Research On Bacteria Quorum-Sensing System Regulation To Polyhydroxyalkanoate Biosynthesis

Many bacterial species control and modulate their physiology in response to increases in their population densities in a process known as quorum sensing. QS, an important system, regulates different biological functions in bacteria.Polyhydroxyalkanoates (PHA) , a family of intracellular polyesters synthesized by many bacteria under a specific physical conditions (such as excessive carbon, oxygen, phosphorus , nitrogen, magnesium deficiency, etc.). Apart from the physicochemical and mechanical properties comparable that of chemical polymeric materials, PHAs also have biodegradable, biocompatible, optical activity. PHAs have received increasing attentions because it can replace petrochemical plastics.Does QS control the PHA synthesis in bacterial cells? In recent years, many experimental results strongly hint that bacterial QS system is likely to be involved in the regulation of PHA, but no direct experimental evidence is available so far. In the present study, with the wild type Pseudomonas aeruginosa as original material, using physical and chemical means and molecular biological techniques, the differences of PHA accumulation in wild type strain and its mutants defected with the synthase gene for the individual signal molecule were analysed.It has been found that:1) Compare with the PHA accumulation of wild type,the PHA content was reduced 15% in C4-HSL synthase gene mutant PAO210 (△rhlI), 3-Oxo-C12-HSL synthase gene mutant PAO214 (△lasI) and PAO216 (△lasI/△rhlI) reduced about 50%. These indicated that the quorum sensing system involved in the regulation of PHA biosynthesis and the lasI/lasR system played a major role; 2) The PHA accumulation of wild type PAO1, PAO210 (△rhlI) and PAO214 (△lasI) reduced about 50% when the specific signaling molecule inhibitor——azithromycin was added into culture medium. These indicated that the biosynthesis of PHA was inhibited when the synthesis of signal molecule was inhibited. These also provide the evidence that the quorum sensing system may involve in the regulation of PHA biosynthesis from another aspect; 3) The maxium PHA accumulation of PAO1, PAO210 (△rhlI) and PAO216 (△lasI/△rhlI) were increased by 15%, 23% and 29% when adding appropriate C4-HSL signal molecule, but the PHA accumulation of PAO214 (△lasI) did not show a increasing tendency; 4) the PHA accumulation of PAO1 declined and the PHA accumulation of PAO216 increased when exchanging their supernatant; 5) RT-PCR products for transcription analysis were indicated that phaC1 -the key biosynthetic gene of PHA decline in the quorum sensing system mutants and when supplemented with appropriate signal molecule, its transcription was increased.Based on the above experimental results, we concluded that: in Pseudomonas aeruginosa, the quorum-sensing system up regulates intracellular accumulation of PHA.This results give the direct evidence for the first time that quorum sensing system regulate the biosynthesis of PHA, enrich the function of quorum-sensing and provide theoretical guidance to the PHA productions increasing.