McMillan Arthur S, Foley Matthew H, Perkins Caroline E, Theriot Casey M
Genetics Program, Department of Biological Sciences, College of Science.
Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, United States of America.
bioRxiv. 2023 Jun 27:2023.06.27.546749. doi: 10.1101/2023.06.27.546749.
() is a Gram-negative gut bacterium that encodes enzymes that alter the bile acid pool in the gut. Primary bile acids are synthesized by the host liver and are modified by gut bacteria. encodes two bile salt hydrolases (BSHs), as well as a hydroxysteroid dehydrogenase (HSDH). We hypothesize that modifies the bile acid pool in the gut to provide a fitness advantage for itself. To investigate each gene's role, different combinations of genes encoding bile acid altering enzymes (, and ) were knocked out by allelic exchange, including a triple KO. Bacterial growth and membrane integrity assays were done in the presence and absence of bile acids. To explore if response to nutrient limitation changes due to the presence of bile acid altering enzymes, RNASeq analysis of WT and triple KO strains in the presence and absence of bile acids was done. WT is more sensitive to deconjugated bile acids (CA, CDCA, and DCA) compared to the triple KO, which also decreased membrane integrity. The presence of is detrimental to growth in conjugated forms of CDCA and DCA. RNA-Seq analysis also showed bile acid exposure impacts multiple metabolic pathways in , but DCA significantly increases expression of many genes in carbohydrate metabolism, specifically those in polysaccharide utilization loci or PULs, in nutrient limited conditions. This study suggests that bile acids encounters in the gut may signal the bacteria to increase or decrease its utilization of carbohydrates. Further study looking at the interactions between bacteria, bile acids, and the host may inform rationally designed probiotics and diets to ameliorate inflammation and disease.
Recent work on BSHs in Gram-negative bacteria, such as , has primarily focused on how they can impact host physiology. However, the benefits bile acid metabolism confers to the bacterium that performs it is not well understood. In this study we set out to define if and how uses its BSHs and HSDH to modify bile acids to provide a fitness advantage for itself and . Genes encoding bile acid altering enzymes were able to impact how responds to nutrient limitation in the presence of bile acids, specifically carbohydrate metabolism, affecting many polysaccharide utilization loci (PULs). This suggests that may be able to shift its metabolism, specifically its ability to target different complex glycans including host mucin, when it comes into contact with specific bile acids in the gut. This work will aid in our understanding of how to rationally manipulate the bile acid pool and the microbiota to exploit carbohydrate metabolism in the context of inflammation and other GI diseases.
（）是一种革兰氏阴性肠道细菌，它编码可改变肠道胆汁酸池的酶。初级胆汁酸由宿主肝脏合成，并由肠道细菌进行修饰。（该细菌）编码两种胆汁盐水解酶（BSH）以及一种羟基类固醇脱氢酶（HSDH）。我们推测（该细菌）会修饰肠道中的胆汁酸池，以给自己提供适应性优势。为了研究每个基因的作用，通过等位基因交换敲除了编码胆汁酸改变酶（、和）的不同基因组合，包括三基因敲除。在有和没有胆汁酸的情况下进行细菌生长和膜完整性测定。为了探究由于存在胆汁酸改变酶，（该细菌）对营养限制的反应是否发生变化，对野生型和三基因敲除菌株在有和没有胆汁酸的情况下进行了RNA测序分析。与三基因敲除菌株相比，野生型（该细菌）对去结合胆汁酸（CA、CDCA和DCA）更敏感，三基因敲除菌株的膜完整性也有所降低。（该细菌）的存在对CDCA和DCA结合形式的生长不利。RNA测序分析还表明，胆汁酸暴露会影响（该细菌）的多种代谢途径，但在营养受限条件下，DCA会显著增加碳水化合物代谢中许多基因的表达，特别是多糖利用位点（PUL）中的那些基因。这项研究表明，（该细菌）在肠道中遇到的胆汁酸可能会向细菌发出信号，使其增加或减少对碳水化合物的利用。进一步研究细菌、胆汁酸和宿主之间的相互作用，可能有助于合理设计益生菌和饮食，以改善炎症和疾病。
最近关于革兰氏阴性细菌（如该细菌）中胆汁盐水解酶的研究主要集中在它们如何影响宿主生理。然而，胆汁酸代谢赋予进行该代谢的细菌的益处尚未得到充分理解。在本研究中，我们着手确定（该细菌）是否以及如何利用其胆汁盐水解酶和羟基类固醇脱氢酶来修饰胆汁酸，以给自己和（另一细菌）提供适应性优势。编码胆汁酸改变酶的基因能够影响（该细菌）在有胆汁酸存在时对营养限制的反应，特别是碳水化合物代谢，影响许多多糖利用位点（PUL）。这表明，当（该细菌）在肠道中接触到特定胆汁酸时，它可能能够改变其代谢，特别是其靶向不同复杂聚糖（包括宿主粘蛋白）的能力。这项工作将有助于我们理解如何合理操纵胆汁酸池和微生物群，以在炎症和其他胃肠道疾病的背景下利用碳水化合物代谢。
