Bidirectional extracellular electron transfers in Serratia marcescens and Stenotrophomonas sp. correlate to EPS and Cr(VI) removal in single-chamber bioelectrochemical systems

BACKGROUND

Electrochemically active bacteria (EAB) capable of bidirectional extracellular electron transfer (EET), either outward or inward EET, largely control the efficiency of interactions and electrical communication between biofilm and electrode and, thus, control the performance of bioelectrochemical systems (BESs) for heavy metals removal. However, the behavior of such metallurgical EAB capable of bidirectional EET has yet to be investigated, and the role of extracellular polymeric substances (EPS) in these switchable EAB with bidirectional EET and in the presence of heavy metals remains unexplored in the single-chamber BESs treating heavy metal-based wastewaters that are limited by carbon/electron sources or electron acceptors.

RESULTS

The biofilms of the Cr(VI)-tolerant EAB Stenotrophomonas sp. YS1 and Serratia marcescens Q1 exhibited bidirectional EET metabolizing either organic (acetate) or inorganic (HCO₃⁻) species with simultaneous removal of Cr(VI) in single-chamber BESs. Q1 inward EET uptake of electrons was more efficient than that of YS1 (165 μA vs. 118 μA); meanwhile, YS1 outward EET was more efficient than Q1 (8.0 μA vs. 4.7–5.2 μA). The adaptive electrochemically-tunable EPS in both biofilm strains was regulated by the direction of the EET (inward or outward) in the presence of Cr(VI) and circuital current.

CONCLUSION

This study demonstrates the switching properties of EAB, such as Stenotrophomonas sp. or S. marcescens, that are capable of bidirectional EET to or from the electrodes, and it displays the regulation of such responses with the amount and compositional diversity of the biofilms’ EPS, giving a comprehensive appreciation of tunable EPS for Cr(VI)-wastewater treatment in single-chamber BESs. © 2024 Society of Chemical Industry (SCI).