Cross-feeding interactions in short chain gaseous alkane-driven perchlorate and selenate reduction.

Short chain gaseous alkanes (SCGAs) mainly consist of methane (CH), ethane (CH), propane (CH) and butane (CH). The first three SCGAs have been shown to remove perchlorate (ClO) and selenate (SeO), yet it is unknown whether CH is available to reduce these contaminants. This study demonstrated that CH fed biofilms were capable of reducing ClO and SeO to chloride (Cl) and elemental selenium (Se), respectively, by employing two independent membrane biofilms reactors (MBfRs). Batch tests showed that CH and oxygen fed biofilms had much higher ClO and SeO reduction rates and enhanced expression levels of bmoX and pcrA than that without CH or O. Polyhydroxyalkanoates (PHA) accumulated in the biofilms when CH was supplied, and they decomposed for driving ClO and SeO reduction when CH was absent. Moreover, we revisited the literature and found that a cross-feeding pathway seems to be universal in microaerobic SCGA-driven perchlorate and selenate reduction processes. In the ClO-reducing MBfRs, Mycobacterium primarily conducts CH and CH oxidation in synergy with Dechloromonas who performs perchlorate reduction, while both Mycobacterium and Rhodococcus carried out CH oxidation with perchlorate-respiring Azospira as the partner. In the SeO-reducing MBfRs, Mycobacterium oxidized CH solely or oxidized CH jointly with Rhodococcus, while Burkholderiaceae likely acted as the selenate-reducing bacterium. When CH was supplied as the electron donor, both Mycobacterium and Rhodococcus conducted CH oxidation in synergy with unknow selenate-reducing bacterium. Collectively, we confirm that from CH to CH, all SCGAs could be utilized as electron donors for bio-reduction process. These findings offer insights into SCGA-driven bio-reduction processes, and are helpful in establishing SCGA-based technologies for groundwater remediation.