Extracellular Polymeric Substances Prod- Uction And Its Factors In Landfill Cover Soils And Methanotrophs During CH₄ Oxidation

During CH4 oxidation of landfill cover soils, the accumulation of extracellular polymeric substances (EPS) can inhibit CH4 oxidation activity. EPS are molecules released by microorganisms, which is influenced by many environmental factors. In this study, waste biocover soil (WBS) and Methylosinus sporium were used as experimental materials to investigate EPS production and its influencing factors during CH4 oxidation. Effect of CH4 and O2 concentrations on CH4 oxidation activity, methanotrophic community and EPS production during CH4 oxidation of WBS were characterized. Relationships between CH4 oxidation and soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were analyzed. And effects of environmental factors on CH4 oxidation activity, EPS production and CH4-C distribution during CH4 oxidation were investigated. Main conclusions were listed as follows.(1) As the CH4 exposure time increased, the CH4 oxidation activity of WBS presented a decreasing trend after reaching a peak. When the CH4 concentration was saturated for CH4 oxidation in WBS (i.e. the CH4 concentration of ?10%), the increase of CH4 concentrations could not enhance CH4 oxidation activity. When the CH4 concentration was same, the increase of O2 concentration could promote the CH4 oxdiation activity at the first stage, while the high O2 concentration of 5%-21% could not promote the CH4 oxidation activity at the later stage. In contrast, high O2 concentration would inhibit the CH4 oxidation, due to EPS accumulation.(2) During the CH4 oxidation of WBS, the increase of O2 concentration could promote the production of EPS, including extracellular protein (ECP) and extracellular polysaccharide (ECPS). When the supplyment of CH4 was sufficient (?10%), CH4 concentrations had no obvious effect on EPS production in WBS, while CH4 limitation would promote ECP production in WBS.(3) Type ? methanotrophs Methylocaldum, Methylococcaceae, Methylomicrobium, Methylobacter and type ? methanotroph Methylosinus were abundant in WBS. The methanotrophic community in WBS varied with the difference of CH4 and O2 concentrations. When the O2 concentrations were higher than 5%, Methylocaldum predominated in WBS, while Methylomicrobium had higher abundance under anoxia condition. Methylosinus preferred the environment with high levels of CH4 (10%-50%) and O2 (21%). The importance of environmental variables to the methanotrophic community in WBS followed an order of ECPS> O2> EPS> CH4> ECP, among which only ECPS and O2 concentration had significant effect on the methanotrophic community.(4) The accumulation of EPS had a negative feedback effect on the CH4 oxidation activity ofMethylosinus sporium. During the incubation of Methylosinus sporium, the contents of TB-ECPS and LB-ECP showed negative correlations with the CH4 oxidation activity. When EPS were added into the cultuers, the CH4 oxidation activity decreased with the increase of the EPS addition. The CH4 oxidation activity and the total EPS, S-ECP?S-ECP?LB-ECP?S-ECPS?S-ECPS and LB-ECPS could fit the exponential function well.(5) The EPS production of Methylosinus sporium was affected by various environmental foctors. When pH, temperature, CH4, O2, NO3--VN, Cu2+ concentrations were 6.5-7.5,30-40?,10%-15%,10%,20-140 mg L-1, respectively, the cell growth rate and CH4 oxidation activity of Methylosinus sporium were both high and the productin of EPS was low, and thus was beneficial to sustainable and efficient CH4 oxidation.