Bacteria use small molecule signals to access their local population densities in a process called quorum sensing (QS).Once a threshold signal concentration is reached,and therefore a certain number of bacteria have assembled,bacteria use QS to change gene expression levels and initiate behaviors that benefit the group.Acyl homoserine lactones (AHLs) are a major class of quorum sensing signaling molecules.QS systems are often affected by environmental factors,such as temperature,pH,and nutrient levels,it is hence proposed that the evolution of bacterial cooperation,such as the QS,is rather a dynamic and ever-changing process which is radically affected by environmental conditions,genetic exchanges,as well as by changes in microbial community.