Methanol-linked synergy between aerobic methanotrophs and denitrifiers enhanced nitrate removal efficiency in a membrane biofilm reactor under a low O2:CH4 ratio

Methane-Oxidizing Activity Enhances Sulfamethoxazole Biotransformation in a Benthic Constructed Wetland Biomat

“…This study established congruency between field-scale metatranscriptomics and laboratory inhibition microcosms in determining that biomat methane oxidation was mediated by the pMMO, enhancing sulfamethoxazole and nitrate attenuation kinetics by up to ∼14× and ∼4× relative to biomat incubations without methane, respectively. Our findings specifically identified Methylococcaceae as conserved agents of this coupled pathway with putative ecological linkages to methylotrophic bacteria (i.e., Methylophilaceae, Hyphomicrobiaceae) similarly observed in engineered bioreactors, natural wetland sediments, and lakes . Moreover, aerobic methanotrophs are ubiquitous in natural wetlands, , rice paddy soils, , and other ecosystems, − and pharmaceuticals have been observed in various environments worldwide .…”

“…(RS202); Burkholderiales ord., JAEUMW01 fam. (RS207); NCBI: Burkholderiales bacterium] is less compelling than all other microcosm ASV to field MAG linkages (Table S3), Methylophilaceae are well known to facultatively conduct methylotrophic denitrification, ,− and their ecological association with Methylococcaceae is well documented. , Considering all of this, we infer that Methylophilaceae and Hyphomicrobium were active in methanol oxidation coupled to an uncertain combination of oxygen and nitrate respiration in our methane-oxidizing microcosms, and that both may contribute more to methylotrophic denitrification in field-systems where microenvironments and oxic–anoxic dynamics persist.…”

“…Methanol has been proposed as the most favorable cross-feeding substrate to support methylotrophic denitrification, and thermodynamic and electron balance estimates suggest that as much as ∼60 to 66% of methanol produced from aerobic methane oxidation is available for methylotrophic denitrifiers. , Thus, the maximum methanol available from low (∼1600 μmoles from ∼2400 μmoles methane) and high (∼3000 μmoles from ∼4600 μmoles methane) methane-oxidizing conditions implies the theoretical possibility of methanol oxidation coupled to the respiration of ∼80 μmoles nitrate (Figure ). However, given that our methane-oxidizing microcosms presumably maintained an oxygen/methane ratio > 1 and that bioreactors using methane oxidation synergistically with denitrification reported mixed proportions of denitrification and assimilation at oxygen/methane ratios < 1, , and with the most favorable conditions for denitrification proposed at an oxygen/methane ratio of 0.25, we anticipate that methanol was predominantly oxidized by methanotrophs and codependent methylotrophic bacteria via oxygen rather than nitrate. Of note, our field Methylotetracoccus MAG did not encode or transcribe nitrate respiring genes known to methanotrophs (i.e., narGH ). , …”

Methane Oxidation Coupled to Selenate Reduction in a Membrane Bioreactor under Oxygen-Limiting Conditions

“…16S rRNA gene sequencing results suggested that the type-II aerobic methanotroph Methylocystis, actively predominant in the enriched methanotrophic communities, coexisted with several potential heterotrophic selenate-reducing bacteria (dominated by Acidovorax and Denitratisoma). Numerous environmental studies have evidenced the widespread occurrence of aerobic methanotrophs in various environments under oxygen-limiting conditions. ,,− In methane-driven ecosystems, these methanotrophs are often found in close association with specific nonmethanotrophic bacteria, ,, among which aerobic methanotrophs are considered as a primary carbon producer via partial methane oxidation and form a synergistic consortia with cohabiting heterotrophs. − These heterotrophs thrive on obtaining carbon and energy from methane-derived organic metabolites such as methanol, formaldehyde, and acetate. , In the aerobic methanotroph–heterotroph association, aerobic methanotrophs would not only provide cross-feeding intermediates to heterotrophs but also create microanoxic niches that favor the growth of syntrophic heterotrophs by releasing oxygen-related challenges like competition for electrons and oxidative stress . Simultaneously, heterotrophs would potentially stimulate methanotrophic activity by preventing the accumulation of toxic and overproduced metabolites of methanotrophs such as methanol and formaldehyde .…”

“…5,7,83−85 In methane-driven ecosystems, these methanotrophs are often found in close association with specific nonmethanotrophic bacteria, 42,86,87 among which aerobic methanotrophs are considered as a primary carbon producer via partial methane oxidation and form a synergistic consortia with cohabiting heterotrophs. 88−90 These heterotrophs thrive on obtaining carbon and energy from methane-derived organic metabolites such as methanol, 91 formaldehyde, 92 and acetate. 45,93 In the aerobic methanotroph−heterotroph association, aerobic methanotrophs would not only provide crossfeeding intermediates to heterotrophs but also create microanoxic niches that favor the growth of syntrophic heterotrophs by releasing oxygen-related challenges like competition for electrons 94 and oxidative stress.…”