Although the GraS sensor kinase of Staphylococcus aureus is known for the sensing of and resistance to cationic antimicrobial peptides (CAMPs), we recently established that it also signals in response to acidic pH, which is encountered on human skin concurrently with CAMPs, antimicrobial unsaturated free fatty acids (uFFA), and calcium. We therefore evaluated how these environmental signals would affect GraS function and resistance to antimicrobial uFFA. Growth at pH 5.5 promoted increased resistance of S. aureus USA300 to linoleic and arachidonic acids but not palmitoleic or sapienic acid. However, enhanced resistance to these C_16:1 uFFA was achieved by supplementing acidic medium with 0.5 mM calcium or subinhibitory CAMPs. Enhanced resistance to uFFA at acidic pH was dependent on GraS and GraS-dependent expression of the lysyl-phosphatidylglycerol synthase enzyme MprF, through a mechanism that did not require the lysyl-transferase function of MprF. In addition to enhanced resistance to antimicrobial uFFA, acidic pH also promoted increased production of secreted proteases in a GraS-dependent manner. During growth at pH 5.5, downstream phenotypes of signaling through GraS, including resistance to uFFA, MprF-dependent addition of positive charge to the cell surface, and increased production of secreted proteases, all occurred independently of acidic amino acids in the extracytoplasmic sensor loop of GraS that were previously found to be required for sensing of CAMPs. Cumulatively, our data indicate that signaling through GraS at acidic pH occurs through a mechanism that is distinct from that described for CAMPs, leading to increased resistance to antimicrobial uFFA and production of secreted proteases.

中文翻译：

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金黄色葡萄球菌GraS传感器激酶响应酸性pH的新功能和信号要求。

尽管金黄色葡萄球菌的GraS传感器激酶以其对阳离子抗菌肽（CAMP）的感应和耐药性而著称，但我们最近确定它也响应酸性pH信号，而酸性pH与CAMP并存于人体皮肤上，不含不饱和的抗菌剂脂肪酸（uFFA）和钙。因此，我们评估了这些环境信号如何影响GraS功能和对抗菌uFFA的抵抗力。pH 5.5下的生长促进了金黄色葡萄球菌USA300对亚油酸和花生四烯酸的抵抗力增强，但对棕榈油酸或烯酸没有抵抗力。但是，增强了对这些C _16：1的抵抗力uFFA是通过在酸性介质中补充0.5 mM钙或亚抑制性CAMP来实现的。通过一种不需要MprF的赖氨酰转移酶功能的机制，在酸性pH下对uFFA的增强抗性取决于赖氨酰和磷脂酰赖氨酸甘油合酶MprF的GraS依赖性表达。除了增强抗微生物uFFA的抗性外，酸性pH值还以GraS依赖性方式促进分泌型蛋白酶的产生增加。在pH 5.5的生长过程中，通过GraS传递信号的下游表型，包括对uFFA的抗性，依赖MprF的正电荷添加到细胞表面，以及分泌的蛋白酶产生增加，均独立于酸性胞外传感器环中的酸性氨基酸而发生。以前发现感应CAMP需要使用GraS。