Molecular insight into activated sludge producing polyhydroxyalkanoates under aerobic-anaerobic conditions

One of the options enabling more economic production of polyhydroxyalkanoates compared to pure cultures is the application of mixed cultures. The use of a microbial community in a sequencing batch reactor has a few advantages: a simple process control, no necessity for sterile processing, and possibilities of using cheap substrates as a source of carbon. Nevertheless, while cultivation methods to achieve high PHAs biomass concentration and high productivity in wild and recombinant strains are defined, knowledge about the cultivation strategy for PHAs production by mixed culture and species composition of bacterial communities is still very limited. The main object of this study was to characterize on the molecular level the composition and activity of PHAs producing microorganism in activated sludge cultivated under oxygen limitation conditions. PHAs producers were detected using a PCR technique and the created PHA synthase gene library was analyzed by DNA sequencing. The obtained results indicate that PHAs-producers belonged to Pseudomonas sp., and possessed genes coding for mcl-PHA synthase. The kinetics of mcl-PHA synthase expression was relatively estimated using real-time PCR technology at several timepoints. Performed quantitative and qualitative analysis of total bacterial activity showed that there were differences in total activity during the process but differential expression of various groups of microorganisms examined by using DGGE was not observed.