Characterization of secondary microbial communities in industrial bioreactors producing high value chemicals
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Microbial communities are key drivers of biogeochemical cycles and several important industrial processes rely on complex, undefined microbial ecosystems for production or conversion of substrates for example in wastewater treatment or anaerobic digestion plants. Despite their significance, such communities are often poorly defined, if at all. This project concerned previously undefined secondary microbial communities (SMCs) from photobioreactors culturing cyanobacterium Arthrospira platensis, known for producing high-value protein-pigment complex C-phycocyanin (C-PC). C-PC has a range of applications in the biochemical/pharmaceutical and food industries. Next-generation sequencing methods were applied to characterize the SMCs sampled over the course of various batch runs. The bioreactor exerted a strong selective pressure on the SMC, initially diverse and dynamic, succeeded by a stable and predictable SMC dominated by a few species. SMC stability and diversity correlated with reactor performance, especially proliferation and instability of the rare-abundance sub-population; dominant species ratios were likely less important. The substantially larger (compared to other species present) A. platensis filaments may represent a dynamic microenvironment in itself, and if so, constitutes a significant parameter when optimizing culture conditions. Denser and carefully pre-acclimated inocula reduce the ecological space available to undesirable taxa (e.g. pathogens) otherwise below detectable/significant limits. This has implications for other processes that rely on mixed cultures and may be a control strategy in manufacturing active pharmaceutical ingredients to cGMP standards. Molecular data was used to obtain several pure isolates which were characterized further. Strategies to optimize performance with respect to SMCs were explored and evaluated. A significant aspect of this CASE project was an industrial placement with Scottish Bioenergy. The placement involved set-up of a production facility and incremental scale-up of cultivation from 2 L to 1000 L reactors; development of a downstream processing protocol covering harvesting, pigment extraction and protein purification, and some formulation/stability testing. A very low-cost method is described for obtaining relatively high-purities of C-PC, broadly considered the most costly part of the entire production process.