Catabolite repression by intracellular succinate in Campylobacter jejuni

Bacteria have evolved different mechanisms to catabolize carbon sources from a mixture of nutrients. They first consume their preferred carbon source, before others are used. Regulatory mechanisms adapt the metabolism accordingly to maximize growth and to outcompete other organisms. The human pathogen Campylobacter jejuni is an asaccharolytic Gram-negative bacterium that catabolizes amino acids and organic acids for growth. It prefers serine and aspartate as carbon sources, however it lacks all regulators known to be involved in regulating carbon source utilization in other organisms. In which manner C. jejuni adapts its metabolism towards the presence or absence of preferred carbon sources is unknown. In this study, we show with transcriptomic analysis and enzyme assays how C. jejuni adapts its metabolism in response to its preferred carbon source serine. In the presence of serine as well as lactate and pyruvate C. jejuni represses the utilization of other carbon sources, by repressing the expression of a number of central metabolic enzymes. The regulatory proteins RacR, Cj1000 and CsrA play a role in the regulation of these metabolic enzymes. This metabolism dependent transcriptional repression correlates with an accumulation of intracellular succinate. Hence, we propose a demand-based catabolite repression mechanism in C. jejuni, which depends on the intracellular succinate level. Overall design: Comparison of growth conditions, C. jejuni strain 81116 grown under microaerophilic (5% Oxygen) condition in HI broth compared to C. jejuni strain 81116 grown in HI broth with 25mM serine, or HI broth with 25mM aspartate. Log phase and early stationary phase were examined.

细菌已进化出多种机制，以从混合营养物中降解碳源。它们首先消耗其首选的碳源，然后才利用其他碳源。调节机制根据需要调整代谢，以最大化生长并与其他生物竞争。人类病原体空肠弯曲菌是一种非糖苷分解的革兰氏阴性菌，它通过降解氨基酸和有机酸来促进生长。它偏好丝氨酸和天冬氨酸作为碳源，然而它缺乏已知在调节其他生物碳源利用中的所有调节因子。空肠弯曲菌如何适应其首选碳源的有无尚不清楚。在本研究中，我们通过转录组分析和酶活性测定，展示了空肠弯曲菌如何响应其首选碳源丝氨酸来调整其代谢。在丝氨酸、乳酸和丙酮酸存在的情况下，空肠弯曲菌通过抑制多种中心代谢酶的表达来抑制其他碳源的利用。调节蛋白 RacR、Cj1000 和 CsrA 在这些代谢酶的调节中发挥作用。这种代谢依赖性转录抑制与细胞内琥珀酸的积累相关。因此，我们提出了空肠弯曲菌的一种基于需求的分解产物抑制机制，该机制依赖于细胞内琥珀酸水平。总体设计：生长条件比较，将空肠弯曲菌菌株 81116 在微需氧（5% 氧气）条件下培养于 HI 培养基，与在 HI 培养基中含 25mM 丝氨酸或 25mM 天冬氨酸的培养条件下的空肠弯曲菌菌株 81116 进行比较。观察了对数生长期和早期稳定生长期。