Structure And Function Of Microorganisms In Xizi Lake, Hangzhou

The structure and function of microorganisms in Xizi Lake, Hangzhou, were studied during the period from 2001 to 2002. Results showed that in the water body of Xizi Lake, annual average of culturable planktonic ammonifiers and nitrogen fixers were 510 and 236 CFU/mL, respectively; Ammonia oxidizers, nitrite oxidizers, nitrate reducers and denitrifiers were 8.5, 16, 587 and 16 MPN/mL, respectively; Inorganic phosphate solubilizing bacteria (1PB) and organic phosphorus mineralizing bacteria (OPB) were 89 CFU/mL and 37 MPN/mL, aerobic and anaerobic cellulose decomposers were 7 and 5 MPN/mL, respectively. While in the sediment, above 10 groups of microbial communities were 2.27× 105, 7× 104 CFU /g, 6.8× 103, 2.3× 105, 1.1 × 105, 1.01 ×104 MPN/g, 5.15× 104 CFU/g, 3.69× 103 MPN/g, 292 MPN/g and 400 MPN/g, respectively (calculated as dry mud). From seasonal distribution, most of microorganisms were relatively rich in cold winter; From spatial distribution, heterotrophic bacteria were rich at severely polluted Xili subarea, while autotrophic nitrifiers were rich at relatively clear Outer center. Identification of functional bacteria showed predominant ammonifiers were Shewanella, Variovorax, Chryseobacterium, Bacillus or Aeromonas; Among 4 selected nitrogen fixers, one (Azorhizobium caulinodans) belonged to. a -proteobacteria, the other three (Serratia marcescens, Klebsiella pneumoniae and Citrobacter freundii) were Enterobacteriace, which belongs to γ -proteobacteria; 2 nitrate reducers were Aeromonas sp. and Citrobacter sp., respectively. Both of them were γ -proteobacteria. 3 IPB strains closely matched to Bacillus megaterium, Terrabacter tumescen and Janthinobacteriwn lividum. respectively, and 6 OPB strains were Azospirillum sp., Enterobacter aerogenes. Blastobacter aggregates, Staphylococcus epidermidis, Acinetobacter haemolyticus and Cryptococcus sp., respectively. Laboratory tests on phosphorus release abilities of selected bacterial strains showed IPB could liberate more than 50 μ g/mL, while OPB produced less than 2μ g/mL water soluble inorganic phosphorus (WSIP) every day, demonstrating the enzymes participating in solubilization of Ca-P should be constitutive ferments and enzymes concerning with mineralization of lecithin might be inducible catalysts. Low abundance and poor compositions of nitrogen utilizing bacteria suggested poor bacterial diversities and weak self-purification of the lake.For revealing the mechanism of low bacterial biomass in the lake, limiting factors for bacterial growth were studied with pure cultural and natural cultural tests. It was showed that carbon source bacteria could absorb was a more important factor than (NH4) 2SO4 and KH2PO4; and higher pH, rich biomass of phytoplanktons and zooplanktons in water body also restrained the growth of heterotrophic bacteria. It was also showed bacteria growth potentiality in natural water could reach to 105 cfu/mL. In addition, based on the fact that phosphorus is usually the limiting nutrient for nitrogen fixers, a novel method named "nitrogen fixing bacterial growth potential" (NFBGP) test, for evaluating limiting nutrients, was developed. Briefly, the method includes four steps: culturing a sample to the maximum growth of autochthonous microorganism, filtering to remove the original biomass, inoculating the filtrate with certain kind of nitrogen fixing bacterium and determining the bacterial growth potential. With the isolated nitrogen fixing bacterium Azomonas sp. WS6, the limiting nutrients of a eutrophic water sample and a drinking water sample were monitored. The results corresponded well to those from traditional algal growth potential (AGP) test and the bacterial regrowth potential (BRP) test, suggesting that the NFBGP test is a useful method for evaluating environmental quality.