Study In Regulating The Metabolism Of Antibacterial Activity Compounds Of Sponge Associated Marine Bacterium NJ6-3-1 Base On Quorum Sensing

Aiming to the marine associated microorganisms which produce antibiotic natural products, the regulation mechanism of metabolizing antibacterial compounds base on quorum sensing was discussed. The purpose of this study is to understand the biological origin of how marine microorganisms could produce natural products.Through sampling from different environment in the sea, isolation of marine bacteria, extracting their metabolites, their antimicrobial and cytotoxic activities were studied. One sponge associated marine bacterium Pseudoalteromonas piscicida NJ6-3-1 with remarkable biological activities was investigated in this study.We chose marine bacterium NJ6-3-1 in a case study to investigate the relationship between antibacterial activity and bacterial density under various growth conditions. Results demonstrated antibacterial activity correlated closely with cell density. Thus, the marine bacterium NJ6-3-1 could start producing antibacterial compounds but only when cell density reached the threshold value of OD630=0.4.To simulate the natural competitive environment, we monitored the antibacterial activity at low cell density when the species were co-cultured with Staphylococcus aureus. Results demonstrated that some signal molecules existing in the metabolites of S. aureus could induce the production of antibacterial substance from marine bacteria NJ6-3-1 even under low cell density conditions below the required threshold value.To use three kinds of diketopiperazines which is the metabolites of NJ6-3-1 as autoinducer molecules, we monitored the antibacterial activity of marine bacterium NJ6-3-1 at low cell density when the species are co-cultured with these three kinds of diketopiperazines. Results demonstrated that cyclo(L-Phe-L-Val) existing in the metabolites of NJ6-3-1 could induce the production of antibacterial substance from marine bacteria NJ6-3-1 even under low cell density conditions below the required threshold value. The results as described above provide preliminary evidence to support the hypothesis that it has the quorum sensing mechanism in NJ6-3-1, furthermore, the antibacterial activity of NJ6-3-1 was controlled by the quorum sensing system of intraspecies and interspecies fashions.The bacterium NJ6-3-1 was cultured with 30 L media. Through chemical methods, the antibacterial compound was separated and purified. Through NMR and mass detection, the antibacterial compound which regulated by quorum sensing was elucidation to be bis-(2-ethylhexyl) phthalate.This study was stared with isolation of marine bacteria associated with marine organisms, continued with bioactive screening, bacteria identification, secondary metabolites production, compounds separation and the antibacterial activity of NJ6-3-1 was regulated by quorum sensing system. Through these works, the integrated approach to explore the potential of marine bacteria for the production of bioactive metabolites was established and some new evidences of the marine microorganisms as medical origin were provided.