Molecular characterization of bacterial communities in algal–bacterial photobioreactors treating piggery wastewaters

Abstract

The influence of the loading rate and the seasonal environmental conditions on the bacterial communities established in High Rate Algal Ponds (HRAPs) treating diluted swine manure was investigated using 16S rRNA Denaturing Gradient Gel Electrophoresis (DGGE) and further phylogenetic analysis. Two HRAPs were successfully operated at different loading rates (10 and 20 times diluted swine manure, resulting in average Surface Organic Loading Rates (SOLR) ranging from 13 to 99gm−2d−1 and from 21 to 180gm−2d−1, respectively) for 9 months. The DGGE analysis revealed a high diversity of bacteria symbiotically living with microalgae. The environmental conditions rather than the organic loading rate were the most significant factors determining the bacterial community structure. Hence, despite a higher biodiversity was recorded in summer, both HRAPs presented a similar community regardless of their different organic loading. Most of the species (≈54%) belonged to Verrucomicrobium, an ubiquitous phylum of aerobic bacteria commonly found in eutrophic environments. Firmicutes and Proteobacteria (Gammaproteobacteria) were the other dominant phyla. Some of the bacteria present in the HRAPs were highly resistant to UV radiation and floc-forming species, which might explain the reasonable good settling characteristics of the algal–bacterial biomass in the ponds. The present work provides new insights on the complex interactions between microalgae and bacteria in algal-based wastewater treatment systems.