Biofilm Formation Characteristics And Biological Mechanism In Marine Purple Sulfur Bacterium Marichromatium Gracile YL28

Bacterial biofilm is a highly clustered structured community,whose formation process is related to the regulatory system?quorum sensing,second messenger,etc.?involved by various signal factors?bacterial density,light intensity,metal ions and oxygen concentration,etc.?.It has attracted much attention in medicine,marine biofouling and environmental protection due to its unique characteristics and adaptability.At present,the strains applied in water pollution treatment are mainly freshwater or terrestrial strains,which are difficult to adapt to the high-salt environment,and only a few bacteria can form biofilms in the culture system with low ability and limited application value.It is necessary to develop the salt-tolerant strains which can be applied to complex water.Marichromatium gracile YL28 with high efficiency nitrogen removal ability,derived from mangroves was used in this research to optimizes the conditions of its biofilm formation and explore the law of biofilm formation.The effects of single and complex heavy metal ions?HMIs?on the characteristics of biofilm in M.gracile YL28 were investigated.In addition,the denitrification effect of the biofilm in wastewater containing HMIs and its adsorption capacity to HMIs were further investigated.The control mechanism of biofilm-formation was preliminarily investigated by constructing the biosensor of c-di-GMP.The main results are as follows:·M.gracile YL28 biofilm formation and its characteristics.M.gracile YL28 was treated with 8 factors necessary for its growth?using dehydrogenase activity as the indicator?.The factors affecting the formation of M.gracile YL28 biofilm were screened by P-B?Plackett-Burman,P-B?and o Response Surface Methodology.The formatted biofilm limited light intensity in the cultured system,but the dehydrogenase activity of the internal free bacteria did not decrease and removal activity of ammonia nitrogen and nitrite was not affected.So a new model of APB biofilm formation was initially proposed---the bacteria in the medium are mainly grown in the biofilm and its interface and spread to the culture medium.·Effect of single HMIs on biofilm properties.HMIs had a negative effect on formation,bioactivity and pigment synthesis of biofilm.In the range of selected HMIs,biofilm tolerance to HMIs was higher than plankton and can adsorb higer level of HMIs.HMIs could inhibit the synthesis of YL28 photosynthetic pigment,and decrease the level of synthesis forthe total amount of BChl a and Car.With the increaseing concentration of HMIs,protein and polysaccharide showed a tendency that rising and then decreasing,but the concentration of peak was different.·Effects of multivariate HMIs on biofilm properties and removal of HMIs by biofilm.In the medium containing multivariate HMIs,the activity of inorganic nitrogen removal was not affected,but the capacity of protein secretion was inhibited.The binary and ternary interaction test between multivariate HMIs manifested that antagonism between (Cu²⁺*Hg²⁺)or interaction (Cu²⁺*Zn²⁺).Quaternary,pentabasic and six-membered interaction test of HMIs for biofilm showed the interactive inhibition between most effectors.In biofilm bioreactors containing HMIs and inorganic nitrogen?8 d?,the removal rates of high?H?and low?L?level HMIs were Cd²⁺?55.20%,73.10%?,Cr⁶⁺?74.30%,91.10%?,Cu²⁺?57.60%,74.60%?,Pb²⁺?44.3%,90.8%?,Zn²⁺?38.70%,41.10%?and Hg²⁺?31.70%,33.80%?,but nitrate and nitrite removal were not affected.In the experimental process of cultured water body,it was found that YL28 showed the interaction with the native microorganisms to reduce the content of inorganic nitrogen in water body.·Preliminary study on the regulatory mechanism of biofilm formation.The excavation analysis of key genes preliminarily mapped the metabolic pathways for c-di-GMP regulating biofilm formation.E.coil?pVLT33-FRET-YcgR?was constructed to detect varied level of c-di-GMP.Environmental factors affects the growth of the strain and the secretion of c-di-GMP,which also lays a foundation for the comprehensive exploration of the biofilm formation mechanism of M.gracile YL28.In summary,this study found that the YL28 has a high biofilm formation rate.The influence and law of environmental factors on biofilm formation are expounded.A new biofilm formation model of APB strain was proposed.To elucidated the biological activity and biofilm-forming mechanism of YL28 in the complex environment of single and HMIs.It provides a method for comprehensively analyzing the effects of environmental factors on biofilm formation.The preliminary application of YL28 biofilm has obvious removal effect in high inorganic nitrogen simulation water.Provide reference strains for the development and application of biofilm reactors.At the genomic level,the regulatory mechanism was initially analyzed,which laid the foundation for further research.