Bidirectional extracellular electron transfers by Stenotrophomonas sp. and by Serratia marcescens via tunable extracellular polymeric substances at low or at high solution conductivity

Abstract

Unearthing robust electrochemically active bacteria (EAB) with bidirectional extracellular electron transfer (EET) is increasingly attractive for the treatment of wastewaters characterized by a diversity of ions and limited by either carbon/electron sources or electron acceptors in single-chamber bioelectrochemical systems (BESs). Here, both Stenotrophomonas sp. YS1 and Serratia marcescens Q1 biofilms were demonstrated to be switchable and thus capable of bidirectional EET metabolizing either organic (acetate) or inorganic species (NaHCO3) in single-chamber BESs. The electron uptake (inward EET) by Q1 was more efficient than that of YS1 while, YS1 was more efficient than Q1 for outward EET. Higher solution conductivity significantly increased the EET activities of both strains, although, Q1 was more affected than YS1 during outward EET, while YS1 was more impacted than Q1 during inward EET. Experiments performed at low (5.8 mS/cm) and at high (103 mS/cm) solution conductivity with inward and outward EET evidenced the variable amount and compositional diversity of extracellular polymeric substances (EPS) released by Q1 and YS1 biofilms and plankton cells during inward or outward EET, demonstrating the regulative manipulation of these EAB via adaptive electrochemically-tunable EPS components. This study demonstrates EET between Stenotrophomonas sp. or S. marcescens and the electrodes is bidirectional and switchable with dependence on solution conductivity via the response of EPS amount and compositional diversity, giving a comprehensive appreciation of the bacteria behaviour through tunable EPS in response to the altered solution conductivity widening our knowledge on EAB bidirectional EET in single-chamber BESs.