Effects of substrate composition on the structure of microbial communities in wastewater using fluorescence in situ hybridisation

The microbial composition in a pulp and paper wastewater aerated lagoon system was analysed using fluorescence in situ hybridisation (FISH) to gain further understanding of the effect of substrate composition on microbial diversity for improved management of wastewater treatment systems. Few experiments have been conducted to tease apart the factors influencing the composition and abundance of certain groups within these wastewaters. Specific probes were used to investigate and enumerate the different bacterial groups present at particular stages through the treatment system over an extended period. Community composition and abundance of specific groups differed through the system however temporal stability was retained despite significant variability in the wastewater. Middle stream wastewater samples were enriched to explore the impact of different carbon/nitrogen/phosphorus (C:N:P) ratios on community composition and provide functionality to groups of micro-organisms within the microbial consortia. Nitrogen and phosphorus conditions did not impact community composition of methanol-fed cultures, which exhibited a dominance of Betaproteobacteria (>75%), namely Methylotrophic bacteria. This was confirmed through 16S rRNA gene sequencing and specific FISH probing, reflecting population observations at the beginning of the treatment system. We conclude that the nutrient and carbon combinations used in the enrichments created an interactive effect, altering the community composition and mimicking the main substrate load in the different stages of the treatment system. Finally, pulp and paper wastewater microbial composition was highly variable across the treatment system but was stable within the time sampled, with the enrichments emulating the substrate loads in the full scale system.