Abstract
The fundamental question of whether different microbial species will co-exist or compete in a given environment depends on context, composition and environmental constraints. Model microbial systems can yield some general principles related to this question. In this study we employed a naturally occurring co-culture composed of heterotrophic bacteria, Halomonas sp. HL-48 and Marinobacter sp. HL-58, to ask two fundamental scientific questions: 1) how do the phenotypes of two naturally co-existing species respond to partnership as compared to axenic growth? and 2) how do growth and molecular phenotypes of these species change with respect to competitive and commensal interactions? We hypothesized – and confirmed – that co-cultivation under glucose as the sole carbon source would result in competitive interactions. Similarly, when glucose was swapped with xylose, the interactions became commensal because Marinobacter HL-58 was supported by metabolites derived from Halomonas HL-48. Each species responded to partnership by changing both its growth and molecular phenotype as assayed via batch growth kinetics and global transcriptomics. These phenotypic responses depended on nutrient availability and so the environment ultimately controlled how they responded to each other. This simplified model community revealed that microbial interactions are context-specific and different environmental conditions dictate how interspecies partnerships will unfold.
Highlights
In microbial life, a cell’s phenotype is determined by the properties encoded in its genome and by its environment
Our co-cultivation experiments demonstrated that interspecies partnerships changed the growth phenotypes of Halomonas HL-48 and Marinobacter HL-58
Co-cultivation on glucose led to competition, in which growth of Halomonas HL-48 outpaced Marinobacter HL-58 (Fig. 1D)
Summary
A cell’s phenotype is determined by the properties encoded in its genome and by its environment. Encode genes that enable it to import and assimilate fermentation products from its co-culture partner: acetate (acetyl-CoA synthetase; acs), formate (FNT family formate-nitrate transporter and a formate-tetrahydrofolate ligase; CD01DRAFT_0289), and ethanol (PQQ-dependent ethanol dehydrogenase; queDH) These complementary metabolic potentials make this co-culture system well-suited for testing phenotypes associated with substrate competition and commensal metabolite exchange. Growth phenotypes are direct manifestations of molecular phenotypes To assess both the response mechanism and outcome of co-culture under different nutrient-controlled interaction states which spawned either competitive or commensal interactions, we measured the specific growth rates of each species and changes in transcript abundance and metabolite accumulation. Our results suggest that environment can change the nature of interspecies interactions, and that community context modulates an individual species’ response to the environment
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