Competition of two highly specialized and efficient acetoclastic electroactive bacteria for acetate in biofilm anode of microbial electrolysis cell

Veerraghavulu Sapireddy,Ali Muhammad,Krishna P Katuri,Pascal E Saikaly

doi:10.1038/s41522-021-00218-3

Veerraghavulu Sapireddy, Ali Muhammad + Show 2 more

Open Access

https://doi.org/10.1038/s41522-021-00218-3

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Abstract

Maintaining functional stability of microbial electrolysis cell (MEC) treating wastewater depends on maintaining functional redundancy of efficient electroactive bacteria (EAB) on the anode biofilm. Therefore, investigating whether efficient EAB competing for the same resources (electron donor and acceptor) co-exist at the anode biofilm is key for the successful application of MEC for wastewater treatment. Here, we compare the electrochemical and kinetic properties of two efficient acetoclastic EAB, Geobacter sulfurreducens (GS) and Desulfuromonas acetexigens (DA), grown as monoculture in MECs fed with acetate. Additionally, we monitor the evolution of DA and GS in co-culture MECs fed with acetate or domestic wastewater using fluorescent in situ hybridization. The apparent Monod kinetic parameters reveal that DA possesses higher jmax (10.7 ± 0.4 A/m2) and lower KS, app (2 ± 0.15 mM) compared to GS biofilms (jmax: 9.6 ± 0.2 A/m2 and KS, app: 2.9 ± 0.2 mM). Further, more donor electrons are diverted to the anode for respiration in DA compared to GS. In acetate-fed co-culture MECs, DA (98% abundance) outcompete GS for anode-dependent growth. In contrast, both EAB co-exist (DA: 55 ± 2%; GS: 24 ± 1.1%) in wastewater-fed co-culture MECs despite the advantage of DA over GS based on kinetic parameters alone. The co-existence of efficient acetoclastic EAB with high current density in MECs fed with wastewater is significant in the context of functional redundancy to maintain stable performance. Our findings also provide insight to future studies on bioaugmentation of wastewater-fed MECs with efficient EAB to enhance performance.

Highlights

The current trend in biological wastewater treatment is moving toward recovery of resources[1,2]
These results suggest that other efficient acetoclastic electroactive bacteria (EAB) such as D. acetexigens might become dominant at the anode when conditions are favorable, supporting functional stability through functional redundancy
It is still not clear what triggers the selection of G. sulfurreducens or D. acetexigens to become dominant at the anode of microbial electrochemical technologies (METs) fed with acetate or domestic wastewater

Summary

INTRODUCTION

The current trend in biological wastewater treatment is moving toward recovery of resources (e.g., reclaimed water for reuse, energy, nutrients, materials, etc.)[1,2]. In METs, electroactive bacteria (EAB) are considered the key functional microbiome responsible for transforming organic (e.g., acetate) or inorganic (e.g., ammonium) pollutants in wastewater into energy through the electrogenesis process at the anode[6,7,8] This is possible because EAB have extracellular electron transfer (EET) capability that allow them to couple the oxidation of substrates (electron donor) in their cytoplasm with the reduction of insoluble extracellular electron acceptors (e.g., electrode) for respiration[9]. For the successful application of METs for domestic wastewater treatment, it is important to first investigate whether highly specialized and efficient acetoclastic EAB competing for the same resources (electron donor and acceptor) co-exist in the anode biofilm. D. acetexigens was detected along with G. sulfurreducens in the anodic biofilms enriched from mixed-culture inoculums, such as anaerobic sludge[21], domestic sewage[10,22], raw paper mill effluents[23], and lagoon sediment[24]

RESULTS

Sapireddy et al 3 a b

DISCUSSION