Microbacterium enclense sp. nov., isolated from sediment sample

Diversity and potential functional role of phyllosphere-associated actinomycetota isolated from cupuassu (Theobroma grandiflorum) leaves: implications for ecosystem dynamics and plant defense strategies

Exploring the intricate relationships between plants and their resident microorganisms is crucial not only for developing new methods to improve disease resistance and crop yields but also for understanding their co-evolutionary dynamics. Our research delves into the role of the phyllosphere-associated microbiome, especially Actinomycetota species, in enhancing pathogen resistance in Theobroma grandiflorum, or cupuassu, an agriculturally valuable Amazonian fruit tree vulnerable to witches' broom disease caused by Moniliophthora perniciosa. While breeding resistant cupuassu genotypes is a possible solution, the capacity of the Actinomycetota phylum to produce beneficial metabolites offers an alternative approach yet to be explored in this context. Utilizing advanced long-read sequencing and metagenomic analysis, we examined Actinomycetota from the phyllosphere of a disease-resistant cupuassu genotype, identifying 11 Metagenome-Assembled Genomes across eight genera. Our comparative genomic analysis uncovered 54 Biosynthetic Gene Clusters related to antitumor, antimicrobial, and plant growth-promoting activities, alongside cutinases and type VII secretion system-associated genes. These results indicate the potential of phyllosphere-associated Actinomycetota in cupuassu for inducing resistance or antagonism against pathogens. By integrating our genomic discoveries with the existing knowledge of cupuassu's defense mechanisms, we developed a model hypothesizing the synergistic or antagonistic interactions between plant and identified Actinomycetota during plant-pathogen interactions. This model offers a framework for understanding the intricate dynamics of microbial influence on plant health. In conclusion, this study underscores the significance of the phyllosphere microbiome, particularly Actinomycetota, in the broader context of harnessing microbial interactions for plant health. These findings offer valuable insights for enhancing agricultural productivity and sustainability.

The Isolation and Characterization of a Novel Psychrotolerant Cellulolytic Bacterium, Microbacterium sp. QXD-8T

Cellulolytic microorganisms play a crucial role in agricultural waste disposal. Strain QXD-8T was isolated from soil in northern China. Similarity analyses of the 16S rRNA gene, as well as the 120 conserved genes in the whole-genome sequence, indicate that it represents a novel species within the genus Microbacterium. The Microbacterium sp. QXD-8T was able to grow on the CAM plate with sodium carboxymethyl cellulose as a carbon source at 15 °C, forming a transparent hydrolysis circle after Congo red staining, even though the optimal temperature for the growth and cellulose degradation of strain QXD-8T was 28 °C. In the liquid medium, it effectively degraded cellulose and produced reducing sugars. Functional annotation revealed the presence of encoding genes for the GH5, GH6, and GH10 enzyme families with endoglucanase activity, as well as the GH1, GH3, GH39, and GH116 enzyme families with β-glucosidase activity. Additionally, two proteins in the GH6 family, one in the GH10, and two of nine proteins in the GH3 were predicted to contain a signal peptide and transmembrane region, suggesting their potential for extracellularly degrade cellulose. Based on the physiological features of the type strain QXD-8T, we propose the name Microbacterium psychrotolerans for this novel species. This study expands the diversity of psychrotolerant cellulolytic bacteria and provides a potential microbial resource for straw returning in high-latitude areas at low temperatures.

Four new Microbacterium species isolated from seaweeds and reclassification of five Microbacterium species with a proposal of Paramicrobacterium gen. nov. under a genome-based framework of the genus Microbacterium

The taxonomic relationships of 10 strains isolated from seaweeds collected from two beaches in Republic of Korea were studied by sequencing and analyses of 16S rRNA genes and whole genomes. For the construction of a more reliable and robust 16S rRNA gene phylogeny, the authentic and nearly complete 16S rRNA gene sequences of all the Microbacterium type strains were selected through pairwise comparison of the sequences contained in several public databases including the List of Prokaryotic names with Standing in Nomenclature (LPSN). The clustering of the ten study strains into five distinct groups was apparent in this single gene-based phylogenetic tree. In addition, the 16S rRNA gene sequences of a few type strains were shown to be incorrectly listed in LPSN. An overall phylogenomic clustering of the genus Microbacterium was performed with a total of 113 genomes by core genome analysis. As a result, nine major (≥ three type strains) and eight minor (two type strains) clusters were defined mostly at gene support index of 92 and mean intra-cluster OrthoANIu of >80.00%. All of the study strains were assigned to a Microbacterium liquefaciens clade and distributed further into four subclusters in the core genome-based phylogenetic tree. In vitro phenotypic assays for physiological, biochemical, and chemotaxonomic characteristics were also carried out with the ten study strains and seven closely related type strains. Comparison of the overall genomic relatedness indices (OGRI) including OrthoANIu and digital DNA-DNA hybridization supported that the study strains constituted four new species of the genus Microbacterium. In addition, some Microbacterium type strains were reclassified as members of preexisting species. Moreover, some of them were embedded in a new genus of the family Microbacteriaceae based on their distinct separation in the core genome-based phylogenetic tree and amino acid identity matrices. Based on the results here, four new species, namely, Microbacterium aurugineum sp. nov., Microbacterium croceum sp. nov., Microbacterium galbinum sp. nov., and Microbacterium sufflavum sp. nov., are described, along with the proposal of Paramicrobacterium gen. nov. containing five reclassified Microbacterium species from the "Microbacterium agarici clade", with Paramicrobacterium agarici gen. nov., comb. nov. as the type species.

Uncovering the biodiversity and biosynthetic potentials of rare actinomycetes

Background

Antibiotic resistance is on the rise, and new antibiotic research has slowed in recent years, necessitating the discovery of possibly novel microbial resources capable of producing bioactive compounds. Microbial infections are gaining resistance to existing antibiotics, emphasizing the need for novel medicinal molecules to be discovered as soon as possible. Because the possibilities of isolating undiscovered actinomycetes strains have decreased, the quest for novel products has shifted to rare actinomycetes genera from regular environments or the identification of new species identified in unusual habitats.

Main body of the abstract

The non-streptomyces actinobacteria are known as rare actinomycetes that are extremely difficult to cultivate. Rare actinomycetes are known to produce a variety of secondary metabolites with varying medicinal value. In this review, we reported the diversity of rare actinomycetes in several habitat including soil, plants, aquatic environment, caves, insects and extreme environments. We also reported some isolation methods to easily recover rare Actinobacteria from various sources guided with some procedures to identify the rare Actinobacteria isolates. Finally, we reported the biosynthetic potential of rare actinomycetes and its role in the production of unique secondary metabolites that could be used in medicine, agriculture, and industry. These microbial resources will be of interest to humanity, as antibiotics, insecticides, anticancer, antioxidants, to mention but a few.

Short conclusion

Rare actinomycetes are increasingly being investigated for new medicinal compounds that could help to address existing human health challenges such as newly emerging infectious illnesses, antibiotic resistance, and metabolic disorders. The bioactive secondary metabolites from uncommon actinomycetes are the subject of this review, which focuses on their diversity in different habitats, isolation, identification and biosynthetic potentials.

Shallow-Water Hydrothermal Vents as Natural Accelerators of Bacterial Antibiotic Resistance in Marine Coastal Areas

Environmental contamination by heavy metals (HMs) poses several indirect risks to human health, including the co-spreading of genetic traits conferring resistance to both HMs and antibiotics among micro-organisms. Microbial antibiotic resistance (AR) acquisition is enhanced at sites anthropogenically polluted by HMs, as well as in remote systems naturally enriched in HMs, such as hydrothermal vents in the deep sea. However, to date, the possible role of hydrothermal vents at shallower water depths as hot spots of microbial AR gain and spreading has not been tested, despite the higher potential risks associated with the closer vicinity of such ecosystems to coasts and human activities. In this work, we collected waters and sediments at the Panarea shallow-water hydrothermal vents, testing the presence of culturable marine bacteria and their sensitivity to antibiotics and HMs. All of the bacterial isolates showed resistance to at least one antibiotic and one HM and, most notably, 80% of them displayed multi-AR on average to 12 (min 8, max 15) different antibiotics, as well as multi-HM tolerance. We show that our isolates displayed high similarity (≥99%) to common marine bacteria, affiliating with Actinobacteria, Gammaproteobacteria, Alphaproteobacteria and Firmicutes, and all displayed wide growth ranges for temperature and salinity during in vitro physiological tests. Notably, the analysis of the genomes available in public databases for their closest relatives highlighted the lack of genes for AR, posing new questions on the origin of multi-AR acquisition in this peculiar HM-rich environment. Overall, our results point out that shallow-water hydrothermal vents may contribute to enhance AR acquisition and spreading among common marine bacteria in coastal areas, highlighting this as a focus for future research.

Microbacterium paulum sp. nov., isolated from microfiltered milk

A novel Gram-stain-positive, strictly aerobic, short rod-shaped bacterium, designated 2C^T, was isolated from freshly packaged microfiltered milk. This strain was able to grow within the NaCl concentration range of 0-5 % (w/v), temperature range of 8-37 °C (optimally at 30 °C) and at pH 6.0-10.0. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 2C^T was closely related to species of the genus Microbacterium, with the highest sequence similarity (99.2 %) to Microbacterium lacticum DSM 20427^T as well as Microbacterium flavum DSM 18909^T (=YM18-098^T). The phylogenetic tree based on 16S rRNA genes showed that strain 2C^T clustered with M. flavum DSM 18909^T. However, the phylogenetic tree based on concatenated 16S rRNA and four housekeeping genes showed that strain 2C^T clustered with M. lacticum DSM 20427^T. Furthermore, the phylogenomic tree showed that strain 2C^T clustered with M. lacticum DSM 20427^T and M. flavum DSM 18909^T. The major respiratory quinones were MK-10, MK-11 and MK-12. The predominant cellular fatty acids were anteiso-C_15 : 0, iso-C_16 : 0 and anteiso-C_17 : 0. The polar lipid composition of strain 2C^T consisted of diphosphatidylglycerol, phosphatidylglycerol, three unidentified glycolipids and two unidentified lipids. The cell-wall peptidoglycan type was a variant of B1α {Gly} [l-Lys] d-Glu-l-Lys, with the amino acids lysine, glycine, alanine and glutamic acid. The whole-cell sugars consisted of galactose, glucose, ribose and minor amounts of rhamnose. In addition, strain 2C^T showed a glycolyl-type cell wall. The genomic DNA G+C content was 69.8mol%, while the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values with the closely related Microbacterium species were below the recognized thresholds of 95-96 % ANI and 70 % DDH for species definition. Based on the phenotypic and genotypic data, strain 2C^T (=LMG 32277^T=CECT 30329^T) is considered to represent a new species, for which the name Microbacterium paulum sp. nov. is proposed.

Microbacterium helvum sp. nov., a novel actinobacterium isolated from cow dung

A Gram-positive, aerobic, non-motile, non-spore-forming, short rod-shaped strain, NEAU-LLC^T, was isolated from cow dung in Shangzhi City, Heilongjiang Province, Northeast China and identified by a polyphasic taxonomic study. Colonies was light yellow, round, with entire margin. Strain NEAU-LLC^T was grown at 15-45 ℃ and pH 6.0-10.0. NaCl concentration ranged from 0 to 5% (W/V). The 16S rRNA gene sequence of NEAU-LLC^T showed the high similarities with Microbacterium kyungheense JCM 18735^T (98.5%), Microbacterium trichothecenolyticum JCM 1358^T (98.3%) and Microbacterium jejuense JCM 18734^T (98.2%). The whole-cell sugars were glucose, rhamnose and ribose. The menaquinones contained MK-12 and MK-13. Ornithine, glutamic acid, lysine and a small amount of alanine and glycine were the amino acids in the hydrolyzed products of the cell wall. The major fatty acids were iso-C_16:0, iso-C_18:0, anteiso-C_15:0 and anteiso-C_17:0. The main polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unidentified glycolipid. The genome of NEAU-LLC^T was 4,369,375 bp and G + C content is 70.28 mol%. A combination of DNA-DNA hybridization result and some phenotypic characteristics demonstrated that strain NEAU-LLC^T could be distinguished from its closely related strains. Therefore, the strain NEAU-LLC^T was considered to represent a novel species, which was named Microbacterium helvum sp. (Type strain NEAU-LLC^T = CCTCC AA 2018026^T = JCM 32661^T).

Microbial ingress and in vitro degradation enhanced by glucose on bioabsorbable Mg-Li-Ca alloy

Biodegradable magnesium alloys are challenging to be implanted in patients with hyperglycemia and diabetes. A hypothesis is suggested that glucose accelerates microbial ingress and in vitro degradation of Mg-Li-Ca implants. Corrosion resistance and mechanical properties was demonstrated using electrochemical, hydrogen evolution and tensile tests. The bacteria from Hank's solution were isolated via 16S rRNA gene analysis. The results revealed that Mg-1Li-1Ca alloy exhibited different responses to Hank's solution with and without glucose. The solution acidity was ascribed to Microbacterium hominis and Enterobacter xiangfangensis, indicating that glucose promoted microbial activity and degradation and deterioration in mechanical property of Mg-1Li-1Ca alloy.

Microbacterium protaetiae sp. nov., isolated from gut of larva of Protaetia brevitarsis seulensis

A Gram-stain-positive, strictly aerobic, polar flagellated, short rod-shaped bacterium, designated DFW100M-13T, was isolated from gut of the larva of Protaetia brevitarsis seulensis collected from Wanju-gun, South Korea. The growth range of NaCl concentration was 0–3 % (w/v) (optimally 0 % (w/v)), the temperature range for growth was 10–40 °C (optimally 28–30 °C), and the pH range for growth was pH 6.0–9.0 (optimally pH 7.0–8.0). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain DFW100M-13T had a high sequence similarity to members of the genus Microbacterium , having the highest similarity with Microbacterium luticocti DSM 19459T (97.7 %), Microbacterium rhizosphaerae CHO1T (97.1 %), and Microbacterium immunditiarum SK 18T (97.0 %), and formed a distinct lineage with Microbacterium luticocti DSM 19459T within the genus Microbacterium . A phylogenetic tree based on house-keeping genes also showed the result similar to the 16S rRNA gene-based tree. The main respiratory quinone (>10 %) was MK-11, MK-12 and MK-10, and the predominant cellular fatty acids (>10 %) were iso-C16 : 0, anteiso-C17 : 0 and anteiso-C15 : 0. The polar lipids were composed of diphosphatidylglycerol, phosphatidylglycerol, an inidentified glycolipid and an unidnetified lipid. The peptidoglycan type was supposed to be the B2ß with amino acids d-alanine, d-glutamic acid, glycine, l-homoserine and d-ornithine. The genomic DNA G+C content was 68.0 mol%. Based on the polyphasic taxonomic data, strain DFW100M-13T is considered to represent a novel species, for which the name Microbacterium protaetiae sp. nov. is proposed. The type strain is DFW100M-13T (=KACC 19323T=NBRC 113120T).

Improved Draft Genome Sequence of Microbacterium sp. Strain LKL04, a Bacterial Endophyte Associated with Switchgrass Plants

We report here the genome assembly and analysis of Microbacterium strain sp. LKL04, a Gram-positive bacterial endophyte isolated from switchgrass plants (Panicum virgatum) grown on a reclaimed coal-mining site. The 2.9-Mbp genome of this bacterium was assembled into a single contig encoding 2,806 protein coding genes.

We report here the genome assembly and analysis of Microbacterium strain sp. LKL04, a Gram-positive bacterial endophyte isolated from switchgrass plants (Panicum virgatum) grown on a reclaimed coal-mining site. The 2.9-Mbp genome of this bacterium was assembled into a single contig encoding 2,806 protein coding genes.

Marine Rare Actinomycetes: A Promising Source of Structurally Diverse and Unique Novel Natural Products

Rare actinomycetes are prolific in the marine environment; however, knowledge about their diversity, distribution and biochemistry is limited. Marine rare actinomycetes represent a rather untapped source of chemically diverse secondary metabolites and novel bioactive compounds. In this review, we aim to summarize the present knowledge on the isolation, diversity, distribution and natural product discovery of marine rare actinomycetes reported from mid-2013 to 2017. A total of 97 new species, representing 9 novel genera and belonging to 27 families of marine rare actinomycetes have been reported, with the highest numbers of novel isolates from the families Pseudonocardiaceae, Demequinaceae, Micromonosporaceae and Nocardioidaceae. Additionally, this study reviewed 167 new bioactive compounds produced by 58 different rare actinomycete species representing 24 genera. Most of the compounds produced by the marine rare actinomycetes present antibacterial, antifungal, antiparasitic, anticancer or antimalarial activities. The highest numbers of natural products were derived from the genera Nocardiopsis, Micromonospora, Salinispora and Pseudonocardia. Members of the genus Micromonospora were revealed to be the richest source of chemically diverse and unique bioactive natural products.

Genome-Based Taxonomic Classification of the Phylum Actinobacteria

The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

Microbacterium telephonicum sp. nov., isolated from the screen of a cellular phone

A cultivation-based study of the microbial diversity of cellular phone screens led to the isolation of a Gram-stain-positive, aerobic, rod-shaped and non-endospore-forming bacterium, designated S2T63^T, exhibiting phenotypic and genotypic characteristics unique to the type strains of closely related species. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain is a member of Microbacterium, and most closely related to Microbacterium aurantiacum IFO 15234^T and Microbacterium kitamiense Kitami C2^T. The DNA-DNA relatedness values of the strain S2T63^T to M. aurantiacum KACC 20510^T, M. kitamiense KACC 20514^Tand Microbacterium laevaniformans KACC 14463^T were 65 % (±4), 29.5 % (±3) and 55.9 % (±4), respectively. The genomic DNA G+C content was 71.8 mol%. The major fatty acids were anteiso-C15 : 0, iso-C16 : 0, C16 : 0 and anteiso-C17 : 0. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and two unidentified polar lipids. The peptidoglycan contained the amino acids glycine, lysine, alanine and glutamic acid, with substantial amounts of hydroxy glutamic acid detected, which is characteristic of peptidoglycan type B1α. The predominant menaquinones were MK-12 and MK-13. Rhamnose, fucose and galactose were the whole-cell sugars detected. The strain also showed biofilm production, estimated by using crystal violet assay. Based on the results of the phenotypic and genotypic characterizations, it was concluded that the new strain represents a novel species of the genus Microbacterium, for which the name Microbacteriumtelephonicum is proposed, with S2T63T (=MCC 2967^T=KACC 18715^T=LMG 29293^T) as the type strain.

Draft Genome Sequence of Microbacterium oleivorans Strain A9, a Bacterium Isolated from Chernobyl Radionuclide-Contaminated Soil

Here, we present the draft genome sequence of Microbacterium oleivorans strain A9, a uranium-tolerant actinobacterium which has been isolated from radionuclide-contaminated soil from the Chernobyl exclusion zone. It is composed of 22 contigs totaling 2,954,335 bp and contains 2,813 coding DNA sequences, one cluster of rRNA genes, and 45 tRNA genes.

Microbacterium zeae sp. nov., an endophytic bacterium isolated from maize stem

A novel Gram-stain positive, aerobic, non-motile, non-spore-forming and rod-shaped strain designated 1204^T was isolated from surface-sterilised stem tissue of maize planted in Fangshan District of Beijing, People's Republic of China. A polyphasic taxonomic study was performed on the new isolate. On the basis of 16S rRNA gene sequence similarity studies, this isolate belongs to the genus Microbacterium. High levels of 16S rRNA gene sequence similarity were found between strain 1204^T and Microbacterium enclense NIO-1002^T (98.8%) and Microbacterium proteolyticum RZ36^T (98.4%) respectively. However, the DNA-DNA hybridization values between strain 1204^T and its closely related species M. proteolyticum DSM 27100^T and M. enclense DSM 25125^T were 53.9 ± 1.6 and 20.9 ± 1.5% respectively. The DNA G+C content of strain 1204^T was determined to be 68.0 mol%. The major fatty acids were found to consist of anteiso-C_15:0 (37.6%), iso-C_16:0 (28.6%) and anteiso-C_17:0 (16.6%). The predominant menaquinone was MK-11 and the polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, an unidentified glycolipid and an unidentified lipid. The results of physiological and biochemical tests and minor differences in the fatty acid profiles allowed a clear phenotypic differentiation of strain 1204^T from the closely related species in the genus Microbacterium. Thus, it was concluded that strain 1204^T represents a novel species within the genus Microbacterium, for which the name Microbacterium zeae sp. nov. is proposed, with the type strain 1204^T (= CGMCC 1.15289 = DSM 100750).

Structural Characterization of a Novel Antioxidant Pigment Produced by a Photochromogenic Microbacterium oxydans Strain

The Microbacteriaceae family, such as Microbacterium, is well known for its ability to produce carotenoid-type pigments, but little has been published on the structure of such pigments. Here, we isolated the yellow pigment that is responsible for the yellowish color of a Microbacterium oxydans strain isolated from a decomposing stump of a resinous tree. The pigment, which is synthesized when the bacterium is grown under light, was purified and characterized using several spectroscopic analyses, such as ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (¹H NMR, ¹³C NMR), and high-resolution mass spectrometry (HRMS). From these analysis, a molecular formula (C₂₇H₄₂O₂) and a chemical structure (8-hydroxymethyl-2,4,12-trimethyl-14-(2,6,6-trimethyl-cyclohex-2-enyl)-teradeca-3,7,9,11,13-pentan-2-ol) were deduced. The chemical properties of the pigment, such as aqueous stability at different pH, stability in different organic solvents, and antioxidant capacity, are also reported. Together, these data and previous studies have resulted in the identification of a new antioxidant pigment produced by M. oxydans. To the best of our knowledge, this is the first thorough investigation of this carotenoid-like pigment in the Microbacterium genera.