Bacterial Community Structures Of Granule Sludges Under Two Different Carbon Source Conditions

Aerobic granule sludge has many important properties such as excellent settleability and high microbial density, and hence can be used for the efficient removal of nitrogen and phosphorus from wastewater. Previous studies have shown that the composition of carbon sources can greatly affect the efficiency of nitrogen and phosphorus removal by granule sludge. However, these studies mainly focused on the physicochemical properties and the internal structures of granule sludge. Up to now, little is known about the effects of carbon sources on the composition of bacteria in granule sludge, especially those with special function. In this thesis, we analyzed the bacterial structures of aerobic granule sludges using 16 S rDNA clone libraries in two sequencing batch reactors(SBR) whose carbon sources are glucose and wastewater from white wine production, respectively. We also compared the diversity of bacteria and their functions in granule sludge under the two different carbon source conditions. The main research contents and results are reported as follows:(1) Two libraries were constructed respectively and 155 positive clones were obtained in each library. According to the RFLP results, the two liabraries were divided into 53(glucose library) or 90(white wine wastewater library) operational taxonomic units(OTU) respectively. Schao1 of glucose library is 89.2, while that of white wine wastewater library is 183.2. Granule sludge cultured with white wine wastewater has higher bacterial diversity than that cultured with glucose, which indicates that the composition of inflow influences the bacterial diversity of granule sludge significantly.(2) One representive clone was selected and sequenced from each OTU which contains more than one clones, and 26(glucose library) or 30(white wine wastewater library) 16 S rDNA sequences were obtained. Phylogenetic analysis results indicate that clones which have been sequenced in white wine wastewater library belong to Proteobacteria, Acidobacteria, Chloroflexi and Bacteroidetes. Besides these four phyla, bacteria from two other phyla, Candidatus Saccharibacteria or Planctomycetes were also detected in glucose library.(3) Significant differences have been found in bacterial community structures between the two libraries at genus level. In glucose library, Candidatus Accumulibacter which accounts for 23.4% is the only dominant group that can be identified to the genus level. Other dominant groups share low sequence similarity with cultured bacteria, and they constitute 5.5%~8.6% of sequenced clones in glucose library. The dominant groups of white wine wastewater library are mainly from 4 genera(Thauera, Dechloromonas, Nitrosomonas and Hydrogenophaga), which account for 16.8%, 8.4%, 8.4% and 5.3% of sequenced clones respectively. Furthermore, there are also some clones which share low sequence similarity with cultured bacteria(5.3%~8.4% of sequenced clones). The differences of dominant groups between the two libraries indicate that carbon soures has great influence on bacterial community structure of granule sludge.(4) Bacteria that may involved in N or P removal were detected in both libraries. These two libraries have the same phosphorus-accumulating bacteria(Candidatus Accumulibacter) which accounts for 23.4% in white wine wastewater library and just 8.4% in glucose library. Just one group of denitrifier(Denitratisoma-like bacteria) was detected in glucose library. However, denitrifiers including Sulfuritalea-like bacteria, Thauera, Dechloromonasand Zoogloea were detected in white wine wastewater library. Furthermore, the ratio of denitrifiers in white wine wastewater library(29.5%) is higher than that in glucose library(7.0%). This may due to the differences in N and P load as well as composition of inflow in the two SBRs.(5) Bacteria that can degrade aromatic compounds, oxidize ammonia or secrete EPS(Extracellular Polymeric Substances) were decteded in white wine wastewater library, however, they were not found in glucose library. These results indicate that the aerobic granule sludge cultured with white wine wastewater is more applicable to treat complex organic wastewater due to its richer functional diversity of bacteria.