Yan Huicong, Wang Meizhen, Sun Feng, Dandekar Ajai A, Shen Dongsheng, Li Na
School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou, China.
Zhejiang Provincial Key Laboratory of Solid Waste Treatment and Recycling, Hangzhou, China.
Front Microbiol. 2018 Feb 27;9:337. doi: 10.3389/fmicb.2018.00337. eCollection 2018.
uses quorum sensing (QS) to regulate the production of public goods such as the secreted protease elastase. requires the LasI-LasR QS circuit to induce elastase and enable growth on casein as the sole carbon and energy source. The LasI-LasR system also induces a second QS circuit, the RhlI-RhlR system. During growth on casein, LasR-mutant social cheaters emerge, and this can lead to a population collapse. In a minimal medium containing ammonium sulfate as a nitrogen source, populations do not collapse, and cheaters and cooperators reach a stable equilibrium; however, without ammonium sulfate, cheaters overtake the cooperators and populations collapse. We show that ammonium sulfate enhances the activity of the RhlI-RhlR system in casein medium and this leads to increased production of cyanide, which serves to control levels of cheaters. This enhancement of cyanide production occurs because of a trade-off in the metabolism of glycine: exogenous ammonium ion inhibits the transformation of glycine to 5,10-methylenetetrahydrofolate through a reduction in the expression of the glycine cleavage genes , thereby increasing the availability of glycine as a substrate for RhlR-regulated hydrogen cyanide synthesis. Thus, environmental ammonia enhances cyanide production and stabilizes QS in populations of .
利用群体感应（QS）来调节诸如分泌型蛋白酶弹性蛋白酶等公共物品的产生。需要LasI-LasR QS回路来诱导弹性蛋白酶，并使其能够以酪蛋白作为唯一碳源和能源生长。LasI-LasR系统还会诱导第二个QS回路，即RhlI-RhlR系统。在以酪蛋白为食生长的过程中，LasR突变的社会作弊者会出现，这可能导致种群崩溃。在含有硫酸铵作为氮源的基本培养基中，种群不会崩溃，作弊者和合作者会达到稳定的平衡；然而，没有硫酸铵时，作弊者会超过合作者，种群崩溃。我们表明，硫酸铵会增强酪蛋白培养基中RhlI-RhlR系统的活性，这会导致氰化物产量增加，从而控制作弊者的数量。氰化物产量的这种增加是由于甘氨酸代谢中的权衡：外源铵离子通过降低甘氨酸裂解基因的表达来抑制甘氨酸向5,10-亚甲基四氢叶酸的转化，从而增加甘氨酸作为RhlR调节的氰化氢合成底物的可用性。因此，环境氨会增加氰化物的产生，并稳定群体中的QS。
