No abstract

Cometabolic degradation plays a prominent role in bioremediation of commingled groundwater contamination (e.g., chlorinated solvents and the solvent stabilizer 1,4-dioxane [dioxane]). In this study, we untangled the diversity and catalytic functions of multi-component monooxygenases in Azoarcus sp. DD4, a gram-negative propanotroph that is effective in degrading dioxane and 1,1-dichloroethylene (1,1-DCE). Using a combination of knockout mutagenesis and heterologous expression, a toluene monooxygenase (MO) encoded by the tmoABCDEF gene cluster was unequivocally proved as the key enzyme responsible for the cometabolism of both dioxane and 1,1-DCE. Interestingly, in addition to utilizing toluene as a primary substrate, this toluene MO can also oxidize propane into 1-propanol. Expression of this toluene MO in DD4 appears inducible by both substrates (toluene and propane) and their primary hydroxylation products (m-cresol, p-cresol, and 1-propanol). These findings coherently explain why DD4 can grow on propane and express toluene MO for active co-oxidation of dioxane and 1,1-DCE. Furthermore, upregulation of tmo transcription by 1-propanol underlines the implication potential of using 1-propanol as an alternative auxiliary substrate for DD4 bioaugmentation. The discovery of this toluene MO in DD4 and its degradation and induction versatility renders broad applications spanning from environmental remediation and water treatment to biocatalysis in green chemistry. Importance Toluene MOs have been well recognized given their robust abilities to degrade a variety of environmental pollutants. Built upon previous research efforts, this study ascertained the untapped capability of a toluene MO in DD4 for effective co-oxidation of dioxane and 1,1-DCE, two of the most prevailing yet challenging groundwater contaminants. This report also aligns the induction of a toluene MO with non-toxic and commercially accessible chemicals (e.g., propane and 1-propanol), extending its implication values in the field of environmental microbiology and beyond.

Cometabolic bioremediation is trending for the treatment of 1,4-dioxane (dioxane) and other emerging contaminants to meet stringent regulatory goals (e.g., <10 µg/L) since the biodegradation activities can be fueled by...

The spreading of antimicrobial resistance (AMR) in crops and food products represents a global concern.In this study, we conducted a survey of resistomes in maize rhizosphere from Michigan, California, the Netherland, and South Africa, and investigated potential associations with host bacteria and soil management practices in the crop eld. For comparison, relative abundance of antibiotic resistance genes (ARGs) is normalized to the size of individual metagenomes. Michigan maize rhizosphere metagenomes showed the highest abundance and diversity of ARGs, with the detection of blaTEM-116, blaACT-4/-6, and FosA2, exhibiting high similarity (≥ 99.0%) to those in animal and human pathogens. This was probably related to the decade-long application of manure/composted manure from antibiotictreated animals. Moreover, RbpA, vanRO, mtrA, and dfrB were prevalently found across most studied regions, implying their intrinsic origins. Further analysis revealed that RbpA, vanRO, and mtrA are mainly harbored by native Actinobacteria with low mobility, while a group of dfrB genes are adjacent to the recombination binding sites (attC), which together constitute mobile gene cassettes, promoting the transmission from soil bacteria to human pathogens. These results suggest that maize rhizosphere resistomes can be distinctive and affected by many factors, particularly those relevant to agricultural practices.

The spreading of antimicrobial resistance (AMR) in crops and food products represents a global concern. In this study, we conducted a survey of resistomes in maize rhizosphere from Michigan, California, the Netherland, and South Africa, and investigated potential associations with host bacteria and soil management practices in the crop field. For comparison, relative abundance of antibiotic resistance genes (ARGs) is normalized to the size of individual metagenomes. Michigan maize rhizosphere metagenomes showed the highest abundance and diversity of ARGs, with the detection of blaTEM-116, blaACT-4/-6, and FosA2, exhibiting high similarity (≥ 99.0%) to those in animal and human pathogens. This was probably related to the decade-long application of manure/composted manure from antibiotic-treated animals. Moreover, RbpA, vanRO, mtrA, and dfrB were prevalently found across most studied regions, implying their intrinsic origins. Further analysis revealed that RbpA, vanRO, and mtrA are mainly harbored by native Actinobacteria with low mobility, while a group of dfrB genes are adjacent to the recombination binding sites (attC), which together constitute mobile gene cassettes, promoting the transmission from soil bacteria to human pathogens. These results suggest that maize rhizosphere resistomes can be distinctive and affected by many factors, particularly those relevant to agricultural practices.