Genome Surfing As Driver of Microbial Genomic Diversity

Assembly of 97 Novel Bacterial Genomes in the Microbial Community Affiliated with Polyvinyl Alcohol in Soil of Northern China

Background

Undeveloped ecosystems belong to rich source of microbial population, of which resources remain unearthed. A kind of polymeric compound system with high polyvinyl alcohol (PVA) content has been reported and named Taisui. Marker gene amplification showed that Taisui harbored little-explored microbial communities.

Aim

To address this issue, our study attempted to recover draft genomes and functional potential from microbial communities in Taisui using the metagenomic approach. Material and Methods. Taisui communities provided 97 novel bacterial genomes from 13 bacterial phyla, including bacteria candidate phylum. Two novel genus-level lineages were recovered from Planctomycetes and Chloroflexi. Based on the draft genomes, we expanded the number of taxa with potential productions of PKS and NRPS in phyla including Candidatus Dadabacteria, Chloroflexi, and Planctomycetes.

Results

A rich diversity of PVA dehydrogenase genes from 4 phyla, involving Proteobacteria, Acidobacteria, Acitinobacteria, and Planctomycetes, were identified. The phylogenetic tree of PVA dehydrogenase showed the possibility of horizontal gene transfer between microbes.

Conclusion

Our study underscores the substantial microbial diversity and PVA degradation potential in the previously unexplored Taisui system.

Critical Review of Polyphosphate and Polyphosphate Accumulating Organisms for Agricultural Water Quality Management

Despite ongoing management efforts, phosphorus (P) loading from agricultural landscapes continues to impair water quality. Wastewater treatment research has enhanced our knowledge of microbial mechanisms influencing P cycling, especially regarding microbes known as polyphosphate accumulating organisms (PAOs) that store P as polyphosphate (polyP) under oxic conditions and release P under anoxic conditions. However, there is limited application of PAO research to reduce agricultural P loading and improve water quality. Herein, we conducted a meta-analysis to identify articles in Web of Science on polyP and its use by PAOs across five disciplines (i.e., wastewater treatment, terrestrial, freshwater, marine, and agriculture). We also summarized research that provides preliminary support for PAO-mediated P cycling in natural habitats. Terrestrial, freshwater, marine, and agriculture disciplines had fewer polyP and PAO articles compared to wastewater treatment, with agriculture consistently having the least. Most meta-analysis articles did not overlap disciplines. We found preliminary support for PAOs in natural habitats and identified several knowledge gaps and research opportunities. There is an urgent need for interdisciplinary research linking PAOs, polyP, and oxygen availability with existing knowledge of P forms and cycling mechanisms in natural and agricultural environments to improve agricultural P management strategies and achieve water quality goals.

The biogeography of Streptomyces in New Zealand enabled by high-throughput sequencing of genus-specific rpoB amplicons

We evaluated Streptomyces biogeography in soils along a 1200 km latitudinal transect across New Zealand (NZ). Streptomyces diversity was examined using high-throughput sequencing of rpoB amplicons generated with a Streptomyces specific primer set. We detected 1287 Streptomyces rpoB operational taxonomic units (OTUs) with 159 ± 92 (average ± SD) rpoB OTUs per site. Only 12% (n = 149) of these OTUs matched rpoB sequences from cultured specimens (99% nucleotide identity cutoff). Streptomyces phylogenetic diversity (Faith's PD) was correlated with soil pH, mean annual temperature and plant community richness (Spearman's r: 0.77, 0.64 and -0.79, respectively; P < 0.05), but not with latitude. In addition, soil pH and plant community richness both explained significant variation in Streptomyces beta diversity. Streptomyces communities exhibited both high dissimilarity and strong dominance of one or a few species at each site. Taken together, these results suggest that dispersal limitation due to competitive interactions limits the colonization success of spores that relocate to new sites. Cultivated Streptomyces isolates represent a major source of clinically useful antibiotics, but only a small fraction of extant diversity within the genus have been identified and most species of Streptomyces have yet to be described.

Massive gene presence-absence variation shapes an open pan-genome in the Mediterranean mussel

BACKGROUND

The Mediterranean mussel Mytilus galloprovincialis is an ecologically and economically relevant edible marine bivalve, highly invasive and resilient to biotic and abiotic stressors causing recurrent massive mortalities in other bivalves. Although these traits have been recently linked with the maintenance of a high genetic variation within natural populations, the factors underlying the evolutionary success of this species remain unclear.

RESULTS

Here, after the assembly of a 1.28-Gb reference genome and the resequencing of 14 individuals from two independent populations, we reveal a complex pan-genomic architecture in M. galloprovincialis, with a core set of 45,000 genes plus a strikingly high number of dispensable genes (20,000) subject to presence-absence variation, which may be entirely missing in several individuals. We show that dispensable genes are associated with hemizygous genomic regions affected by structural variants, which overall account for nearly 580 Mb of DNA sequence not included in the reference genome assembly. As such, this is the first study to report the widespread occurrence of gene presence-absence variation at a whole-genome scale in the animal kingdom.

CONCLUSIONS

Dispensable genes usually belong to young and recently expanded gene families enriched in survival functions, which might be the key to explain the resilience and invasiveness of this species. This unique pan-genome architecture is characterized by dispensable genes in accessory genomic regions that exceed by orders of magnitude those observed in other metazoans, including humans, and closely mirror the open pan-genomes found in prokaryotes and in a few non-metazoan eukaryotes.

The Ingenuity of Bacterial Genomes

The genomes of bacteria contain fewer genes and substantially less noncoding DNA than those of eukaryotes, and as a result, they have much less raw material to invent new traits. Yet, bacteria are vastly more taxonomically diverse, numerically abundant, and globally successful in colonizing new habitats compared to eukaryotes. Although bacterial genomes are generally considered to be optimized for efficient growth and rapid adaptation, nonadaptive processes have played a major role in shaping the size, contents, and compact organization of bacterial genomes and have allowed the establishment of deleterious traits that serve as the raw materials for genetic innovation.

Reusable building blocks in biological systems

One of the most widely recognized features of biological systems is their modularity. The modules that constitute biological systems are said to be redeployed and combined across several conditions, thus acting as building blocks. In this work, we analyse to what extent are these building blocks reusable as compared with those found in randomized versions of a system. We develop a notion of decompositions of systems into phenotypic building blocks, which allows them to overlap while maximizing the number of times a building block is reused across several conditions. Different biological systems present building blocks whose reusability ranges from single use (e.g. condition specific) to constitutive, although their average reusability is not always higher than random equivalents of the system. These decompositions reveal a distinct distribution of building block sizes in real biological systems. This distribution stems, in part, from the peculiar usage pattern of the elements of biological systems, and constitutes a new angle to study the evolution of modularity.

Diversification of Secondary Metabolite Biosynthetic Gene Clusters Coincides with Lineage Divergence in Streptomyces

We have identified Streptomyces sister-taxa which share a recent common ancestor and nearly identical small subunit (SSU) rRNA gene sequences, but inhabit distinct geographic ranges demarcated by latitude and have sufficient genomic divergence to represent distinct species. Here, we explore the evolutionary dynamics of secondary metabolite biosynthetic gene clusters (SMGCs) following lineage divergence of these sister-taxa. These sister-taxa strains contained 310 distinct SMGCs belonging to 22 different gene cluster classes. While there was broad conservation of these 22 gene cluster classes among the genomes analyzed, each individual genome harbored a different number of gene clusters within each class. A total of nine SMGCs were conserved across nearly all strains, but the majority (57%) of SMGCs were strain-specific. We show that while each individual genome has a unique combination of SMGCs, this diversity displays lineage-level modularity. Overall, the northern-derived (NDR) clade had more SMGCs than the southern-derived (SDR) clade (40.7 ± 3.9 and 33.8 ± 3.9, mean and S.D., respectively). This difference in SMGC content corresponded with differences in the number of predicted open reading frames (ORFs) per genome (7775 ± 196 and 7093 ± 205, mean and S.D., respectively) such that the ratio of SMGC:ORF did not differ between sister-taxa genomes. We show that changes in SMGC diversity between the sister-taxa were driven primarily by gene acquisition and deletion events, and these changes were associated with an overall change in genome size which accompanied lineage divergence.