Structure of a RecT/Redβ family recombinase in complex with a duplex intermediate of DNA annealing

Proof of ssDNA degraded from dsDNA for ET recombination

The widely used ET recombination requires an ssDNA product degraded by Rac phage protein E588 from dsDNA for strand invasion. However, proof of the ssDNA product is still elusive. The study provided three levels of proof sequentially. The probable ssDNAs degraded by E588 from the fluorescent plus-, minus-, or double-stranded dsDNA pET28a-xylanase exhibited a half fluorescence intensity of the corresponding dsDNAs, equivalent to the E588 degradation nucleotides half that of the total nucleotides degraded from the corresponding dsDNA. The ssDNA product degraded by E588 from the fluorescent minus-stranded dsDNA was confirmed by gradient gel-electrophoresis and two nuclease degradation reactions. Degraded by E588 from the dsDNA pET28a-xylanase that had a phosphorothioated plus-stranded 5'-terminus, the plus-stranded ssDNA product was separated via gel electrophoresis and recovered via a DNAclean kit. The recovered ssDNA product was proven to have intact 5'- and 3'-ends by DNA sequencing analysis. This study provides a solid foundation for the mechanism of ssDNA invasion.

Synthetic Nuclease-Producing Microbiome Achieves Efficient Removal of Extracellular Antibiotic Resistance Genes from Wastewater Effluent

Antibiotic resistance gene (ARG) transmission poses significant threats to human health. The effluent of wastewater treatment plants is demonstrated as a hotspot source of ARGs released into the environment. In this study, a synthetic microbiome containing nuclease-producing Deinococcus radiodurans was constructed to remove extracellular ARGs. Results of quantitative polymerase chain reaction (qPCR) showed significant reduction in plasmid RP4-associated ARGs (by more than 3 orders of magnitude) and reduction of indigenous ARG sul1 and mobile genetic element (MGE) intl1 (by more than 1 order of magnitude) in the synthetic microbiome compared to the control without D. radiodurans. Metagenomic analysis revealed a decrease in ARG and MGE diversity in extracellular DNA (eDNA) of the treated group. Notably, whereas eight antibiotic-resistant plasmids with mobility risk were detected in the control, only one was detected in the synthetic microbiome. The abundance of the nuclease encoding gene exeM, quantified by qPCR, indicated its enrichment in the synthetic microbiome, which ensures stable eDNA degradation even when D. radiodurans decreased. Moreover, intracellular ARGs and MGEs and pathogenic ARG hosts in the river receiving treated effluent were lower than those in the river receiving untreated effluent. Overall, this study presents a new approach for removing extracellular ARGs and further reducing the risk of ARG transmission in receiving rivers.

The Rad52 SSAP superfamily and new insight into homologous recombination

Recent structures of DNA-bound bacterial and phage recombinases provide insights into homologous recombination and suggest relation to the eukaryotic Rad52 and identification of a Rad52 single strand annealing protein (SSAP) superfamily.