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Initial symbiont contact orchestrates host-organ-wide transcriptional changes that prime tissue colonization.

ABSTRACT: Upon transit to colonization sites, bacteria often experience critical priming that prepares them for subsequent, specific interactions with the host; however, the underlying mechanisms are poorly described. During initiation of the symbiosis between the bacterium Vibrio fischeri and its squid host, which can be observed directly and in real time, approximately five V. fischeri cells aggregate along the mucociliary membranes of a superficial epithelium prior to entering host tissues. Here, we show that these few early host-associated symbionts specifically induce robust changes in host gene expression that are critical to subsequent colonization steps. This exquisitely sensitive response to the host's specific symbiotic partner includes the upregulation of a host endochitinase, whose activity hydrolyzes polymeric chitin in the mucus into chitobiose, thereby priming the symbiont and also producing a chemoattractant gradient that promotes V. fischeri migration into host tissues. Thus, the host responds transcriptionally upon initial symbiont contact, which facilitates subsequent colonization.

SUBMITTER: Kremer N

PROVIDER: S-EPMC3928804 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Initial symbiont contact orchestrates host-organ-wide transcriptional changes that prime tissue colonization.

Kremer Natacha N Philipp Eva E R EE Carpentier Marie-Christine MC Brennan Caitlin A CA Kraemer Lars L Altura Melissa A MA Augustin René R Häsler Robert R Heath-Heckman Elizabeth A C EA Peyer Suzanne M SM Schwartzman Julia J Rader Bethany A BA Ruby Edward G EG Rosenstiel Philip P McFall-Ngai Margaret J MJ

Cell host & microbe 20130801 2

Upon transit to colonization sites, bacteria often experience critical priming that prepares them for subsequent, specific interactions with the host; however, the underlying mechanisms are poorly described. During initiation of the symbiosis between the bacterium Vibrio fischeri and its squid host, which can be observed directly and in real time, approximately five V. fischeri cells aggregate along the mucociliary membranes of a superficial epithelium prior to entering host tissues. Here, we sh ...[more]

PMID: 23954157

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Project description:One of the most important events in an animal's life history is the initial colonization by its microbial symbionts, yet little is known about this event's immediate impacts on the extent of host gene expression or the molecular mechanisms controlling it. MicroRNAs (miRNAs) are short, noncoding RNAs that bind to target mRNAs, rapidly shaping gene expression by posttranscriptional control of mRNA translation and decay. Here, we show that, in the experimentally tractable binary squid-vibrio symbiosis, colonization of the light organ induces extensive changes in the miRNA transcriptome. Examination of the squid genome revealed the presence of evolutionarily conserved genes encoding elements essential for the production and processing of miRNAs. At 24 h postcolonization, 215 host miRNAs were detected in the light organ, 26 of which were differentially expressed in response to the symbionts. A functional enrichment analysis of genes potentially targeted by downregulation of certain miRNAs at the initiation of symbiosis revealed two major gene ontology (GO) term categories, neurodevelopment and tissue remodeling. This symbiont-induced downregulation is predicted to promote these activities in host tissues and is consistent with the well-described tissue remodeling that occurs at the onset of the association. Conversely, predicted targets of upregulated miRNAs, including the production of mucus, are consistent with attenuation of immune responses by symbiosis. Taken together, our data provide evidence that, at the onset of symbiosis, host miRNAs in the light organ drive alterations in gene expression that (i) orchestrate the symbiont-induced development of host tissues, and (ii) facilitate the partnership by dampening the immune response.IMPORTANCE Animals often acquire their microbiome from the environment at each generation, making the initial interaction of the partners a critical event in the establishment and development of a stable, healthy symbiosis. However, the molecular nature of these earliest interactions is generally difficult to study and poorly understood. We report that, during the initial 24 h of the squid-vibrio association, a differential expression of host miRNAs is triggered by the presence of the microbial partner. Predicted mRNA targets of these miRNAs were associated with regulatory networks that drive tissue remodeling and immune suppression, two major symbiosis-induced developmental outcomes in this and many other associations. These results implicate regulation by miRNAs as key to orchestrating the critical transcriptional responses that occur very early during the establishment of a symbiosis. Animals with more complex microbiota may have similar miRNA-driven responses as their association is initiated, supporting an evolutionary conservation of symbiosis-induced developmental mechanisms.

Project description:UnlabelledAnimal development and physiology depend on beneficial interactions with microbial symbionts. In many cases, the microbial symbionts are horizontally transmitted among hosts, thereby making the acquisition of these microbes from the environment an important event within the life history of each host. The light organ symbiosis established between the Hawaiian squid Euprymna scolopes and the bioluminescent bacterium Vibrio fischeri is a model system for examining how hosts acquire horizontally transmitted microbial symbionts. Recent studies have revealed that the light organ of wild-caught E. scolopes squid contains polyclonal populations of V. fischeri bacteria; however, the function and development of such strain diversity in the symbiosis are unknown. Here, we report our phenotypic and phylogenetic characterizations of FQ-A001, which is a V. fischeri strain isolated directly from the light organ of an E. scolopes individual. Relative to the type strain ES114, FQ-A001 exhibits similar growth in rich medium but displays increased bioluminescence and decreased motility in soft agar. FQ-A001 outcompetes ES114 in colonizing the crypt spaces of the light organs. Remarkably, we find that animals cocolonized with FQ-A001 and ES114 harbor singly colonized crypts, in contrast to the cocolonized crypts observed from competition experiments involving single genotypes. The results with our two-strain system suggest that strain diversity within the squid light organ is a consequence of diversity in the single-strain colonization of individual crypt spaces.ImportanceThe developmental programs and overall physiologies of most animals depend on diverse microbial symbionts that are acquired from the environment. However, the basic principles underlying how microbes colonize their hosts remain poorly understood. Here, we report our findings of bacterial strain competition within the coevolved animal-microbe symbiosis composed of the Hawaiian squid and bioluminescent bacterium Vibrio fischeri Using fluorescent proteins to differentially label two distinct V. fischeri strains, we find that the strains are unable to coexist in the same niche within the host. Our results suggest that strain competition for distinct colonization sites dictates the strain diversity associated with the host. Our study provides a platform for studying how strain diversity develops within a host.

Project description:Staphylococcus aureus is a significant cause of infections worldwide and is able to utilize aerobic respiration, anaerobic respiration, or fermentation as the means by which it generates the energy needed for proliferation. Aerobic respiration is supported by heme-dependent terminal oxidases that catalyze the final step of aerobic respiration, the reduction of O2 to H2O. An inability to respire forces bacteria to generate energy via fermentation, resulting in reduced growth. Elucidating the roles of these energy-generating pathways during colonization of the host could uncover attractive therapeutic targets. Consistent with this idea, we report that inhibiting aerobic respiration by inactivating heme biosynthesis significantly impairs the ability of S. aureus to colonize the host. Two heme-dependent terminal oxidases support aerobic respiration of S. aureus, implying that the staphylococcal respiratory chain is branched. Systemic infection with S. aureus mutants limited to a single terminal oxidase results in an organ-specific colonization defect, resulting in reduced bacterial burdens in either the liver or the heart. Finally, inhibition of aerobic respiration can be achieved by exposing S. aureus to noniron heme analogues. These data provide evidence that aerobic respiration plays a major role in S. aureus colonization of the host and that this energy-generating process is a viable therapeutic target. Staphylococcus aureus poses a significant threat to public health as antibiotic-resistant isolates of this pathogen continue to emerge. Our understanding of the energy-generating processes that allow S. aureus to proliferate within the host is incomplete. Host-derived heme is the preferred source of nutrient iron during infection; however, S. aureus can synthesize heme de novo and use it to facilitate aerobic respiration. We demonstrate that S. aureus heme biosynthesis powers a branched aerobic respiratory chain composed of two terminal oxidases. The importance of having two terminal oxidases is demonstrated by the finding that each plays an essential role in colonizing distinct organs during systemic infection. Additionally, this process can be targeted by small-molecule heme analogues called noniron protoporphyrins. This study serves to demonstrate that heme biosynthesis supports two terminal oxidases that are required for aerobic respiration and are also essential for S. aureus pathogenesis.

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Initial symbiont contact orchestrates host-organ-wide transcriptional changes that prime tissue colonization.

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Initial symbiont contact orchestrates host-organ-wide transcriptional changes that prime tissue colonization.

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