Interrogation of the integrated mobile genetic elements in gut-associated Bacteroidaceae with a consensus prediction approach

ABSTRACTExploration of mobile genetic element (MGE) diversity and relatedness is vital to understanding microbial communities, especially the gut microbiome, where the mobilization of antibiotic resistance and pathogenicity genes has important clinical consequences. Current MGE prediction tools are biased toward elements similar to previously-identified MGEs, especially tailed phages of proteobacterial hosts. Further, there is a need for methods to examine relatedness and gene sharing among MGEs. We present VICSIN, a consensus approach for MGE prediction and clustering of predictions to provide classification. Testing of VICSIN on datasets of Pseudomonas aeruginosa and Bacteroides fragilis genomes suggests VICSIN is the optimal approach to predict integrated MGEs from poorly-explored host taxa, because of its increased sensitivity and accuracy. We applied VICSIN to a dataset of gut-associated Bacteroidaceae genomes, identifying 816 integrated MGEs falling into 95 clusters, most of which are novel. VICSIN’s fast and simple network-building scheme revealed a high degree of gene sharing within and between related MGE clusters. Shared gene functions across MGEs include core mobilization functions and accessory gene content, such as type VI secretion systems and antibiotic resistance genes. The MGEs identified here encode a large portion of unknown gene content, emphasizing the fact that the full diversity of MGEs and the factors they encode remain very poorly understood. Together, this work motivates more exploration of the gut mobilome, which is likely one of the most potent drivers of microbial evolution in the human microbiome.IMPORTANCEMobile genetic elements (MGEs), including phages and integrative and conjugative elements (ICEs), drive the diversity and function of microbial communities through horizontal gene transfer. Current tools to predict MGEs in genomic sequence data are highly focused on phages, and are biased against the discovery of novel MGEs. We present VICSIN, a consensus approach to MGE prediction that is able to find a diversity of MGEs, particularly in poorly-understood bacterial taxa. By applying VICSIN to a large database of diverse Bacteroidaceae genomes, we have been able to get a distinct view of the gut mobilome, extending beyond the phageome. These novel MGEs belong to related groups, sharing a significant amount of functional gene content within and between groups, supporting a mosaic model of evolution for ICEs. Understanding how phages evolve in Bacteroidaceae hosts, however, remains elusive and highlights the need for more experimental research.

Viruses of the Thermotogota; the vehicles on the highways of gene sharing

Viruses are drivers of microbial ecology and evolution controlling populations and disseminating DNA laterally among the cells they infect. Phylogenetic and comparative genomic analyses of Thermotogota bacteria have shown high levels of lateral gene transfer with distantly related organisms, particularly with Firmicutes. One likely source of such DNA transfers is viruses, however, to date only three temperate viruses infecting Marinitoga bacteria have been characterized in this phylum. Here we use a bioinformatic approach to identify an additional 17 proviruses integrated into genomes of eight Thermotogota genera including Marinitoga. We also induce viral particle production from one of the newly identified proviruses. The proviruses fall into two groups based on sequence similarities, gene synteny and virus classification tools. Group-1 shows similar genome structure to the three previously identified Marinitoga viruses while Group-2 are distantly related to these viruses and have different genome organization. Both groups show close connections to Firmicutes in genomic- and phylogenetic analyses, and the Group-2 viruses show evidence of very recent transfer between these lineages and are likely capable of infecting cells from both phyla. We suggest that viruses are responsible for a large portion of the laterally transferred DNA between these distantly related lineages.

Slightly beneficial genes are retained by bacteria evolving DNA uptake despite selfish elements

Horizontal gene transfer (HGT) and gene loss result in rapid changes in the gene content of bacteria. While HGT aids bacteria to adapt to new environments, it also carries risks such as selfish genetic elements (SGEs). Here, we use modelling to study how HGT of slightly beneficial genes impacts growth rates of bacterial populations, and if bacterial collectives can evolve to take up DNA despite selfish elements. We find four classes of slightly beneficial genes: indispensable, enrichable, rescuable, and unrescuable genes. Rescuable genes — genes with small fitness benefits that are lost from the population without HGT — can be collectively retained by a community that engages in costly HGT. While this ‘gene-sharing’ cannot evolve in well-mixed cultures, it does evolve in a spatial population like a biofilm. Despite enabling infection by harmful SGEs, the uptake of foreign DNA is evolutionarily maintained by the hosts, explaining the coexistence of bacteria and SGEs.

Plasmids Shape the Diverse Accessory Resistomes of Escherichia coli ST131

The human gut microbiome includes beneficial, commensal and pathogenic bacteria that possess antimicrobial resistance (AMR) genes and exchange these predominantly through conjugative plasmids. Escherichia coli is a significant component of the gastrointestinal microbiome and is typically non-pathogenic in this niche. In contrast, extra-intestinal pathogenic E. coli (ExPEC) including ST131 may occupy other environments like the urinary tract or bloodstream where they express genes enabling AMR and host adhesion like type 1 fimbriae. The extent to which non-pathogenic gut E. coli and infectious ST131 share AMR genes and key associated plasmids remains understudied at a genomic level. Here, we examined AMR gene sharing between gut E. coli and ST131 to discover an extensive shared preterm infant resistome. In addition, individual ST131 show extensive AMR gene diversity highlighting that analyses restricted to the core genome may be limiting and could miss AMR gene transfer patterns. We show that pEK499-like segments are ancestral to most ST131 Clade C isolates, contrasting with a minority with substantial pEK204-like regions encoding a type IV fimbriae operon. Moreover, ST131 possess extensive diversity at genes encoding type 1, type IV, P and F17-like fimbriae, particular within subclade C2. The type, structure and composition of AMR genes, plasmids and fimbriae varies widely in ST131 and this may mediate pathogenicity and infection outcomes.

M171. THE GENE-SHARING RELATIONSHIP OF SCHIZOPHRENIA WITH OTHER MENTAL OR SYSTEMIC DISORDERS: A DISEASE-SIMILARITY NETWORK ANALYSIS FOCUSED ON EGOCENTRIC NETWORK

Background Schizophrenia is an archetypal example that a psychiatric illness may not merely be a mental or a brain disorder but rather a systemic illness. It can be glimpsed from a wide range of biomarkers that span all the imaginable body systems, and from higher co-morbidity with other systemic illnesses. However, quantitative analysis of schizophrenia’s relationship with other diseases are not yet satisfactory. Genome-wide association studies have identified more than hundreds of genetic loci associated with schizophrenia. In turn, these loci are associated with a wide variety of other diseases. From this gene-disease relationship, a bipartite network can be built which, after appropriate projection, could help to map a complex disease-similarity network. In case of schizophrenia, it would reveal the position of schizophrenia among the broader categories of systemic illnesses. Methods DisGeNET is a discovery platform which contains one of the largest collections of gene-disease association data. The major source of the integrated data is the automatized curation from MEDLINE abstract. Therefore, it contains the timestamp of reported gene-disease association. Gene-disease-timestamp (year of publication) triplet was fed into a Neo4J graph database platform. From this, disease-disease relationships with shared gene count and Jaccard similarity score was extracted. The network structure of level 1.5 egocentric network centered upon schizophrenia was inspected. Louvain community detection algorithm was applied to expose underlying group structure among the 1st order alters. For comparison, similar ego-networks centered upon several major psychiatric illnesses were also inspected. Finally, the yearly variation of Jaccard score which reflected the accumulation of research data were monitored. Results The diseases which showed the highest Jaccard score (j) were bipolar disorder (j=0.203) and depressive disorder (j=0.190) as expected. Other diseases with meaningful similarity could be grouped into three communities: 1) psychiatric illness including bipolar/depressive disorder, 2) a variety of malignancies including neuroblastoma (j=0.083), stomach cancer (j=0.070) and pancreatic cancer (j=0.065) 3) other systemic illnesses including multiple sclerosis (j=0.088), metabolic syndrome (j=0.076), myocardial infarction (j=0.073), rheumatoid arthritis (j=0.070), lupus erythematosus (0.056). The gene-sharing relationship with systemic illnesses (malignancies and other) began to be revealed after 2005. Since then, more and more evidences were accumulated to solidify the schizophrenia’s link with systemic illnesses. Discussion Recently, a couple of large-scale epidemiological studies verified the significant correlation between prevalence of schizophrenia and cancer/autoimmune disorders. The present study results may augment these epidemiological data and thus strongly support the concept of schizophrenia as a systemic illness. Gene-sharing and its reflection in prevalence data would indicate deeper link at the level of pathogenesis with systemic illnesses. Recently, many authors contemplated the possible link between schizophrenia and cancer in terms of cell cycle regulation and control of apoptosis. Likewise, others suspected immunological disturbance as the fundamental mechanism of schizophrenia. In this vein, the need for extending the concept of mental disorders as a focused manifestation of systemic illness seems gaining impetus.

Slightly beneficial genes are retained by evolving Horizontal Gene Transfer despite selfish elements

Horizontal gene transfer (HGT) is a key component of bacterial evolution, which in concert with gene loss can result in rapid changes in gene content. While HGT can evidently aid bacteria to adapt to new environments, it also carries risks since bacteria may pick up selfish genetic elements (SGEs). Here, we use modeling to study how bacterial growth rates are affected by HGT of slightly beneficial genes, if bacteria can evolve HGT to improve their growth rates, and when HGT is evolutionarily maintained in light of harmful SGEs. We find that we can distinguish between four classes of slightly beneficial genes: indispensable, enrichable, rescuable, and unrescuable genes. Rescuable genes – genes that confer small fitness benefits and are lost from the population in the absence of HGT — can be collectively retained by a bacterial community that engages in HGT. While this ‘gene-sharing’ cannot evolve in well-mixed cultures, it does evolve in a spatially structured population such as a biofilm. Although HGT does indeed enable infection by harmful SGEs, HGT is nevertheless evolutionarily maintained by the hosts, explaining the stable coexistence and co-evolution of bacteria and SGEs.

Evolution of Yin and Yang isoforms of a chromatin remodeling subunit precedes the creation of two genes

Genes can encode multiple isoforms, broadening their functions and providing a molecular substrate to evolve phenotypic diversity. Evolution of isoform function is a potential route to adapt to new environments. Here we show that de novo, beneficial alleles in the nurf-1 gene became fixed in two laboratory lineages of C. elegans after isolation from the wild in 1951, before methods of cryopreservation were developed. nurf-1 encodes an ortholog of BPTF, a large (>300 kD) multidomain subunit of the NURF chromatin remodeling complex. Using CRISPR-Cas9 genome editing and transgenic rescue, we demonstrate that in C. elegans, nurf-1 has split into two, largely non-overlapping isoforms (NURF-1.D and NURF-1.B, which we call Yin and Yang, respectively) that share only two of 26 exons. Both isoforms are essential for normal gametogenesis but have opposite effects on male/female gamete differentiation. Reproduction in hermaphrodites, which involves production of both sperm and oocytes, requires a balance of these opposing Yin and Yang isoforms. Transgenic rescue and genetic position of the fixed mutations suggest that different isoforms are modified in each laboratory strain. In a related clade of Caenorhabditis nematodes, the shared exons have duplicated, resulting in the split of the Yin and Yang isoforms into separate genes, each containing approximately 200 amino acids of duplicated sequence that has undergone accelerated protein evolution following the duplication. Associated with this duplication event is the loss of two additional nurf-1 transcripts, including the long-form transcript and a newly identified, highly expressed transcript encoded by the duplicated exons. We propose these lost transcripts are non-functional side products necessary to transcribe the Yin and Yang transcripts in the same cells. Our work demonstrates how gene sharing, through the production of multiple isoforms, can precede the creation of new, independent genes.