Thornhill Starla G, Kumar Manish, Vega Leticia M, McLean Robert J C
Department of Biology, Texas State University, 601 University Drive, San Marcos, TX 78666, USA.
NASA Human Research Program (HRP) NASA-Johnson Space Center, 2101 E NASA Pkwy, Houston, TX 77058, USA.
Microbiology (Reading). 2017 Oct;163(10):1429-1435. doi: 10.1099/mic.0.000531. Epub 2017 Sep 12.
Single-celled bacteria are capable of acting as a community by sensing and responding to population density via quorum signalling. Quorum signalling in Chromobacterium violaceum, mediated by the luxI/R homologue, cviI/R, regulates a variety of phenotypes including violacein pigmentation, virulence and biofilm formation. A number of biological and organic molecules have been described as quorum signalling inhibitors but, to date, metal-based inhibitors have not been widely tested. In this study, we show that quorum sensing is inhibited in C. violaceum in the presence of sub-lethal concentrations of cadmium salts. Notable Cd-inhibition was seen against pigmentation, motility, chitinase production and biofilm formation. Cd-inhibition of quorum-signalling genes occurred at the level of transcription. There was no direct inhibition of chitinase activity by Cd at the concentrations tested. Addition of the cognate quorum signals, N-hexanoyl homoserine lactone or N-decanoyl homoserine lactone, even at concentrations in excess of physiological levels, did not reverse the inhibition, suggesting that Cd-inhibition of quorum signaling is irreversible. This study represents the first description of heavy metal-based quorum inhibition in C. violaceum.
单细胞细菌能够通过群体感应来感知并响应群体密度，从而表现出群体行为。紫色杆菌中的群体感应由luxI/R同源物cviI/R介导，可调节多种表型，包括紫色素产生、毒力和生物膜形成。已有多种生物和有机分子被描述为群体感应抑制剂，但迄今为止，金属基抑制剂尚未得到广泛测试。在本研究中，我们发现，在亚致死浓度的镉盐存在下，紫色杆菌中的群体感应受到抑制。在色素产生、运动性、几丁质酶产生和生物膜形成方面观察到了显著的镉抑制作用。镉对群体感应基因的抑制作用发生在转录水平。在所测试的浓度下，镉并未直接抑制几丁质酶活性。即使添加同源群体信号N-己酰基高丝氨酸内酯或N-癸酰基高丝氨酸内酯，即使其浓度超过生理水平，也无法逆转这种抑制作用，这表明镉对群体感应的抑制作用是不可逆的。本研究首次描述了紫色杆菌中基于重金属的群体抑制作用。
