The underlying mechanisms of genetic innovation and speciation in the family Corynebacteriaceae: A phylogenomics approach

Timeframe of aerobic biodegradation of bioplastics differs under standard conditions and conditions simulating technological composting with biowaste

To determine the actual timeframe of biodegradation, bioplastics (BPs) (based on polylactic acid (PLA), starch (FS), polybutylene succinate (PBS), cellulose (Cel)) were degraded with biowaste (B), which simulates real substrate technological conditions during composting. For comparison, standard conditions (with mature compost (C)) were also applied. The 90-day aerobic tests, both with C or B, were carried out at 58 ± 2 °C. This comparison enables understanding of how BPs behave in real substrate conditions and how C and B affect the time or completeness of degradation based on oxygen consumption (OC) for BPs, the ratio of OC to theoretical oxygen consumption (OC/Th-O2), and the decrease in volatile solids (VS). Additionally, for deeper insight into the biodegradation process, microscopic, microbial (based on 16S rDNA), FTIR, and mechanical (tensile strength, elongation at break) analyses were performed. There was no association between the initial mechanical properties of BPs and the time necessary for their biodegradation. BPs lost their mechanical properties and remained visible for a shorter time when degraded with C than with B. OC for Cel, FS, PLA, and PBS biodegradation was 1143, 1654, 1748, and 1211g O2/kg, respectively, which amounted to 83, 70, 69, and 60% of the theoretical OC (Th-O2), respectively. Intensive OC took place at the same time as an intensive decrease in VS content. With C, Cel was most susceptible to biodegradation (completely biodegrading within 11 days), and PLA was least susceptible (requiring 70 days for complete biodegradation). With B, however, the time required for biodegradation was generally longer, and the differences in the time needed for complete biodegradation were smaller, ranging from 45 d (FS) to 75 d (PLA). The use of C or B had the greatest effect on Cel biodegradation (10 d vs 62 d, respectively), and the least effect on PLA (70 d vs 75 d). Specific bacterial and fungal community structures were identified as potential BP biodegraders; the communities depended on the type of BPs and the substrate conditions. In conclusion, the time needed for biodegradation of these BPs varied widely depending on the specific bioplastic and the substrate conditions; the biodegradability decreased in the following order: Cel ≫ FS ≫ PBS ≫ PLA with C and FS ≫ Cel = PBS ≫ PLA with B. The biodegradability ranking of BPs with B was assumed to be ultimate as it simulates the real substrate conditions during composting. However, all of the BPs completely biodegraded in less than 90 days.

The gut microbiome from middle-aged women with depression modulates depressive-like behaviors and plasma fatty acid metabolism in female middle-aged mice

BACKGROUND

Intestinal dysbacteriosis has frequently been involved in the context of depression. Nonetheless, only scant information is available about the features and functional changes of gut microbiota in female middle-aged depression (MAD).

OBJECTIVE

This study aims to explore whether there are characteristic changes in the gut microbes of female MAD and whether these changes are associated with depressive-like behaviors. Meanwhile, this study observed alterations in the lipid metabolism function of gut microbes and further examined changes in plasma medium- and long-chain fatty acids (MLCFAs) in mice that underwent fecal microbiota transplantation (FMT).

METHODS

Stool samples obtained from 31 MAD, along with 24 healthy individuals (HC) were analyzed by 16 S rRNA gene sequencing. Meanwhile, 14-month-old female C57BL/6J mice received antibiotic cocktails and then oral gavage of the microbiota suspension of MAD or HC for 3 weeks to reconstruct gut microbiota. The subsequent depressive-like behaviors, the composition of gut microbiota, as well as MLCFAs in the plasma were evaluated.

RESULTS

A noteworthy disruption in gut microbial composition in MAD individuals compared to HC was observed. Several distinct bacterial taxa, including Dorea, Butyricicoccus, and Blautia, demonstrated associations with the demographic variables. A particular microbial panel encompassing 49 genera effectively differentiated MAD patients from HC (AUC = 0.82). Fecal microbiome transplantation from MAD subjects led to depressive-like behaviors and dysfunction of plasma MLCFAs in mice.

CONCLUSIONS

These findings suggest that microbial dysbiosis is linked to the pathogenesis of MAD, and its role may be associated with the regulation of MLCFAs metabolism.

Plasmid permissiveness of wastewater microbiomes can be predicted from 16S rRNA sequences by machine learning

MOTIVATION

Wastewater treatment plants (WWTPs) harbor a dense and diverse microbial community. They constantly receive antimicrobial residues and resistant strains, and therefore provide conditions for horizontal gene transfer (HGT) of antimicrobial resistance (AMR) determinants. This facilitates the transmission of clinically important genes between, e.g. enteric and environmental bacteria, and vice versa. Despite the clinical importance, tools for predicting HGT remain underdeveloped.

RESULTS

In this study, we examined to which extent water cycle microbial community composition, as inferred by partial 16S rRNA gene sequences, can predict plasmid permissiveness, i.e. the ability of cells to receive a plasmid through conjugation, based on data from standardized filter mating assays using fluorescent bio-reporter plasmids. We leveraged a range of machine learning models for predicting the permissiveness for each taxon in the community, representing the range of hosts a plasmid is able to transfer to, for three broad host-range resistance IncP plasmids (pKJK5, pB10, and RP4). Our results indicate that the predicted permissiveness from the best performing model (random forest) showed a moderate-to-strong average correlation of 0.49 for pB10 [95% confidence interval (CI): 0.44-0.55], 0.43 for pKJK5 (0.95% CI: 0.41-0.49), and 0.53 for RP4 (0.95% CI: 0.48-0.57) with the experimental permissiveness in the unseen test dataset. Predictive phylogenetic signals occurred despite the broad host-range nature of these plasmids. Our results provide a framework that contributes to the assessment of the risk of AMR pollution in wastewater systems.

AVAILABILITY AND IMPLEMENTATION

The predictive tool is available as an application at https://github.com/DaneshMoradigaravand/PlasmidPerm.

Disrupted gut microbiota aggravates spatial memory dysfunction induced by high altitude exposure: A link between plateau environment and microbiome-gut-brain axis

Approximately 400 million people work and live in high-altitude areas and suffer from memory dysfunction worldwide. Until now, the role of the intestinal flora in plateau-induced brain damage has rarely been reported. To address this, we investigated the effect of intestinal flora on spatial memory impairment induced by high altitudes based on the microbiome-gut-brain axis theory. C57BL/6 mice were divided into three groups: control, high-altitude (HA), and high-altitude antibiotic treatment (HAA) group. The HA and HAA groups were exposed to a low-pressure oxygen chamber that simulated an altitude of 4000 m above sea level (m. a. s.l.) for 14 days, with the air pressure in the chamber set at 60-65 kPa. The results showed that spatial memory dysfunction induced by the high-altitude environment was aggravated by antibiotic treatment, manifesting as lowered escape latency and hippocampal memory-related proteins (BDNF and PSD-95). 16 S rRNA sequencing showed a remarkable separation of the ileal microbiota among the three groups. Antibiotic treatment exacerbated the reduced richness and diversity of the ileal microbiota in mice in the HA group. Lactobacillaceae were the main target bacteria and were significantly reduced in the HA group, which was exacerbated by antibiotic treatment. Meanwhile, reduced intestinal permeability and ileal immune function in mice exposed high-altitude environment was also aggravated by antibiotic treatment, as indicated by the lowered tight junction proteins and IL-1β and IFN-γ levels. Furthermore, indicator species analysis and Netshift co-analysis revealed that Lactobacillaceae (ASV11) and Corynebacteriaceae (ASV78, ASV25, and ASV47) play important roles in high-altitude exposure-induced memory dysfunction. Interestingly, ASV78 was negatively correlated with IL-1β and IFN-γ levels, indicating that ASV78 may be induced by reduced ileal immune function, which mediates high-altitude environment exposure-induced memory dysfunction. This study provides evidence that the intestinal flora is effective in preventing brain dysfunction caused by exposure to high-altitude environments, suggesting a relationship between the microbiome-gut-brain axis and altitude exposure.

Cohnella mopanensis sp. nov., a new Gram-negative bacterium isolated from soil in Xinping Mountain National Forest Park

A Gram-stain-negative, aerobic, rod-shaped bacteria strain, named YIM B01951^T, was isolated from a forest soil sample collected from Mopan Mountain National Forest Park, Xinping City, Yunnan Province, southwest PR China (101°58'06" N, 23°03'02" E). Growth occurred at 15-40 °C (optimum, 30 °C), pH 5.0-8.0 (optimum, pH 6.5) and with up to ≤ 3.0% (w/v) NaCl on Nutrient Agar plates. The results of 16S rRNA gene sequence similarity analysis showed that strain YIM B01951^T was closely related to the type strain of Cohnella arctica M9-62^T (96.5%) and Cohnella lupini RLAHU4B^T (96.3%). YIM B01951^T contains anteiso-C_15:0 and iso-C_16:0 as the major cellular fatty acids; the main polar lipids are diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), lysylphosphatidylglycerol (PGL) and five aminophospholipids (APL). The MK-7 is the major respiratory quinone and the DNA G + C content is 49.2 mol%. Based on these phenotypic, chemotaxonomic and phylogenetic analyses, strain YIM B01951^T is considered to be a novel species of the genus Cohnella, and named Cohnella mopanensis sp. nov. The type strain is YIM B01951^T (= NBRC 115331^T = KCTC 43370^T).

Caldalkalibacillus salinus sp. nov., isolated from a salt lake in Xinjiang, northwest China

A novel Gram-stain-negative, aerobic, motile and rod-shaped bacterium, designated as strain YIM B00319^T, was isolated from a sediment sample obtained from Wuzunbulake salt Lake in Xinjiang Uygur Autonomous Region, northwest China. Phylogenetic analysis based on 16S rRNA gene sequences along with the whole genome showed that strain YIM B00319^T belongs to the family Bacillaceae and was most closely related to Bacillus horti K13^T and Caldalkalibacillus mannanilyticus JCM 10596^T, with sequence similarities of 95.7% and 94.6%, respectively. The genome of strain YIM B00319^T was 3.77 Mbp with a DNA G + C content of 43%. Strain YIM B00319^T grew at 15-45 ℃, pH 7.0-9.5 and with 3-11% (w/v) NaCl. The major respiratory quinone of strain YIM B00319^T was MK-7, and the major fatty acids (> 10%) were iso-C_15:0, anteiso-C_15:0, and summed feature 3 (C_16:1 ω6c and/or C_16:1 ω7c). The main polar lipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and diphosphatidylglycerol (DPG). The cell-wall peptidoglycan contained meso-diaminopimelic acid. On the basis of the phenotypic, chemotaxonomic, genomic, and phylogenetic information, strain YIM B00319^T represents a novel species of the genus Caldalkalibacillus, for which the name Caldalkalibacillus salinus sp. nov. is proposed. The type strain is YIM B00319^T (= CGMCC 1.18750^T = NBRC 115338^T).

Viridibacillus soli sp. nov., isolated from forest soil in Ailaoshan National Nature Reserve

A Gram stain-positive, rod-shaped, and subterminal endospore-forming bacterium, designated strain YIM B01967^T, was isolated from a forest soil sample collected in Ailaoshan National Nature Reserve, Yuxi City, Xinpin county, Yunnan province, China. Strain YIM B01967^T showed the highest 16S rRNA gene sequence similarity with Viridibacillus arvi (99.1%) and Viridibacillus arenosi (98.9%). Based on the phylogenetic and 16S rRNA gene sequence results, strain YIM B01967^T was affiliated to the genus Viridibacillus. The growth of YIM B01967^T was observed at 15-35 °C (optimum, 28 °C), pH 7.0-9.0 (optimum, pH 7.5) and in the presence of 0-2% (w/v) NaCl (optimum in 2% NaCl). The cell wall sugars include ribose, glucose, arabinose, galactose, and mannose. The quinone system consisted of the major compound MK-8 and moderate amounts of MK-7. The major fatty acids (> 10%) included iso-C_15:0, anteiso-C_15:0, C_16:1 ω10c. The major polar lipids profile included DPG, PME. The cell wall peptidoglycan was most likely of the type A4α with an L-Lys-D-Asp interpeptide bridge. The genomic DNA G + C content of strain YIM B01967^T was 36.3 mol%. The ANI and digital DNA-DNA hybridization (dDDH) values between strain YIM B01967^T and Viridibacillus arvi DSM 16317 ^T, Viridibacillus arenosi DSM 16319 ^T were 61.0% and 32.1%, 60.0% and 33.1% based on the draft genome sequence. The results support the conclusion that strain YIM B01967^T represents a novel species of the genus Viridibacillus, for which the name Viridibacillus soli sp. nov., is proposed. The type strain is YIM B01967^T (= KCTC 43249 ^T = CGMCC 1.18436 ^T).

Propioniciclava soli sp. nov., isolated from forest soil, Yunnan, China, and reclassification of the genus Brevilactibacter into the genus Propioniciclava, and Brevilactibacter sinopodophylli, Brevilactibacter flavus, and Brevilactibacter coleopterorum as Propioniciclava sinopodophylli comb. nov., Propioniciclava flava comb. nov., and Propioniciclava coleopterorum comb. nov., respectively

A Gram-stain-positive, coccus-shaped, facultatively anaerobic, non-motile bacterial strain, designated YIM S02567^T, was isolated from a forest soil sample collected from Gejiu City, Yunnan Province, southwest PR China. Growth was observed at 10-45 °C, at pH 6.0-9.5, in the presence of up to 4.0% (w/v) NaCl on R2A medium. The results of 16S rRNA gene sequence similarity analysis showed that strain YIM S02567^T was most closely related to the type strain of Brevilactibacter sinopodophylli (95.4%) and Propioniciclava tarda (94.7%), and phylogenetic analysis based on genome data showed that strain YIM S02567^T should be assigned to the genus Propioniciclava. The cell-wall diamino acid was meso-diaminopimelic acid. The major cellular fatty acids were identified as anteiso-C_15:0 and C_16:0, and the major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, and two unidentified glycolipids. The predominant menaquinone was MK-9(H₄). The genomic DNA G + C content was 71.2 mol%. Based on the polyphasic taxonomic evidence, strain YIM S02567^T is assigned to a novel member of the genus Propioniciclava, for which the name Propioniciclava soli sp. nov., (type strain YIM S02567^T = CCTCC AB 2020128^T = CGMCC 1.18504^T = KCTC 49478^T) is proposed. Furthermore, we propose the reclassification of Brevilactibacter as Propioniciclava gen. nov.

Qaidamihabitans albus gen. nov., sp. nov., a new member of the family Pseudonocardiaceae, and transfer of Prauserella shujinwangii to Qaidamihabitans gen. nov. as Qaidamihabitans shujinwangii comb. nov

A novel mycelium-forming actinomycete strain, designated YIM S01255^T were isolated from a salt lake. Optimal growth occurred in the presence of 0-5.0% (w/v) NaCl, at pH 7.0-8.0, and at 37 °C. Strain YIM S01255^T contained meso-diaminopimelic acid as the diagnostic diamino acid, and glucose, galactose and arabinose as the whole-cell sugars. The major fatty acid (> 5.0%) were iso-C_16:0, iso-C_16:1H and iso-C_15:0. The major menaquinone were MK-9(H₄) and MK-8(H₄). The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylinositolmannoside and phosphatidylinositol. The DNA G + C content was 70.7 mol%. The 16S rRNA gene sequence of the strain showed high similarity to members of genera in the family Pseudonocardiaceae with values less than 95.8%, and most closely related to the genus Amycolatopsis. Both of phylogenetic analysis based on 16S rRNA gene sequences and the up-to-date bacterial genome sequences analysis revealed that strains YIM S01255^T and Prauserella shujinwangii XJ46^T formed a distinct monophyletic clade and was separated from the other members within the family Pseudonocardiaceae. The average nucleotide identity (ANI) values and digital DNA-DNA hybridization (dDDH) between the two strains were 81.0% and 40.6%, respectively. The distinctive polyphasic evidences differentiated YIM S01255^T from members of the family Pseudonocardiaceae, so strain YIM S01255^T is considered to represent a novel species of a novel genus of the family Pseudonocardiaceae, for which the name Qaidamihabitans albus gen. nov., sp. nov. is proposed. The type strain of genus Qaidamihabitans is YIM S01255^T (= KCTC 49476^T = CGMCC 4.7684^T). Moreover, Prauserella shujinwangii is also proposed to being transferred into the genus Qaidamihabitans as Qaidamihabitans shujinwangii comb. nov. (type strain XJ46^T = CGMCC 4.7125^T = JCM 19736^T).

Glycomyces salinus sp. nov., an actinomycete isolated from a hypersaline habitat

A Gram-stain-positive, aerobic, nonmotile actinobacterium, designated strain YIM 93776^T, was isolated from a saline sediment sample collected from Aiding Lake in Xinjiang Uygur Autonomous Region, Northwest China. Phylogenetic analysis based on the 16S rRNA gene sequences showed that strain YIM 93776^T was affiliated to the genus Glycomyces and was closely related to Glycomyces albus TRM 49136^T (97.6% sequence similarity), Glycomyces lacisalsi XHU 5089^T (97.0%) and Glycomyces anabasis EGI 6500139^T (96.2%). The cell wall contained meso-diaminopimelic acid and the whole-cell hydrolysates sugars were galactose, mannose, arabinase, glucose and ribose. The predominant menaquinones were MK-9 (H₄) and MK-10 (H₄). Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, two phosphatidylglyceride, two unidentified phospholipids and two unidentified polar lipids were detected in the polar lipid extracts. Major fatty acids were anteiso-C_17:0, iso-C_15:0, iso-C_16:0, anteiso-C_15:0 and anteiso C_17:1 A. The draft genome sequence of strain YIM 93776^T was 5.37 Mbp in size with 69.5% DNA G + C content. The dDDH and ANI values between strain YIM 93776^T and related neighbours were 25.0-34.3% and 77.3-79.8%, respectively. On the basis of morphological, chemotaxonomic and phylogenetic evidence, strain YIM 93776^T; therefore, represents a novel species, for which the name Glycomyces salinus sp. nov. is proposed. The type strain is YIM 93776^T (= KCTC 49430^T = CGMCC 4.7685^T).

Effects of dicopper oxide and copper sulfate on growth performance and gut microbiota in broilers

An experiment was conducted to determine the effects of two sources of copper (Cu) from copper sulfate (CuSO4) and dicopper oxide (Cu2O, CoRouge) at three levels of inclusion (15, 75, and 150 mg/kg) on growth performance and gut microbiota of broilers. A total of 840 one-d-old male chickens (Ross 308) were weighed and randomly allocated to seven dietary treatments: negative control (NC, a basal diet without Cu addition), and the NC supplemented with 15, 75, or 150 mg Cu/kg from CuSO4 or Cu2O (12 replicate pens/treatment, 10 chicks per pen). Broilers were challenged by reusing an old litter with high concentrations in Clostridium perfringens to promote necrotic enteritis. Broiler performance was registered at d 21, 35, and 42. Excreta samples were collected at d 14, 28, and 42 for antimicrobial resistance (AMR) analyses. At d 43, one broiler per pen was euthanized to obtain ileal content for microbial characterization. Body weight d 35 and daily gain d 42 improved (P < 0.05) in Cu2O as Cu dose inclusion increased from 15 mg/kg to 150 mg/kg. Supplementation of 150 mg/kg of Cu from Cu2O decreased the abundance (P < 0.01) of some families such as Streptococcaceae and Corynebacteriaceae and increased the abundance (P < 0.05) of some commensal bacteria like Clostridiaceae and Peptostreptococcaceae. Phenotypic AMR was not different among treatments on d 14 and 28. Isolated Enterococcus spp. from broilers fed the NC diet on d 42 showed higher (P < 0.05) resistance to enrofloxacin, gentamicin, and chloramphenicol compared with Cu treatments. By contrast, the isolated Escherichia coli from broilers fed 150 mg/kg of Cu, either from CuSO4 or Cu2O, showed higher (P < 0.05) resistance to streptomycin and chloramphenicol compared to the NC. This study suggests that supplementing 150 mg/kg of Cu from Cu2O establishes changes in the gut microbiota by regulating the bacterial population in the ileum, which may explain the positive impact on broilers' growth performance.

Investigation of Potential Brain Microbiome in Alzheimer's Disease: Implications of Study Bias

BACKGROUND

Dysbiotic microbiota in the gastrointestinal tract promotes and aggravates neurodegenerative disorders. Alzheimer's disease (AD) has been shown to correlate to dysbiotic bacteria and the immune, metabolic, and endocrine abnormalities associated with abnormal gut-brain-axis signaling. Recent reports also indicate that brain dysbacteriosis may play a role in AD pathogenesis.

OBJECTIVE

To evaluate the presence and differences of brain-region dependent microbiomes in control and AD subjects and the contribution of study bias.

METHODS

Two independent cohorts of postmortem AD brain samples were collected from separate locations, processed with different extraction protocols and investigated for the presence of bacterial DNA indicative of a brain microbiome with V4 16S next generation sequencing.

RESULTS

In both cohorts, few differences between the control and AD groups were observed in terms of alpha and beta diversities, phyla and genera proportions. Independent of study in both AD and control subjects the most abundant phyla were Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. Variations in beta diversity between hippocampal and cerebellum samples were observed indicating an impact of brain region on the presence of microbial DNA. Importantly, differences in alpha and beta diversities between the two independent cohorts were found indicating a significant cohort- and processing-dependent effect on the microbiome. Finally, there were cohort-specific correlations between the gut microbiome and subject demographics indicate that postmortem interval may have a significant impact on brain microbiome determination.

CONCLUSIONS

Regardless of the study bias, this study concludes that bacterial DNA can be isolated from the human brain suggesting that a brain microbiome may exist; however, more studies are required to understand the variation in AD.

Vallicoccus soli gen. nov., sp. nov., a novel actinobacterium isolated from soil, and description of Vallicoccaceae fam. nov., Motilibacterales ord. nov

A novel Gram-stain-positive, aerobic, cocci-shaped actinobacterium, designated YIM 75000^T, was isolated from a soil sample collected from a dry-hot river valley in Yunnan Province, P.R. China. Growth was observed at 10-45 °C (optimal 37 °C), 0-8% (w/v) NaCl (optimal at 0-3% NaCl) and pH 6.0-8.0 (optimal at pH 7.3). The peptidoglycan contained LL-diaminopimelic acid, glycine, glutamic acid as well as alanine and its type was A3γ with an LL-Dpm-Gly interpeptide bridge. The major cellular fatty acids (> 10%) were C_16:0, Summed In Feature 3 (C_16:1 ω6c/C_16:1 ω7c) and C_17:1 ω8c. The predominant menaquinone was MK-9(H₄). The major whole-cell sugars contained rhamnose, ribose, arabinose and mannose. The DNA G+C content was 77.0 mol%. The 16S rRNA gene sequence similarities of strain YIM 75000^T with other species were less than 94%. Phylogenetic analyses based on 16S rRNA gene sequences and genome data, revealed that strain YIM 75000^T together with the genus Motilibacter formed a distinct phylogenetic lineage within the phylum Actinobacteria, separating them from members of all orders. Strain YIM 75000^T showed 73.4-73.7% average nucleotide identity and 19.5-19.7% digital DNA-DNA hybridization identity with the closely related genus Motilibacter. Based on the phenotypic, phylogenetic and chemotaxonomic data, it is proposed that the new isolate represents the nomenclature type of the novel species Vallicoccus soli gen. nov., sp. nov. (YIM 75000^T = DSM 45377^T = KCTC 49228^T = CGMCC 1.13844^T) which is the nomenclature type of the novel genus Vallicoccus gen. nov. within Vallicoccaceae fam. nov and Motilibacterales ord. nov in the phylum Actinobacteria. The family Vallicoccaceae fam. nov. and the order Motilibacterales (contains Vallicoccaceae fam. nov. and Motilibacteraceae Lee 2013) ord. nov. are formally proposed.

Plasmids Related to the Symbiotic Nitrogen Fixation Are Not Only Cooperated Functionally but Also May Have Evolved over a Time Span in Family Rhizobiaceae

Rhizobia are soil bacteria capable of forming symbiotic nitrogen-fixing nodules associated with leguminous plants. In fast-growing legume-nodulating rhizobia, such as the species in the family Rhizobiaceae, the symbiotic plasmid is the main genetic basis for nitrogen-fixing symbiosis, and is susceptible to horizontal gene transfer. To further understand the symbioses evolution in Rhizobiaceae, we analyzed the pan-genome of this family based on 92 genomes of type/reference strains and reconstructed its phylogeny using a phylogenomics approach. Intriguingly, although the genetic expansion that occurred in chromosomal regions was the main reason for the high proportion of low-frequency flexible gene families in the pan-genome, gene gain events associated with accessory plasmids introduced more genes into the genomes of nitrogen-fixing species. For symbiotic plasmids, although horizontal gene transfer frequently occurred, transfer may be impeded by, such as, the host’s physical isolation and soil conditions, even among phylogenetically close species. During coevolution with leguminous hosts, the plasmid system, including accessory and symbiotic plasmids, may have evolved over a time span, and provided rhizobial species with the ability to adapt to various environmental conditions and helped them achieve nitrogen fixation. These findings provide new insights into the phylogeny of Rhizobiaceae and advance our understanding of the evolution of symbiotic nitrogen fixation.

Comparative Genomic Data Provide New Insight on the Evolution of Pathogenicity in Sporothrix Species

Sporothrix species are commonly isolated from environmental and clinical samples. As common causes of zoonotic mycosis, Sporothrix species may result in localized or disseminated infections, posing considerable threat to animal and human health. However, the pathogenic profiles of different Sporothrix species varied, in virulence, geographic location and host ranges, which have yet to be explored. Analysing the genomes of Sporothrix species are useful for understanding their pathogenicity. In this study, we analyzed the whole genome of 12 Sporothrix species and six S. globosa isolates from different clinical samples in China. By combining comparative analyses with Kyoto Encyclopedia of Genes and Genomes (KEGG), Carbohydrate-Active enZymes (CAZy), antiSMASH, Pfam, and PHI annotations, Sporothrix species showed exuberant primary and secondary metabolism processes. The genome sizes of four main clinical species, i.e., S. brasiliensis, S. schenckii, S. globosa, and S. luriei were significantly smaller than other environmental and clinical Sporothrix species. The contracted genes included mostly CAZymes and peptidases genes that were usually associated with the decay of plants, as well as the genes that were associated with the loss of pathogenicity and the reduced virulence. Our results could, to some extent, explain a habitat shift of Sporothrix species from a saprobic life in plant materials to a pathogenic life in mammals and the increased pathogenicity during the evolution. Gene clusters of melanin and clavaric acid were identified in this study, which improved our understanding on their pathogenicity and possible antitumor effects. Moreover, our analyses revealed no significant genomic variations among different clinical isolates of S. globosa from different regions in China.

Population genomics of Vibrionaceae isolated from an endangered oasis reveals local adaptation after an environmental perturbation

Background

In bacteria, pan-genomes are the result of an evolutionary “tug of war” between selection and horizontal gene transfer (HGT). High rates of HGT increase the genetic pool and the effective population size (N_e), resulting in open pan-genomes. In contrast, selective pressures can lead to local adaptation by purging the variation introduced by HGT and mutation, resulting in closed pan-genomes and clonal lineages. In this study, we explored both hypotheses, elucidating the pan-genome of Vibrionaceae isolates after a perturbation event in the endangered oasis of Cuatro Ciénegas Basin (CCB), Mexico, and looking for signals of adaptation to the environments in their genomes.

Results

We obtained 42 genomes of Vibrionaceae distributed in six lineages, two of them did not showed any close reference strain in databases. Five of the lineages showed closed pan-genomes and were associated to either water or sediment environment; their high N_e estimates suggest that these lineages are not from a recent origin. The only clade with an open pan-genome was found in both environments and was formed by ten genetic groups with low N_e, suggesting a recent origin. The recombination and mutation estimators (r/m) ranged from 0.005 to 2.725, which are similar to oceanic Vibrionaceae estimations. However, we identified 367 gene families with signals of positive selection, most of them found in the core genome; suggesting that despite recombination, natural selection moves the Vibrionaceae CCB lineages to local adaptation, purging the genomes and keeping closed pan-genome patterns. Moreover, we identify 598 SNPs associated with an unstructured environment; some of the genes associated with these SNPs were related to sodium transport.

Conclusions

Different lines of evidence suggest that the sampled Vibrionaceae, are part of the rare biosphere usually living under famine conditions. Two of these lineages were reported for the first time. Most Vibrionaceae lineages of CCB are adapted to their micro-habitats rather than to the sampled environments. This pattern of adaptation is concordant with the association of closed pan-genomes and local adaptation.

Reconstructing the Phylogeny of Corynebacteriales while Accounting for Horizontal Gene Transfer

Horizontal gene transfer is a common mechanism in Bacteria that has contributed to the genomic content of existing organisms. Traditional methods for estimating bacterial phylogeny, however, assume only vertical inheritance in the evolution of homologous genes, which may result in errors in the estimated phylogenies. We present a new method for estimating bacterial phylogeny that accounts for the presence of genes acquired by horizontal gene transfer between genomes. The method identifies and corrects putative transferred genes in gene families, before applying a gene tree-based summary method to estimate bacterial species trees. The method was applied to estimate the phylogeny of the order Corynebacteriales, which is the largest clade in the phylum Actinobacteria. We report a collection of 14 phylogenetic trees on 360 Corynebacteriales genomes. All estimated trees display each genus as a monophyletic clade. The trees also display several relationships proposed by past studies, as well as new relevant relationships between and within the main genera of Corynebacteriales: Corynebacterium, Mycobacterium, Nocardia, Rhodococcus, and Gordonia. An implementation of the method in Python is available on GitHub at https://github.com/UdeS-CoBIUS/EXECT (last accessed April 2, 2020).

Aidingimonas lacisalsi sp. nov., isolated from a salt lake in China

A novel bacterium, XHU 5135^T, belonging to the genus Aidingimonas, was isolated from a salt lake sample collected in Xinjiang Province, north-west PR China. The isolate was Gram-stain-negative, rod-shaped and non-motile. The strain was catalase-positive and oxidase-negative. Growth occurred at NaCl concentrations of 5-25 % (optimum, 10-13 %), at 13-41 °C (35-37 °C) and at pH 6.0-10.0 (pH 7.0-8.0). The predominant ubiquinone was Q-9. The major fatty acids were C_19 : 0 cyclo ω8c and C_16 : 0. The G+C content of the genomic DNA was 58.1 mol%. The affiliation of strain XHU 5135^T with the genus Aidingimonas was confirmed by 16S rRNA gene sequence comparisons. The closest type strain was Aidingimonas halophile YIM 90637^T, which showed a 16S rRNA gene sequence similarity of 97.5 %. The ANI value between XHU 5135^T and the closest type strain was 80.01 %. The estimated digital DNA-DNA hybridization estimate value between strain XHU 5135^T and the closest type strain was 22.80 %. Phenotypically, the characteristics of XHU 5135^T were shown to differ from the most closely related species, A. halophila. On the basis of the data from this polyphasic study, strain XHU 5135^T represents a novel species of the genus Aidingimonas, for which the name Aidingimonas lacisalsi sp. nov. is proposed. The type strain is strain XHU 5135^T (=CCTCC AB 2016344^T=KCTC 42945^T=DSM 104700^T).

Reclassification of 'Polyangium brachysporum' DSM 7029 as Schlegelella brevitalea sp. nov

Strain DSM 7029, isolated from a soil sample in Greece, can produce antitumour glidobactins, and has been found, as a heterologous host, to produce useful nonribosomal peptide synthetase-polyketide synthase hybrid molecules known as epothilones. This strain was originally named 'Polyangium brachysporum' of the family Polyangiaceae and the order Myxococcales. However, phylogenetic analysis of the 16S rRNA gene sequence of strain DSM 7029 indicated that it was clustered with members of Schlegelella. Significant growth occurred at 25-42 °C, pH 5.0-10.0 and in the presence of 0-0.2 % (w/v) NaCl. The predominant ubiquinone was Q-8. The major fatty acids were C_16 : 1ω7c/C_16 : 1ω6c, C_16 : 0 and C_18 : 1ω7c. The G+C content of genomic DNA was 67.51 mol%. The strain was clearly distinguishable from other neighbouring Schlegelella members and genera Caldimonas and Zhizhongheella, using phylogenetic analysis, fatty acid composition data and a range of physiological and biochemical characteristics and genome analysis. Therefore, strain DSM 7029 represents a novel species of the genus Schlegelella, for which the name Schlegelella brevitalea sp. nov. is proposed.

Bailinhaonella thermotolerans gen. nov., sp. nov., a new member of the order Streptosporangiales

A Gram-positive, aerobic, non-motile actinobacterium, designated YIM 75507^T, that was isolated from a soil sample collected from a dry-hot valley, was subjected to a polyphasic taxonomic study. The isolate formed branched hyphae and no fragmentation was found. Clustered spore chains were borne from aerial mycelium. The cell-wall peptidoglycan contained glutamic acid, alanine and meso-diaminopimelic acid. Whole-cell sugars were galactose, mannose, glucosamine, glucose and ribose. The major menaquinones were MK-9(H6), MK-9(H8) and MK-10(H6). The polar phospholipids contained phosphatidylmethylethanolamine, phosphatidylethanolamine and ninhydrin-positive phosphoglycolipid. Major fatty acids were iso-C16 : 0 and 10-methyl-C17 : 0. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YIM 75507^T formed a stable and distinct lineage clustered with the genus Sinosporangium in the family Streptosporangiaceae. The draft genome sequence of strain YIM 75507^T exhibited low average nucleotide identity to the closest related strain, Sinosporangium album CPCC 201354^T (83.97 %), well below the 95-96 % species circumscription threshold. The G+C content of the genomic DNA was 73.8 mol%. On the basis of morphological, chemotaxonomic and phylogenetic evidence, strain YIM 75507^T is assigned to a novel species of a new genus, for which the name Bailinhaonella thermotolerans gen. nov., sp. nov. is proposed. The type strain of Bailinhaonella thermotolerans is YIM 75507^T (=KCTC 49229^T=CGMCC 4.7547^T).