Pan-genome dynamics of Pseudomonas gene complements enriched across hexachlorocyclohexane dumpsite

Adaptive evolution of Sphingopyxis sp. MC4 conferred degradation potential for persistent β- and δ-Hexachlorocyclohexane (HCH) isomers

Hexachlorocyclohexane (HCH), an organochlorine pesticide imposes several harmful impacts on the ecosystem. β- and δ-isomers of HCH are highly toxic, persistent, and recalcitrant to biodegradation, slow and incomplete degradation of β- and δ- isomers have been reported in a few strains. We have isolated a strain designated as Sphingopyxis strain MC4 that can tolerate and degrade high concentrations of α-, β-, γ- and δ-HCH isomers. To date, no other Sphingopyxis strain has been reported to degrade β- and δ-isomers. To understand the underlying genetic makeup contributing to adaptations, the whole genome of strain MC4 was sequenced. Comparative genome analysis showed that strain MC4 harbors the complete pathway (lin genes) required for HCH degradation. Genetic footprints such as presence of lin genes on genomic islands, IS6100 elements in close proximity of lin genes, and synteny in lin flanking regions with other strains reflects the horizontal gene transfer in strain MC4. Positive selection and HGT drive the adaptive evolution of strain MC4 under the pressure of HCH contamination that it experienced in its surrounding niche. In silico analyses showed efficient binding of β- and δ-isomers with enzymes leading to rapid degradation that need further validation by cloning and biochemical experiments.

Phylogenetic Relationships and Potential Functional Attributes of the Genus Parapedobacter: A Member of Family Sphingobacteriaceae

The genus Parapedobacter was established to describe a novel genus within the family Sphingobacteriaceae and derives its name from Pedobacter, with which it is shown to be evolutionarily related. Despite this, Parapedobacter and Pedobacter do not share very high 16S rRNA gene sequence similarities. Therefore, we hypothesized whether these substantial differences at the 16S rRNA gene level depict the true phylogeny or that these genomes have actually diverged. Thus, we performed genomic analysis of the four available genomes of Parapedobacter to better understand their phylogenomic position within family Sphingobacteriaceae. Our results demonstrated that Parapedobacter is more closely related to species of Olivibacter, as opposed to the genus Pedobacter. Further, we identified a significant class of enzymes called pectinases with potential industrial applications within the genomes of Parapedobacter luteus DSM 22899^T and Parapedobacter composti DSM 22900^T. These enzymes, specifically pectinesterases and pectate lyases, are presumed to have largely different catalytic activities based on very low sequence similarities to already known enzymes and thus may be exploited for industrial applications. We also determined the complete Bacteroides aerotolerance (Bat) operon (batA, batB, batC, batD, batE, hypothetical protein, moxR, and pa3071) within the genome of Parapedobacter indicus RK1^T. This expands the definition of genus Parapedobacter to containing members that are able to tolerate oxygen stress using encoded oxidative stress responsive systems. By conducting a signal propagation network analysis, we determined that BatD, BatE, and hypothetical proteins are the major controlling hubs that drive the expression of Bat operon. As a key metabolic difference, we also annotated the complete iol operon within the P. indicus RK1^T genome for utilization of all three stereoisomers of inositol, namely myo-inositol, scyllo-inositol, and 1D-chiro-inositol, which are abundant sources of organic phosphate found in soils. The results suggest that the genus Parapedobacter holds promising applications owing to its environmentally relevant genomic adaptations, which may be exploited in the future.

Complete genome sequence of Paracoccus sp. strain AK26: Insights into multipartite genome architecture and methylotropy

The present study reports the functional annotation of complete genome of methylotrophic bacterium Paracoccus sp. strain AK26. The 3.6 Mb genome with average GC content of 65.7% was distributed across five replicons; including chromosome (2.7 Mb) and four extrachromosomal replicons pAK1 (471Kb), pAK2 (189Kb), pAK3 (129Kb) and pAK4 (84 Kb). Interestingly, nearly 23% of the Cluster of Orthologous Group (COG) of proteins were annotated on extrachromosomal replicons and 185Kb genome content was attributed to segregated 19 genomic island regions. Among the four replicons, pAK4 was identified as essential and integral part of the genome, as supported by codon usage, GC content (66%) and synteny analysis. Comparative genome analysis for methylotrophy showed mechanistic variations in oxidation and assimilation of C1 compounds among closely related Paracoccus spp. Collectively, present study reports the functional characterization and genomic architecture of strain AK26 and provides genetic basis for quinone and isoprenoid based secondary metabolites synthesis using strain AK26.

Defining the Environmental Adaptations of Genus Devosia: Insights into its Expansive Short Peptide Transport System and Positively Selected Genes

Devosia are well known for their dominance in soil habitats contaminated with various toxins and are best characterized for their bioremediation potential. In this study, we compared the genomes of 27 strains of Devosia with aim to understand their metabolic abilities. The analysis revealed their adaptive gene repertoire which was bared from 52% unique pan-gene content. A striking feature of all genomes was the abundance of oligo- and di-peptide permeases (oppABCDF and dppABCDF) with each genome harboring an average of 60.7 ± 19.1 and 36.5 ± 10.6 operon associated genes respectively. Apart from their primary role in nutrition, these permeases may help Devosia to sense environmental signals and in chemotaxis at stressed habitats. Through sequence similarity network analyses, we identified 29 Opp and 19 Dpp sequences that shared very little homology with any other sequence suggesting an expansive short peptidic transport system within Devosia. The substrate determining components of these permeases viz. OppA and DppA further displayed a large diversity that separated into 12 and 9 homologous clusters respectively in addition to large number of isolated nodes. We also dissected the genome scale positive evolution and found genes associated with growth (exopolyphosphatase, HesB_IscA_SufA family protein), detoxification (moeB, nifU-like domain protein, alpha/beta hydrolase), chemotaxis (cheB, luxR) and stress response (phoQ, uspA, luxR, sufE) were positively selected. The study highlights the genomic plasticity of the Devosia spp. for conferring adaptation, bioremediation and the potential to utilize a wide range of substrates. The widespread toxin-antitoxin loci and ‘open’ state of the pangenome provided evidence of plastic genomes and a much larger genetic repertoire of the genus which is yet uncovered.

Taxonomically Characterized and Validated Bacterial Species Based on 16S rRNA Gene Sequences from India During the Last Decade

Microbial taxonomy dealing with identification and characterization of prokaryotes like bacteria and archaea has always been a major area of research all over the world. Exploring diversity of microbes and description of novel species with different genes and secondary compounds is of utmost importance for better future and sustenance of life. India having an enormous range of ecosystems and diverse species inhabiting these niches is considered to be one of the richest biodiversity regions of the world. During the last decade, with newer methodologies and better technology, the prokaryotic taxonomy from India has extended our inventory of microbial communities in specific niches. However, there still exist some limitations in classifying the microbes from India as compared to that is done world-over. This review enlists the taxonomic description of novel taxa of prokaryotes from India in the past decade. A total of 378 new bacterial species have been classified from different habitats in India in the last ten years and no descriptions of archaeal species is documented till date.

Genomic Analysis of Pseudomonas sp. Strain SCT, an Iodate-Reducing Bacterium Isolated from Marine Sediment, Reveals a Possible Use for Bioremediation

Strain SCT is an iodate-reducing bacterium isolated from marine sediment in Kanagawa Prefecture, Japan. In this study, we determined the draft genome sequence of strain SCT and compared it to complete genome sequences of other closely related bacteria, including Pseudomonas stutzeri. A phylogeny inferred from concatenation of core genes revealed that strain SCT was closely related to marine isolates of P. stutzeri. Genes present in the SCT genome but absent from the other analyzed P. stutzeri genomes comprised clusters corresponding to putative prophage regions and possible operons. They included pil genes, which encode type IV pili for natural transformation; the mer operon, which encodes resistance systems for mercury; and the pst operon, which encodes a Pi-specific transport system for phosphate uptake. We found that strain SCT had more prophage-like genes than the other P. stutzeri strains and that the majority (70%) of them were SCT strain-specific. These genes, encoded on distinct prophage regions, may have been acquired after branching from a common ancestor following independent phage transfer events. Thus, the genome sequence of Pseudomonas sp. strain SCT can provide detailed insights into its metabolic potential and the evolution of genetic elements associated with its unique phenotype.

Genome Mining and Predictive Functional Profiling of Acidophilic Rhizobacterium Pseudomonas fluorescens Pt14

Pseudomonas fluorescens Pt14 is a non-pathogenic and acidophilic bacterium isolated from acidic soil (pH 4.65). Genome sequencing of strain Pt14 was performed using Single Molecule Real Time (SMRT) sequencing to get insights into unique existence of this strain in acidic environment. Complete genome sequence of this strain revealed a chromosome of 5,841,722 bp having 5354 CDSs and 88 RNAs. Phylogenomic reconstruction based on 16S rRNA gene, Average Nucleotide Identity (ANI) values and marker proteins revealed that strain Pt14 shared a common clade with P. fluorescens strain A506 and strain SS101. ANI value of strain Pt14 in relation to strain A506 was found 99.23% demonstrating a very close sub-species association at genome level. Further, orthology determination among these three phylogenetic neighbors revealed 4726 core proteins. Functional analysis elucidated significantly higher abundance of sulphur metabolism (>1×) which could be one of the reasons for the survival of strain Pt14 under acidic conditions (pH 4.65). Acidophilic bacteria have capability to oxidize sulphur into sulphuric acid which in turn can make the soil acidic and genome-wide analysis of P. fluorescens Pt14 demonstrated that this strain contributes towards making the soil acidic.

Environmental Pseudomonads Inhibit Cystic Fibrosis Patient-Derived Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen which is evolving resistance to many currently used antibiotics. While much research has been devoted to the roles of pathogenic P. aeruginosa in cystic fibrosis (CF) patients, less is known of its ecological properties. P. aeruginosa dominates the lungs during chronic infection in CF patients, yet its abundance in some environments is less than that of other diverse groups of pseudomonads. Here, we sought to determine if clinical isolates of P. aeruginosa are vulnerable to environmental pseudomonads that dominate soil and water habitats in one-to-one competitions which may provide a source of inhibitory factors. We isolated a total of 330 pseudomonads from diverse habitats of soil and freshwater ecosystems and competed these strains against one another to determine their capacity for antagonistic activity. Over 900 individual inhibitory events were observed. Extending the analysis to P. aeruginosa isolates revealed that clinical isolates, including ones with increased alginate production, were susceptible to competition by multiple environmental strains. We performed transposon mutagenesis on one isolate and identified an ∼14.8-kb locus involved in antagonistic activity. Only two other environmental isolates were observed to carry the locus, suggesting the presence of additional unique compounds or interactions among other isolates involved in outcompeting P. aeruginosa. This collection of strains represents a source of compounds that are active against multiple pathogenic strains. With the evolution of resistance of P. aeruginosa to currently used antibiotics, these environmental strains provide opportunities for novel compound discovery against drug-resistant clinical strains.

IMPORTANCE We demonstrate that clinical CF-derived isolates of P. aeruginosa are susceptible to competition in the presence of environmental pseudomonads. We observed that many diverse environmental strains exhibited varied antagonistic profiles against a panel of clinical P. aeruginosa isolates, suggesting the presence of distinct mechanisms of inhibition among these ecological strains. Understanding the properties of these antagonistic events offers the potential for discoveries of antimicrobial compounds or metabolic pathways important to the development of novel treatments for P. aeruginosa infections.

Survey of (Meta)genomic Approaches for Understanding Microbial Community Dynamics

Advancement in the next generation sequencing technologies has led to evolution of the field of genomics and metagenomics in a slim duration with nominal cost at precipitous higher rate. While metagenomics and genomics can be separately used to reveal the culture-independent and culture-based microbial evolution, respectively, (meta)genomics together can be used to demonstrate results at population level revealing in-depth complex community interactions for specific ecotypes. The field of metagenomics which started with answering "who is out there?" based on 16S rRNA gene has evolved immensely with the precise organismal reconstruction at species/strain level from the deeply covered metagenome data outweighing the need to isolate bacteria of which 99% are de facto non-cultivable. In this review we have underlined the appeal of metagenomic-derived genomes in providing insights into the evolutionary patterns, growth dynamics, genome/gene-specific sweeps, and durability of environmental pressures. We have demonstrated the use of culture-based genomics and environmental shotgun metagenome data together to elucidate environment specific genome modulations via metagenomic recruitments in terms of gene loss/gain, accessory and core-genome extent. We further illustrated the benefit of (meta)genomics in the understanding of infectious diseases by deducing the relationship between human microbiota and clinical microbiology. This review summarizes the technological advances in the (meta)genomic strategies using the genome and metagenome datasets together to increase the resolution of microbial population studies.

Differential Functional Constraints Cause Strain-Level Endemism in Polynucleobacter Populations

Understanding the biological factors influencing habitat-wide genetic endemism is important for explaining observed biogeographic patterns. Polynucleobacter is a genus of bacteria that seems to have found a way to colonize myriad freshwater ecosystems and by doing so has become one of the most abundant bacteria in these environments. We sequenced metagenomes from locations across the Chicago River system and assembled Polynucleobacter genomes from different sites and compared how the nucleotide composition, gene codon usage, and the ratio of synonymous (codes for the same amino acid) to nonsynonymous (codes for a different amino acid) mutations varied across these population genomes at each site. The environmental pressures at each site drove purifying selection for functional traits that maintained a streamlined core genome across the Chicago River Polynucleobacter population while allowing for site-specific genomic adaptation. These adaptations enable Polynucleobacter to become dominant across different riverine environmental gradients.

The adaptation of bacterial lineages to local environmental conditions creates the potential for broader genotypic diversity within a species, which can enable a species to dominate across ecological gradients because of niche flexibility. The genus Polynucleobacter maintains both free-living and symbiotic ecotypes and maintains an apparently ubiquitous distribution in freshwater ecosystems. Subspecies-level resolution supplemented with metagenome-derived genotype analysis revealed that differential functional constraints, not geographic distance, produce and maintain strain-level genetic conservation in Polynucleobacter populations across three geographically proximal riverine environments. Genes associated with cofactor biosynthesis and one-carbon metabolism showed habitat specificity, and protein-coding genes of unknown function and membrane transport proteins were under positive selection across each habitat. Characterized by different median ratios of nonsynonymous to synonymous evolutionary changes (dN/dS ratios) and a limited but statistically significant negative correlation between the dN/dS ratio and codon usage bias between habitats, the free-living and core genotypes were observed to be evolving under strong purifying selection pressure. Highlighting the potential role of genetic adaptation to the local environment, the two-component system protein-coding genes were highly stable (dN/dS ratio, < 0.03). These results suggest that despite the impact of the habitat on genetic diversity, and hence niche partition, strong environmental selection pressure maintains a conserved core genome for Polynucleobacter populations.

IMPORTANCE Understanding the biological factors influencing habitat-wide genetic endemism is important for explaining observed biogeographic patterns. Polynucleobacter is a genus of bacteria that seems to have found a way to colonize myriad freshwater ecosystems and by doing so has become one of the most abundant bacteria in these environments. We sequenced metagenomes from locations across the Chicago River system and assembled Polynucleobacter genomes from different sites and compared how the nucleotide composition, gene codon usage, and the ratio of synonymous (codes for the same amino acid) to nonsynonymous (codes for a different amino acid) mutations varied across these population genomes at each site. The environmental pressures at each site drove purifying selection for functional traits that maintained a streamlined core genome across the Chicago River Polynucleobacter population while allowing for site-specific genomic adaptation. These adaptations enable Polynucleobacter to become dominant across different riverine environmental gradients.

(Meta)genomic insights into the pathogenome of Cellulosimicrobium cellulans

Despite having serious clinical manifestations, Cellulosimicrobium cellulans remain under-reported with only three genome sequences available at the time of writing. Genome sequences of C. cellulans LMG16121, C. cellulans J36 and Cellulosimicrobium sp. strain MM were used to determine distribution of pathogenicity islands (PAIs) across C. cellulans, which revealed 49 potential marker genes with known association to human infections, e.g. Fic and VbhA toxin-antitoxin system. Oligonucleotide composition-based analysis of orthologous proteins (n = 791) across three genomes revealed significant negative correlation (P < 0.05) between frequency of optimal codons (F_opt) and gene G+C content, highlighting the G+C-biased gene conversion (gBGC) effect across Cellulosimicrobium strains. Bayesian molecular-clock analysis performed on three virulent PAI proteins (Fic; D-alanyl-D-alanine-carboxypeptidase; transposase) dated the divergence event at 300 million years ago from the most common recent ancestor. Synteny-based annotation of hypothetical proteins highlighted gene transfers from non-pathogenic bacteria as a key factor in the evolution of PAIs. Additonally, deciphering the metagenomic islands using strain MM’s genome with environmental data from the site of isolation (hot-spring biofilm) revealed (an)aerobic respiration as population segregation factor across the in situ cohorts. Using reference genomes and metagenomic data, our results highlight the emergence and evolution of PAIs in the genus Cellulosimicrobium.