Zhejiang University Institute of Preventive Veterinary Medicine and Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, 388 Yuhangtang Road, Hangzhou, Zhejiang 310058, PR China.
Zhejiang Provincial Center for Disease Control and Prevention, 630 Xincheng Road, Hangzhou, Zhejiang 310051, PR China.
Microbiology (Reading). 2011 Nov;157(Pt 11):3150-3161. doi: 10.1099/mic.0.049619-0. Epub 2011 Aug 11.
Listeria monocytogenes is a foodborne pathogen causing listeriosis. Acid is one of the stresses that foodborne pathogens encounter most frequently. The ability to survive and proliferate in acidic environments is a prerequisite for infection. However, there is limited knowledge about the molecular basis of adaptation of L. monocytogenes to acid. Arginine deiminase (ADI) and agmatine deiminase (AgDI) systems are implicated in bacterial tolerance to acidic environments. Homologues of ADI and AgDI systems have been found in L. monocytogenes lineages I and II strains. Sequence analysis indicated that lmo0036 encodes a putative carbamoyltransferase containing conserved motifs and residues important for substrate binding. Lmo0036 acted as an ornithine carbamoyltransferase and putrescine carbamoyltransferase, representing the first example, to our knowledge, that catalyses reversible ornithine and putrescine carbamoyltransfer reactions. Catabolic ornithine and putrescine carbamoyltransfer reactions constitute the second step of ADI and AgDI pathways. However, the equilibrium of in vitro carbamoyltransfer reactions was overwhelmingly towards the anabolic direction, suggesting that catabolic carbamoyltransferase was probably the limiting step of the pathways. lmo0036 was induced at the transcriptional level when L. monocytogenes was subjected to low-pH stress. Its expression product in Escherichia coli exhibited higher catabolic carbamoyltransfer activities under acidic conditions. Consistently, absence of this enzyme impaired the growth of Listeria under mild acidic conditions (pH 4.8) and reduced its survival in synthetic human gastric fluid (pH 2.5), and corresponded to a loss in ammonia production, indicating that Lmo0036 was responsible for acid tolerance at both sublethal and lethal pH levels. Furthermore, Lmo0036 played a possible role in Listeria virulence.
李斯特菌是一种食源性病原体，可引起李斯特菌病。酸是食源性病原体最常遇到的应激源之一。在酸性环境中生存和增殖的能力是感染的前提条件。然而，对于李斯特菌适应酸性环境的分子基础知之甚少。精氨酸脱氨酶（ADI）和胍氨酸脱氨酶（AgDI）系统与细菌耐受酸性环境有关。李斯特菌 I 型和 II 型菌株中发现了 ADI 和 AgDI 系统的同源物。序列分析表明，lmo0036 编码一种假定的氨甲酰基转移酶，含有保守的基序和对底物结合很重要的残基。Lmo0036 作为鸟氨酸氨甲酰基转移酶和腐胺氨甲酰基转移酶起作用，这代表了我们所知的第一个催化可逆鸟氨酸和腐胺氨甲酰基转移反应的例子。分解代谢的鸟氨酸和腐胺氨甲酰基转移反应构成了 ADI 和 AgDI 途径的第二步。然而，体外氨甲酰基转移反应的平衡强烈偏向于合成方向，这表明分解代谢的氨甲酰基转移酶可能是该途径的限制步骤。当李斯特菌受到低 pH 胁迫时，lmo0036 在转录水平上被诱导。其在大肠杆菌中的表达产物在酸性条件下表现出更高的分解代谢氨甲酰基转移活性。一致地，这种酶的缺失会削弱李斯特菌在温和酸性条件（pH 4.8）下的生长，并降低其在合成人胃液（pH 2.5）中的存活能力，并且氨的产生减少，表明 Lmo0036 负责在亚致死和致死 pH 水平下的耐酸能力。此外，Lmo0036 在李斯特菌的毒力中可能发挥作用。
