Labor division of electroactive and carbon degrading microorganisms in bioelectrochemical laminar flow reactors

Abstract

The composition and functions of an anodic microbiome are key to both, successful wastewater treatment on the one and efficient current production on the other hand. How the microorganisms can effectively contribute to these different functions may depend on the type of substrate and the mode of cultivation. In laminar flow bioelectrochemical systems (BES) three different carbon sources with different degrees of complexity were studied, including acetate as benchmark substrate, as well as defined wastewater (DW) and undefined wastewater (unDW) as further substrates. Off-line flow cytometry was used to perform a spatially-resolved analysis of the biofilms in the individual channels of the laminar flow BES. Along the nutrient gradients in the channels, biomass formation was heterogeneous with less biomass in downstream channels which was unfavorable for both, current production and carbon removal efficiency. The microbial compositions of reactors fed with unDW showed more similarities with reactors fed with acetate than with DW. Both, the cytometric α-diversity and intra-community ß-diversity values followed a decreasing (in initial seven channels) and then increasing (downstream channels) overall trend, indicating a reduction in community complexity for all substrates and subsequently the restructuration of the biofilm community. The division of labor between current production and substrate degradation was found to be independent of provided substrates, with some subcommunities performing dual functions as both electroactive microorganisms and carbon degraders. Yet, the degree and efficiency of division of labor, in terms of biomass formation as well as types of subcommunities, was depending on the substrates.