Abstract
Quorum sensing is a phenomenon with which bacteria detect high population density and change their phenotype. Bacteria secrete some signal molecules called autoinducer, then detect autoinducer concentration to achieve quorum sensing. Autoinducer-2 (AI-2) is a signal molecule in common use among many bacterial species, and it is synthesized by LuxS . If there is a luxS gene in a bacterial genome, the bacteria may secrete the AI-2. Lactobacillus casei ATCC 334 is a lactic acid bacteria of which the genome has been sequenced completely. It has luxS gene, and AI-2 activity can be detected . In order to study which phenotype is controlled by AI-2 in Lactobacillus casei ATCC 334, we directly added AI-2 to incubate Lactobacillus casei ATCC 334. We purified recombinant protein LuxS and used it to synthesize AI-2 for purification. We used GC-MS and NMR proton spectrum to determine whether the enzyme product was AI-2. We tested the effects of AI-2 on three phenotypes：biofilm、antibacterial ability and antioxidative ability. There is no significant difference.