of novel and revised bacterial species (including members of the phylum Planctomycetota) derived from aquatic hosts that can serve as a baseline for future biennial summaries of taxonomic revisions in this field. Most new and revised taxa were noted within oxidase-positive and/or nonglucose fermentative Gram-negative bacilli, including members of the Tenacibaculum, Flavobacterium, and Vibrio genera. Valid and effectively published novel members of the Streptococcus, Erysipelothrix, and Photobacterium genera are additionally described from disease pathogenesis perspectives.

Characteristics of the ErmK Protein of Bacillus halodurans C-125

Bacillus halodurans C-125 is an alkaliphilic microorganism that grows best at pH 10 to 10.5. B. halodurans C-125 harbors the erm (erythromycin resistance methylase) gene as well as the mphB (macrolide phosphotransferase) and putative mef (macrolide efflux) genes, which confer resistance to macrolide, lincosamide, and streptogramin B (MLSB) antibiotics. The Erm protein expressed in B. halodurans C-125 could be classified as ErmK because it shares 66.2% and 61.2% amino acid sequence identity with the closest ErmD and Erm(34), respectively. ErmK can be regarded as a dimethylase, as evidenced by reverse transcriptase analysis and the antibiotic resistance profile exhibited by E. coli expressing ermK. Although ErmK showed one-third or less in vitro methylating activity compared to ErmC', E. coli cells expressing ErmK exhibited comparable resistance to erythromycin and tylosin, and a similar dimethylation proportion of 23S rRNA due to the higher expression rate in a T7 promoter-mediated expression system. The less efficient methylation activity of ErmK might reflect an adaption to mitigate the fitness cost caused by dimethylation through the Erm protein presumably because B. halodurans C-125 has less probability to encounter the antibiotics in its favorable growth conditions and grows retardedly in neutral environments. IMPORTANCE Erm proteins confer MLSB antibiotic resistance (minimal inhibitory concentration [MIC] value up to 4,096 μg/mL) on microorganisms ranging from antibiotic producers to pathogens, imposing one of the most pressing threats to clinics. Therefore, Erm proteins have long been speculated to be plausible targets for developing inhibitor(s). In our laboratory, it has been noticed that there are variations in enzymatic activity among the Erm proteins, Erm in antibiotic producers being better than that in pathogens. In this study, it has been observed that Erm protein in B. halodurans C-125 extremophile is a novel member of Erm protein and acts more laggardly, compared to that in pathogen. While this sluggishness of Erm protein in extremophile might be evolved to reduce the fitness cost incurred by Erm activity adapting to its environments, this feature could be exploited to develop the more potent and/or efficacious drug to combat formidably problematic antibiotic-resistant pathogens.