| The changes of microbe and physico-chemical parameters were monitored and analyzed in the Guangzhou city segment of Pearl River from January 2009 to December 2010. The results are as follows:1) During the survey period, the mean water temperature were 22.06±5.65℃, 19.88±4.23℃and 21.30±5.00℃, pH 7.43±0.29,7.50±0.22 and 7.37±0.30, salinity 0.30±0.14, 0.25±0.17 and 0.34±0.24, transparency 0.36±0.14 m, 0.38±0.11 m and 0.3±0.09 m, the mean concentrations of total nitrogen 8.33±3.02 mg/L,7.04±5.21 mg/L and 8.78±4.84 mg/L, total phosphorus 0.50±0.35 mg/L, 0.53±0.40 mg/L and 0.56±0.28 mg/L, and chlorophyll-a 76.31±48.13μg/L,46.6±28.21μg/L and 52.79±31.82μg/L at Zhongda, Ersha and Yuzhu sampling sites in the river segment, respectively. The annual mean concentrations of total nitrogen and total phosphorus were over theⅤcategory of environmental quality standard for Chinese surface water.2) The characteristic of microbial biodiversity with high abundance was revealed by the traditional culture methods in the Guangzhou city segment. The abundance of total bacteria is within 3.30×105～5.23×106/mL, cultivable bacteria within 1.3×103～8.7×105cfu/mL, coliform within 1.1×102～1.6×104/mL, and fecal-coliform within 90～9.2×103/mL in the segment, respectively. The quantity of fecal-coliform exceeded theⅤcategory of environmental quality standard for Chinese surface water.3) Optimization of the PCR-DGGE system for water sampling from the Guangzhou city segment of Pearl River was proved to improve the DGGE effects. The microbial DNA fingerprinting about the change of the structure in the optimized conditions in spatial and temporal conditions were analyzed in the segment. The results indicated that the highest characteristic bands were 22, 6 and 26 from the primers of 357f/518r, 357f/907r and 968f/1401r, respectively. The primer 357f/518r was the best resolution, and 968f/1401r was distinguished characteristic band. 4) Quantity One software was applied for identifying the DGGE profiles and analyzing the similarity, richness and Shannon-Weaver index of the samples.The composition of microbial communities was higher similarity in aspect of spatial and temporal distributions, and primers of 357f/518r and 968f/1401r had higher richness and Shannon-Weaver index than 357f/907r.5) The correlations of microbe abundance and physical & chemical factors were significant. At Zhangda port, the correlation of coliforms and salinity was positive significant (p<0.05), the fecal-coliform and salinity was positive significant (p< 0.01) as well as with TN (p<0.05). At Ersha port, the correlation of total bacteria and salinity was positive significant (p<0.01), as well as with total nitrogen and total phosphorus (p<0.01). At Yuzhu port, the fecal-coliform correlated with salinity significant (p<0.05), as well as coliform and total nitrogen (p<0.05). The quantity of characteristic bands in DGGE profile associated with the physical and chemical factors were not significant except temperature, salinity and pH.6) Results of principal component analysis (PCA) showed that environmental indicators selected in present study covering most environmental factors which associated with bacterial structure. Three principal component factors were extracted in three sites respectively, which the cumulative contribution rate was 81.86%, 80.09% and 71.32%. The water temperature, total nitrogen, total phosphorus, chlorophyll-a, salinity, pH and transparency played a very important roles in the changes of bacterial community structure in the segment.7) Cluster analysis and multidimensional scaling analysis (MDS) results indicated the microbial community structure in the river segment had high similarity during the survey period.
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