Characteristics of Streptomyces griseus biofilms in continuous flow tubular reactors

The purpose of this study was to investigate the feasibility of cultivating the biotechnologically important bacterium Streptomyces griseus in single-species and mixed-species biofilms using a tubular biofilm reactor (TBR). Streptomyces griseus biofilm development was found to be cyclical, starting with the initial adhesion and subsequent development of a visible biofilm after 24 h growth, followed by the complete detachment of the biofilm as a single mass, and ending with the re-colonisation of the tube. Fluorescence microscopy revealed that the filamentous structure of the biofilm was lost upon treatment with protease, but not DNase or metaperiodate, indicating that the extracellular polymeric substance is predominantly protein. When the biofilm was cultivated in conjunction with Bacillus amyloliquefaciens, no detachment was observed after 96 h, although once subjected to flow detachment. Electron microscopy confirmed the presence of both bacteria in the biofilm and revealed a network of fimbriae-like structures that were much less apparent in single-species biofilm and are likely to increase mechanical stability when developing in a TBR. This study presents the very first attempt in engineering S. griseus biofilms for continuous bioprocess applications.