Lactobacillus bile salt hydrolase substrate specificity governs bacterial fitness and host colonization
The gut microbiome has a significant impact on human metabolism and health. Bile acids have already been shown to influence gut colonization substantially. This bile acid pool is steadily modified by microbial bile salt hydrolases (BSHs), though the utility of BSH expression for bacteria has not been elucidated.
In this study, Dr. Foley and colleagues of the North Carolina State University examined the impact of BSH expression on probiotic lactobacilli colonization, both in vivo and in vitro, using Lactobacillus acidophilus and Lactobacillus gasseri.
The results revealed a high complexity of interactions between BSHs of different strains and various conjugated bile acids. This interplay determined the toxicity of conjugated bile acids against Lactobacillus, based on changing levels of modified bile acids. Interestingly, these results disprove previous assumptions that BSHs detoxify bile acids through deconjugation, and instead show that toxicity during Lactobacillus growth is determined by the enzymatic characteristics of BSHs and intrinsic features of bile acids.
Furthermore, substrate specificity differed between BSH type and bacterial strains. This means that while BSH expression does not provide a universal advantage for bacterial fitness, BSHs can influence bacterial selection. BSH activity seems to drive bacterial competition depending on bile acid pool and environment.
These results suggest that variable levels of bile acids with different types of conjugations are potent modulators of the gut microbiota. Therefore, both bile acids and BSHs may be potential targets for therapeutic or dietary interventions to improve human health.
Foley MH, O’Flaherty S, Allen G, Rivera AJ, Stewart AK, Barrangou R et al.: Lactobacillus bile salt hydrolase substrate specificity governs bacterial fitness and host colonization. (2021) PNAS | https://doi.org/10.1073/pnas.2017709118