Center for Bio/Molecular Science & Engineering, Naval Research Laboratory Washington, DC, USA.
Center for Bio/Molecular Science & Engineering, Naval Research Laboratory Washington, DC, USA ; School of Systems Biology, College of Science, George Mason University Fairfax, VA, USA.
Front Microbiol. 2013 Dec 11;4:379. doi: 10.3389/fmicb.2013.00379. eCollection 2013.
Melanization due to the inactivation of the homogentisate-1,2-dioxygenase gene (hmgA) has been demonstrated to increase stress resistance, persistence, and virulence in some bacterial species but such pigmented mutants have not been observed in pathogenic members of the Vibrio Harveyi clade. In this study, we used Vibrio campbellii ATCC BAA-1116 as model organism to understand how melanization affected cellular phenotype, metabolism, and virulence. An in-frame deletion of the hmgA gene resulted in the overproduction of a pigment in cell culture supernatants and cellular membranes that was identified as pyomelanin. Unlike previous demonstrations in Vibrio cholerae, Burkholderia cepacia, and Pseudomonas aeruginosa, the pigmented V. campbellii mutant did not show increased UV resistance and was found to be ~2.7 times less virulent than the wild type strain in Penaeus monodon shrimp virulence assays. However, the extracted pyomelanin pigment did confer a higher resistance to oxidative stress when incubated with wild type cells. Microarray-based transcriptomic analyses revealed that the hmgA gene deletion and subsequent pyomelanin production negatively effected the expression of 129 genes primarily involved in energy production, amino acid, and lipid metabolism, and protein translation and turnover. This transcriptional response was mediated in part by an impairment of the quorum sensing regulon as transcripts of the quorum sensing high cell density master regulator LuxR and other operonic members of this regulon were significantly less abundant in the hmgA mutant. Taken together, the results suggest that the pyomelanization of V. campbellii sufficiently impairs the metabolic activities of this organism and renders it less fit and virulent than its isogenic wild type strain.
由于对 homogentisate-1,2-双加氧酶基因（hmgA）的失活导致的黑色素沉着已被证明可提高某些细菌物种的抗应激能力、持久性和毒力，但在哈维氏弧菌属的致病性成员中尚未观察到这种色素突变体。在这项研究中，我们使用 V. campbellii ATCC BAA-1116 作为模型生物，以了解黑色素沉着如何影响细胞表型、代谢和毒力。hmgA 基因的框内缺失导致细胞培养上清液和细胞膜中黑色素的过度产生，该黑色素被鉴定为吡咯黑素。与先前在霍乱弧菌、伯克霍尔德氏菌和铜绿假单胞菌中的研究结果不同，色素突变体 V. campbellii 并未显示出对 UV 抵抗性的增加，并且在斑节对虾致病性测定中比野生型菌株的毒力低约 2.7 倍。然而，当与野生型细胞孵育时，提取的吡咯黑素色素确实赋予了更高的抗氧化应激抗性。基于微阵列的转录组分析表明，hmgA 基因缺失和随后的吡咯黑素产生对主要涉及能量产生、氨基酸和脂质代谢以及蛋白质翻译和周转的 129 个基因的表达产生负面影响。这种转录反应部分受到群体感应调控子的损伤的介导，因为群体感应高细胞密度主调节剂 LuxR 的转录物和该调控子的其他操纵子成员的转录物在 hmgA 突变体中明显较少。总之，结果表明，V. campbellii 的黑色素沉着足以损害该生物体的代谢活性，并使其比其同源野生型菌株适应性差且毒力降低。
