Estimation of dominant microbial population sizes in the anaerobic granular sludge of a full-scale UASB treating streptomycin wastewater by PCR-DGGE

Although the dominant members of microbial communities in wastewater bio-treatment systems were often paid attention due to their possible important roles in treatment performance, their population sizes, especially the unculturable species, were still little known. Then PCR-DGGE was used in an attempt to estimate the dominant microbial population sizes in the anaerobic granular sludge treating streptomycin wastewater, coupled with an inoculated strain (Esherichia coli) with known population sizes as an internal standard. The results indicated that the band intensities of the inoculated strain in DGGE profiles showed good correlation with population sizes. Then it was possible to estimate the dominant microbial population sizes by means of comparing their DGGE band intensities with the inoculated strain. The estimated results demonstrated that the sizes of major dominant microbial populations in the sludge sample were at the level of 10⁷–10⁸ CFU/g. The sizes of secondary dominant microbial populations were at the level of 10⁵–10⁶ CFU/g. The microbial populations with the size level lower than 10³ CFU/g were undetectable by PCR-DGGE. These results provided a potential approach to evaluate dominant microbial population sizes in complex microbial communities.