Streamer formation dynamics with mixed bacterial species: Effects of cultivation conditions, hydrodynamics, and species

Most bacterial species synthesize extracellular polymeric substances (EPS) with diverse compositional, structural, and functional characteristics. When under sustained hydrodynamic flow, bacteria form streamers, which are filamentous matrix structures porous in nature. So far, investigations on streamers have been limited to pure culture bacterial species, overlooking the aggregate nature of bacterial flocs and biofilms. The aim of this work is to analyze the effects of the cultivation conditions (controlling the EPS synthesis), the hydrodynamics, and the bacterial species type on streamer formation by pure and mixed culture using microfluidic separators. Enterobacter A47 (EPS-producing bacterium) and Cupriavidus necator (non-EPS producing bacterium) are used for the experimental work. It has been found that the EPS secreted by the bacteria and flow conditions play a very significant role in streamer formation dynamics. Strong flow conditions (i.e., high flow rates and small constrictions with tortuous architecture) favor the fast development of streamers, whereas intermediate flow rates result in sustained growth for longer filtration times, leading to dense streamers. Our analysis confirms that the presence of EPS in the bacterial suspension critically controls streamer formation by forming bacterial aggregates, or flocs, and bridging between different aggregates. We also found that streamer formation is significantly enhanced with mixed bacterial culture, which may be attributed to the symbiotic relationships influencing the concentration and characteristics of EPS and the material behavior in general.