Diversification of Type VI Secretion System Toxins Reveals Ancient Antagonism among Bee Gut Microbes

ABSTRACT Microbial communities are shaped by interactions among their constituent members. Some Gram-negative bacteria employ type VI secretion systems (T6SSs) to inject protein toxins into neighboring cells. These interactions have been theorized to affect the composition of host-associated microbiomes, but the role of T6SSs in the evolution of gut communities is not well understood. We report the discovery of two T6SSs and numerous T6SS-associated Rhs toxins within the gut bacteria of honey bees and bumble bees. We sequenced the genomes of 28 strains of Snodgrassella alvi, a characteristic bee gut microbe, and found tremendous variability in their Rhs toxin complements: altogether, these strains appear to encode hundreds of unique toxins. Some toxins are shared with Gilliamella apicola, a coresident gut symbiont, implicating horizontal gene transfer as a source of toxin diversity in the bee gut. We use data from a transposon mutagenesis screen to identify toxins with antibacterial function in the bee gut and validate the function and specificity of a subset of these toxin and immunity genes in Escherichia coli. Using transcriptome sequencing, we demonstrate that S. alvi T6SSs and associated toxins are upregulated in the gut environment. We find that S. alvi Rhs loci have a conserved architecture, consistent with the C-terminal displacement model of toxin diversification, with Rhs toxins, toxin fragments, and cognate immunity genes that are expressed and confer strong fitness effects in vivo. Our findings of T6SS activity and Rhs toxin diversity suggest that T6SS-mediated competition may be an important driver of coevolution within the bee gut microbiota. IMPORTANCE The structure and composition of host-associated bacterial communities are of broad interest, because these communities affect host health. Bees have a simple, conserved gut microbiota, which provides an opportunity to explore interactions between species that have coevolved within their host over millions of years. This study examined the role of type VI secretion systems (T6SSs)—protein complexes used to deliver toxic proteins into bacterial competitors—within the bee gut microbiota. We identified two T6SSs and diverse T6SS-associated toxins in bacterial strains from bees. Expression of these genes is increased in bacteria in the bee gut, and toxin and immunity genes demonstrate antibacterial and protective functions, respectively, when expressed in Escherichia coli. Our results suggest that coevolution among bacterial species in the bee gut has favored toxin diversification and maintenance of T6SS machinery, and demonstrate the importance of antagonistic interactions within host-associated microbial communities. IMPORTANCE The structure and composition of host-associated bacterial communities are of broad interest, because these communities affect host health. Bees have a simple, conserved gut microbiota, which provides an opportunity to explore interactions between species that have coevolved within their host over millions of years. This study examined the role of type VI secretion systems (T6SSs)—protein complexes used to deliver toxic proteins into bacterial competitors—within the bee gut microbiota. We identified two T6SSs and diverse T6SS-associated toxins in bacterial strains from bees. Expression of these genes is increased in bacteria in the bee gut, and toxin and immunity genes demonstrate antibacterial and protective functions, respectively, when expressed in Escherichia coli. Our results suggest that coevolution among bacterial species in the bee gut has favored toxin diversification and maintenance of T6SS machinery, and demonstrate the importance of antagonistic interactions within host-associated microbial communities.

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Evolution of Interbacterial Antagonism in Bee Gut Microbiota Reflects Host and Symbiont Diversification

mSystems ◽

10.1128/msystems.00063-21 ◽

2021 ◽

Vol 6 (3) ◽

Author(s):

Margaret I. Steele ◽

Nancy A. Moran

Keyword(s):

Gut Microbiota ◽

Protein Complexes ◽

Bacterial Species ◽

Structural Components ◽

Secretion Systems ◽

Gram Negative ◽

Content Type ◽

Social Bees ◽

Type Vi Secretion ◽

Bacterial Lineages

ABSTRACT Gram-negative bacteria frequently possess type VI secretion systems (T6SSs), protein complexes that are able to inject toxic proteins into nearby cells. Many aspects of T6SS structure and function have been characterized for model species, but less is known about the evolutionary processes that shape T6SS and effector (toxin) diversity in host-associated microbial communities. The bee gut microbiota is a simple community that has codiversified with bees for >80 million years. This study investigated how complements of T6SSs and effectors within the bee microbiota changed as bacteria and their hosts diversified into isolated species. We used protein homology to survey 198 isolate genomes of 9 Gram-negative species for genes encoding T6SS structural components; Rhs toxins, which are common T6SS effectors; and VgrG proteins, which are structural components associated with specific toxins. T6SS loci were present in 5 species clusters found only in bees, namely Apibacter spp., Gilliamella spp., Frischella perrara, “Candidatus Schmidhempelia bombi,” and Snodgrassella alvi. The distribution of T6SS loci suggests that at least 3 were present in the microbiota of the common ancestor of social bees and that loss of these genes in some bacterial lineages was linked to both host and bacterial speciation. Isolates differed enormously in repertoires of Rhs and VgrG proteins. We found that bacterial species employ different mechanisms for toxin acquisition and diversification and that species and strains sometimes lose the T6SS entirely, likely causing shifts in competitive dynamics within these communities. IMPORTANCE Antagonistic interactions between bacteria affect diversity and dynamics of host-associated communities, including gut communities that are linked to host health. In many bacterial communities, including human and honey bee gut microbiotas, antagonism is mediated by type VI secretion systems (T6SSs) that deliver lethal toxins to competing strains. In this study, we explored how T6SSs and associated toxins have evolved in the simple, host-specific gut microbiota of honey bees and bumble bees. Using comparative genomics, we explored the conservation, recombination, horizontal transfer, and loss of T6SSs and effectors during 80 million years of evolution of this bee-associated community. We find that that patterns of T6SS loss and retention are linked to differences in biology across host species, while trends in effector diversification are mostly specific to bacterial lineages.

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10 THE ROLE OF DIETARY L-SERINE IN THE REGULATION OF INTESTINAL MUCUS BARRIER DURING INFLAMMATION

Inflammatory Bowel Diseases ◽

10.1093/ibd/zaa010.110 ◽

2020 ◽

Vol 26 (Supplement_1) ◽

pp. S42-S42

Author(s):

Kohei Sugihara ◽

Nobuhiko Kamada

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Gut Microbiota ◽

Control Diet ◽

Bacterial Strains ◽

Germ Free ◽

Intestinal Mucus ◽

Gnotobiotic Mice ◽

Mucus Barrier

Abstract Background Recent accumulating evidence suggests that amino acids have crucial roles in the maintenance of intestinal homeostasis. In inflammatory bowel disease (IBD), amino acid metabolism is changed in both host and the gut microbiota. Among amino acids, L-serine plays a central role in several metabolic processes that are essential for the growth and survival of both mammalian and bacterial cells. However, the role of L-serine in intestinal homeostasis and IBD remains incompletely understood. In this study, we investigated the effect of dietary L-serine on intestinal inflammation in a murine model of colitis. Methods Specific pathogen-free (SPF) mice were fed either a control diet (amino acid-based diet) or an L-serine-deficient diet (SDD). Colitis was induced by the treatment of dextran sodium sulfate (DSS). The gut microbiome was analyzed by 16S rRNA sequencing. We also evaluate the effect of dietary L-serine in germ-free mice and gnotobiotic mice that were colonized by a consortium of non-mucolytic bacterial strains or the consortium plus mucolytic bacterial strains. Results We found that the SDD exacerbated experimental colitis in SPF mice. However, the severity of colitis in SDD-fed mice was comparable to control diet-fed mice in germ-free condition, suggesting that the gut microbiota is required for exacerbation of colitis caused by the restriction of dietary L-serine. The gut microbiome analysis revealed that dietary L-serine restriction fosters the blooms of a mucus-degrading bacterium Akkermansia muciniphila and adherent-invasive Escherichia coli in the inflamed gut. Consistent with the expansion of mucolytic bacteria, SDD-fed mice showed a loss of the intestinal mucus layer. Dysfunction of the mucus barrier resulted in increased intestinal permeability, thereby leading to bacterial translocation to the intestinal mucosa, which subsequently increased the severity of colitis. The increased intestinal permeability and subsequent bacterial translocation were observed in SDD-fed gnotobiotic mice that colonized by mucolytic bacteria. In contrast, dietary L-serine restriction did not alter intestinal barrier integrity in gnotobiotic mice that colonized only by non-mucolytic bacteria. Conclusion Our results suggest that dietary L-serine regulates the integrity of the intestinal mucus barrier during inflammation by limiting the expansion of mucus degrading bacteria.

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Influence of pig farming on human Gut Microbiota: role of airborne microbial communities

Gut Microbes ◽

10.1080/19490976.2021.1927634 ◽

2021 ◽

Vol 13 (1) ◽

pp. 1-13

Author(s):

Julia Moor ◽

Tsering Wüthrich ◽

Suzanne Aebi ◽

Nadezda Mostacci ◽

Gudrun Overesch ◽

...

Keyword(s):

Gut Microbiota ◽

Microbial Communities ◽

Human Gut ◽

Human Gut Microbiota ◽

Pig Farming

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Discovery of novel community-relevant small proteins in a simplified human intestinal microbiome

Microbiome ◽

10.1186/s40168-020-00981-z ◽

2021 ◽

Vol 9 (1) ◽

Author(s):

Hannes Petruschke ◽

Christian Schori ◽

Sebastian Canzler ◽

Sarah Riesbeck ◽

Anja Poehlein ◽

...

Keyword(s):

Microbial Communities ◽

Intestinal Microbiota ◽

De Novo ◽

Bacterial Species ◽

Intestinal Microbiome ◽

Single Strain ◽

Small Proteins ◽

Human Intestinal Microbiota ◽

Wide Range

Abstract Background The intestinal microbiota plays a crucial role in protecting the host from pathogenic microbes, modulating immunity and regulating metabolic processes. We studied the simplified human intestinal microbiota (SIHUMIx) consisting of eight bacterial species with a particular focus on the discovery of novel small proteins with less than 100 amino acids (= sProteins), some of which may contribute to shape the simplified human intestinal microbiota. Although sProteins carry out a wide range of important functions, they are still often missed in genome annotations, and little is known about their structure and function in individual microbes and especially in microbial communities. Results We created a multi-species integrated proteogenomics search database (iPtgxDB) to enable a comprehensive identification of novel sProteins. Six of the eight SIHUMIx species, for which no complete genomes were available, were sequenced and de novo assembled. Several proteomics approaches including two earlier optimized sProtein enrichment strategies were applied to specifically increase the chances for novel sProtein discovery. The search of tandem mass spectrometry (MS/MS) data against the multi-species iPtgxDB enabled the identification of 31 novel sProteins, of which the expression of 30 was supported by metatranscriptomics data. Using synthetic peptides, we were able to validate the expression of 25 novel sProteins. The comparison of sProtein expression in each single strain versus a multi-species community cultivation showed that six of these sProteins were only identified in the SIHUMIx community indicating a potentially important role of sProteins in the organization of microbial communities. Two of these novel sProteins have a potential antimicrobial function. Metabolic modelling revealed that a third sProtein is located in a genomic region encoding several enzymes relevant for the community metabolism within SIHUMIx. Conclusions We outline an integrated experimental and bioinformatics workflow for the discovery of novel sProteins in a simplified intestinal model system that can be generically applied to other microbial communities. The further analysis of novel sProteins uniquely expressed in the SIHUMIx multi-species community is expected to enable new insights into the role of sProteins on the functionality of bacterial communities such as those of the human intestinal tract.

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Gut Microbiota and Acute Diverticulitis: Role of Probiotics in Management of This Delicate Pathophysiological Balance

Journal of Personalized Medicine ◽

10.3390/jpm11040298 ◽

2021 ◽

Vol 11 (4) ◽

pp. 298

Author(s):

Andrea Piccioni ◽

Laura Franza ◽

Mattia Brigida ◽

Christian Zanza ◽

Enrico Torelli ◽

...

Keyword(s):

Gut Microbiota ◽

Diverticular Disease ◽

Acute Diverticulitis ◽

Bacterial Species ◽

Mucosal Inflammation ◽

Abdominal Symptoms ◽

Pubmed Database ◽

Anti Inflammatory ◽

Key Terms

How can the knowledge of probiotics and their mechanisms of action be translated into clinical practice when treating patients with diverticular disease and acute diverticulitis? Changes in microbiota composition have been observed in patients who were developing acute diverticulitis, with a reduction of taxa with anti-inflammatory activity, such as Clostridium cluster IV, Lactobacilli and Bacteroides. Recent observations supported that a dysbiosis characterised by decreased presence of anti-inflammatory bacterial species might be linked to mucosal inflammation, and a vicious cycle results from a mucosal inflammation driving dysbiosis at the same time. An alteration in gut microbiota can lead to an altered activation of nerve fibres, and subsequent neuronal and muscular dysfunction, thus favoring abdominal symptoms’ development. The possible role of dysbiosis and mucosal inflammation in leading to dysmotility is linked, in turn, to bacterial translocation from the lumen of the diverticulum to perivisceral area. There, a possible activation of Toll-like receptors has been described, with a subsequent inflammatory reaction at the level of the perivisceral tissues. Being aware that bacterial colonisation of diverticula is involved in the pathogenesis of acute diverticulitis, the rationale for the potential role of probiotics in the treatment of this disease becomes clearer. For this review, articles were identified using the electronic PubMed database through a comprehensive search conducted by combining key terms such as “gut microbiota”, “probiotics and gut disease”, “probiotics and acute diverticulitis”, “probiotics and diverticular disease”, “probiotics mechanism of action”. However, the amount of data present on this matter is not sufficient to draw robust conclusions on the efficacy of probiotics for symptoms’ management in diverticular disease.

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Nanopore-Sequencing Characterization of the Gut Microbiota of Melolontha melolontha Larvae: Contribution to Protection against Entomopathogenic Nematodes?

Pathogens ◽

10.3390/pathogens10040396 ◽

2021 ◽

Vol 10 (4) ◽

pp. 396

Author(s):

Ewa Sajnaga ◽

Marcin Skowronek ◽

Agnieszka Kalwasińska ◽

Waldemar Kazimierczak ◽

Karolina Ferenc ◽

...

Keyword(s):

Gut Microbiota ◽

Entomopathogenic Nematodes ◽

Bacterial Species ◽

Antagonistic Activity ◽

Rrna Gene ◽

Nanopore Sequencing ◽

Bacterial Phyla ◽

Melolontha Melolontha

This study focused on the potential relationships between midgut microbiota of the common cockchafer Melolontha melolontha larvae and their resistance to entomopathogenic nematodes (EPN) infection. We investigated the bacterial community associated with control and unsusceptible EPN-exposed insects through nanopore sequencing of the 16S rRNA gene. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant bacterial phyla within the complex and variable midgut microbiota of the wild M. melolontha larvae. The core microbiota was found to include 82 genera, which accounted for 3.4% of the total number of identified genera. The EPN-resistant larvae differed significantly from the control ones in the abundance of many genera belonging to the Actinomycetales, Rhizobiales, and Clostridiales orders. Additionally, the analysis of the microbiome networks revealed different sets of keystone midgut bacterial genera between these two groups of insects, indicating differences in the mutual interactions between bacteria. Finally, we detected Xenorhabdus and Photorhabdus as gut residents and various bacterial species exhibiting antagonistic activity against these entomopathogens. This study paves the way to further research aimed at unravelling the role of the host gut microbiota on the output of EPN infection, which may contribute to enhancement of the efficiency of nematodes used in eco-friendly pest management.

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New Players in the Toxin Field: Polymorphic Toxin Systems in Bacteria

mBio ◽

10.1128/mbio.00285-15 ◽

2015 ◽

Vol 6 (3) ◽

Cited By ~ 73

Author(s):

Anne Jamet ◽

Xavier Nassif

Keyword(s):

In Silico ◽

Bacterial Strains ◽

Secretion Systems ◽

Toxic Activity ◽

New Family ◽

Small Proteins ◽

Immunity Genes ◽

Dependent Growth ◽

Contact Dependent Growth Inhibition ◽

Terminal Domains

ABSTRACTBacteria have evolved numerous strategies to increase their competitiveness and fight against each other. Indeed, a large arsenal of antibacterial weapons is available in order to inhibit the proliferation of competitor cells. Polymorphic toxin systems (PTS), recently identified by bioinformatics in all major bacterial lineages, correspond to such a system primarily involved in conflict between related bacterial strains. They are typically composed of a secreted multidomain toxin, a protective immunity protein, and multiple cassettes encoding alternative toxic domains. The C-terminal domains of polymorphic toxins carry the toxic activity, whereas the N-terminal domains are related to the trafficking mode.In silicoanalysis of PTS identified over 150 distinct toxin domains, including putative nuclease, deaminase, or peptidase domains. Immunity genes found immediately downstream of the toxin genes encode small proteins that protect bacteria against their own toxins or against toxins secreted by neighboring cells. PTS encompass well-known colicins and pyocins, contact-dependent growth inhibition systems which include CdiA and Rhs toxins and some effectors of type VI secretion systems. We have recently characterized the MafB toxins, a new family of PTS deployed by pathogenicNeisseriaspp. Many other putative PTS have been identified byin silicopredictions but have yet to be characterized experimentally. However, the high number of these systems suggests that PTS have a fundamental role in bacterial biology that is likely to extend beyond interbacterial competition.

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Identification of gut microbiome markers for schizophrenia delineates a potential role of Streptococcus

10.1101/774265 ◽

2019 ◽

Cited By ~ 1

Author(s):

Feng Zhu ◽

Yanmei Ju ◽

Wei Wang ◽

Qi Wang ◽

Ruijin Guo ◽

...

Keyword(s):

Gut Microbiota ◽

Validation Cohort ◽

Bacterial Species ◽

Metagenomic Sequencing ◽

Operating Characteristics ◽

Discovery Cohort ◽

Peripheral Tissues ◽

Functional Changes ◽

Microbial Biomarkers

AbstractEmerging evidence has linked the gut microbiota to schizophrenia. However, the functional changes in the gut microbiota and the biological role of individual bacterial species in schizophrenia have not been explored systematically. Here, we characterized the gut microbiota in schizophrenia using shotgun metagenomic sequencing of feces from a discovery cohort of 90 drug-free patients and 81 controls, as well as a validation cohort of 45 patients taking antipsychotics and 45 controls. We screened 83 schizophrenia-associated bacterial species and constructed a classifier comprising 26 microbial biomarkers that distinguished patients from controls with a 0.896 area under the receiver operating characteristics curve (AUC) in the discovery cohort and 0.765 AUC in the validation cohort. Our analysis of fecal metagenomes revealed that schizophrenia-associated gut–brain modules included short-chain fatty acids synthesis, tryptophan metabolism, and synthesis/degradation of neurotransmitters including glutamate, γ-aminobutyric acid, and nitric oxide. The schizophrenia-enriched gut bacterial species include several oral cavity-resident microbes, such as Streptococcus vestibularis. We transplanted Streptococcus vestibularis into the gut of the mice with antibiotic-induced microbiota depletion to explore its functional role. We observed that this microbe transiently inhabited the mouse gut and this was followed by hyperactivity and deficit in social behaviors, accompanied with altered neurotransmitter levels in peripheral tissues. In conclusion, our study identified 26 schizophrenia-associated bacterial species representing potential microbial targets for future treatment, as well as gut–brain modules, some of which may give rise to new microbial metabolites involved in the development of schizophrenia.

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T4SP Database 2.0: An Improved Database for Type IV Secretion Systems in Bacterial Genomes with New Online Analysis Tools

Computational and Mathematical Methods in Medicine ◽

10.1155/2016/9415459 ◽

2016 ◽

Vol 2016 ◽

pp. 1-4 ◽

Cited By ~ 3

Author(s):

Na Han ◽

Weiwen Yu ◽

Yujun Qiang ◽

Wen Zhang

Keyword(s):

Recipient Cell ◽

Bacterial Species ◽

Genetic Material ◽

Type Iv Secretion ◽

Bacterial Strains ◽

Secretion Systems ◽

Bacterial Genomes ◽

Type Iv ◽

Type Iv Secretion Systems ◽

User Friendly

Type IV secretion system (T4SS) can mediate the passage of macromolecules across cellular membranes and is essential for virulent and genetic material exchange among bacterial species. The Type IV Secretion Project 2.0 (T4SP 2.0) database is an improved and extended version of the platform released in 2013 aimed at assisting with the detection of Type IV secretion systems (T4SS) in bacterial genomes. This advanced version provides users with web server tools for detecting the existence and variations of T4SS genes online. The new interface for the genome browser provides a user-friendly access to the most complete and accurate resource of T4SS gene information (e.g., gene number, name, type, position, sequence, related articles, and quick links to other webs). Currently, this online database includes T4SS information of 5239 bacterial strains.Conclusions. T4SS is one of the most versatile secretion systems necessary for the virulence and survival of bacteria and the secretion of protein and/or DNA substrates from a donor to a recipient cell. This database on virB/D genes of the T4SS system will help scientists worldwide to improve their knowledge on secretion systems and also identify potential pathogenic mechanisms of various microbial species.

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Dissection of the Role of Pili and Type 2 and 3 Secretion Systems in Adherence and Biofilm Formation of an Atypical Enteropathogenic Escherichia coli Strain

Infection and Immunity ◽

10.1128/iai.00620-13 ◽

2013 ◽

Vol 81 (10) ◽

pp. 3793-3802 ◽

Cited By ~ 25

Author(s):

Rodrigo T. Hernandes ◽

Miguel A. De la Cruz ◽

Denise Yamamoto ◽

Jorge A. Girón ◽

Tânia A. T. Gomes

Keyword(s):

Escherichia Coli ◽

Biofilm Formation ◽

Coli Strain ◽

Mass Spectrometry Analysis ◽

Secretion Systems ◽

Content Type ◽

Spectrometry Analysis ◽

Rigid Rod

ABSTRACTAtypical enteropathogenicEscherichia coli(aEPEC) strains are diarrheal pathogens that lack bundle-forming pilus production but possess the virulence-associated locus of enterocyte effacement. aEPEC strain 1551-2 produces localized adherence (LA) on HeLa cells; however, its isogenic intimin (eae) mutant produces a diffuse-adherence (DA) pattern. In this study, we aimed to identify the DA-associated adhesin of the 1551-2eaemutant. Electron microscopy of 1551-2 identified rigid rod-like pili composed of an 18-kDa protein, which was identified as the major pilin subunit of type 1 pilus (T1P) by mass spectrometry analysis. Deletion offimAin 1551-2 affected biofilm formation but had no effect on adherence properties. Analysis of secreted proteins in supernatants of this strain identified a 150-kDa protein corresponding to SslE, a type 2 secreted protein that was recently reported to be involved in biofilm formation of rabbit and human EPEC strains. However, neither adherence nor biofilm formation was affected in a 1551-2sslEmutant. We then investigated the role of the EspA filament associated with the type 3 secretion system (T3SS) in DA by generating a doubleeae espAmutant. This strain was no longer adherent, strongly suggesting that the T3SS translocon is the DA adhesin. In agreement with these results, specific anti-EspA antibodies blocked adherence of the 1551-2eaemutant. Our data support a role for intimin in LA, for the T3SS translocon in DA, and for T1P in biofilm formation, all of which may act in concert to facilitate host intestinal colonization by aEPEC strains.

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