Availability of Nitrite and Nitrate as Electron Acceptors Modulates Anaerobic Toluene-Degrading Communities in Aquifer Sediments

Abstract

Microorganisms are essential in the degradation of environmental pollutants. Aromatic hydrocarbons, e.g., benzene, toluene, ethylbenzene, and xylene (BTEX), are common aquifer contaminants, whose degradation in situ is often limited by the availability of electron acceptors. It is clear that different electron acceptors such as nitrate, iron, or sulfate support the activity of distinct degraders. However, this has not been demonstrated for the availability of nitrate vs. nitrite, both of which can be respired in reductive nitrogen cycling. Here via DNA-stable isotope probing, we report that nitrate and nitrite provided as electron acceptors in different concentrations and ratios not only modulated the microbial communities responsible for toluene degradation but also influenced how nitrate reduction proceeded. Zoogloeaceae members, mainly Azoarcus spp., were the key toluene degraders with nitrate-only, or both nitrate and nitrite as electron acceptors. In addition, a shift within Azoarcus degrader populations was observed on the amplicon sequence variant (ASV) level depending on electron acceptor ratios. In contrast, members of the Sphingomonadales were likely the most active toluene degraders when only nitrite was provided. Nitrate reduction did not proceed beyond nitrite in the nitrate-only treatment, while it continued when nitrite was initially also present in the microcosms. Likely, this was attributed to the fact that different microbial communities were stimulated and active in different microcosms. Together, these findings demonstrate that the availability of nitrate and nitrite can define degrader community selection and N-reduction outcomes. It also implies that nitrate usage efficiency in bioremediation could possibly be enhanced by an initial co-supply of nitrite, via modulating the active degrader communities.

Unravelling the genetic and functional diversity of dominant bacterial communities involved in manure co-composting bioremediation of complex crude oil waste sludge

“…Metagenomic analysis showed that Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes were the predominant phyla present in all the microcosms at day 300. The shared genera between manure-treated and control microcosm included Pseudomonas, Delftia, Methylobacterium, Dietzia, Bacillus, Propionibacterium, Bradyrhizobium, Streptomyces, Achromobacter, Microbacterium and Sphingomonas, some of which has been previously reported in oil-contaminated soils [41,43,45], with several members known for their ability to degrade aliphatic and aromatic hydrocarbons [51,52,53]. Whereas Pseudomonas and Sphingomonas have been previously associated with degradation of LMW PAHs [54,55], fermentative, CO 2 -assimilating and methanogenic microorganisms (Bacillus, Methylobacterium and Achromobacter) are known to be key players in HMW PAH degradation [55].…”

Reconnaissance of Oxygenic Denitrifiers in Agriculturally Impacted Soils

“…A third probable nod gene, HdN1_ nod , was found in the genome of Gammaproteobacterium strain HdN1 ( 5 , 9 – 11 ). Nitric oxide dismutation has been suggested in diverse catabolic functions including the oxidation of methane, long chain aliphatic hydrocarbons, benzene, and toluene ( 11 – 14 ). Our expanding understanding of nod diversity suggests there are more bacteria with nod capacity than the few identified through metagenomics or environmental studies ( 6 , 11 , 12 ).…”

Indole-Acetic Acid Promotes Ammonia Removal Through Heterotrophic Nitrification, Aerobic Denitrification With Mixed Enterobacter sp. Z1 and Klebsiella sp. Z2

“…S1. In addition, the degradation of active aromatic hydrocarbons has been reported to be mutually coupled with the HNAD process (Zhu et al, 2020). While the above reports have revealed some influencing factors, the regulatory mechanism of cell growth and metabolism in the HNAD process remains unclear.…”