Monasky, R. | Search bioRxiv

bioRxiv2021

Bile Acid Regulates the Colonization and Dissemination of Candida albicans from the Gastrointestinal Tract by Controlling Host Defense System and Microbiota

Candida albicans (CA), a commensal and opportunistic eukaryotic organism, frequently inhabits the gastrointestinal (GI) tract and causes life-threatening infections. Antibiotic-induced gut dysbiosis is a major risk factor for increased CA colonization and dissemination from the GI tract. We identified a significant increase of taurocholic acid (TCA), a major bile acid in antibiotic-treated mice susceptible to CA infection. In vivo findings indicate that administration of TCA through drinking water is sufficient to induce colonization and dissemination of CA in wild type and immunosuppressed mice. Treatment with TCA significantly reduced mRNA expression of immune genes ang4 and Cxcr3 in the colon. In addition, TCA significantly decreased the relative abundance of three culturable species of commensal bacteria, Turicibacter sanguinis, Lactobacillus johnsonii, and Clostridium celatum, in both cecal contents and mucosal scrapings from colon. Taken together, our results indicate that TCA promotes fungal colonization and dissemination of CA from the GI tract by controlling host defense system and intestinal microbiota that play a critical role in regulating CA in the intestine. ImportanceBroad-spectrum antibiotics, FDA-approved bile acid drugs, and probiotics used to control metabolic and infectious diseases profoundly alter the level of TCA in the gut. Furthermore, TCA level is highly altered in a subset of cancer, colitis and surgery patients who are highly susceptible to CA infection. Inadvertently, these therapies and disease conditions could be either promoting CA colonization and dissemination. Our findings indicate that TCA alone can induce fungal colonization and dissemination from the intestine. Results from this study will have a significant impact in understanding how bile acids interact with the microbiota and host in regulating invasive fungal infections that originate from the intestine and to develop potential new antifungal therapeutics.

microbiology↗

bioRxiv2019

Evolutionary Stalling in the Optimization of the Translation Machinery

Cells consist of molecular modules which perform vital biological functions. Cellular modules are key units of adaptive evolution because organismal fitness depends on their performance. Theory shows that in rapidly evolving populations, such as those of many microbes, adaptation is driven primarily by common beneficial mutations with large effects, while other mutations behave as if they are effectively neutral. As a consequence, if a module can be improved only by rare and/or weak beneficial mutations, its adaptive evolution would stall. However, such evolutionary stalling has not been empirically demonstrated, and it is unclear to what extent stalling may limit the power of natural selection to improve modules. Here, we empirically characterize how natural selection improves the translation machinery (TM), an essential cellular module. We experimentally evolved populations of Escherichia coli with genetically perturbed TMs for 1,000 generations. Populations with severe TM defects initially adapted via mutations in the TM, but TM adaptation stalled within about 300 generations. We estimate that the genetic load in our populations incurred by residual TM defects ranges from 0.5 to 19%. Finally, we found evidence that both epistasis and the depletion of the pool of beneficial mutations contributed to evolutionary stalling. Our results suggest that cellular modules may not be fully optimized by natural selection despite the availability of adaptive mutations.

evolutionary biology↗