Hypoxic Energy Metabolism Of Different Functional Bacteria In Methane-oxidizing Community

With the advancement of industrialization and urbanization,methane,the content of greenhouse gas in the atmosphere,has gradually increased.Methane oxidizing community is a key part of controlling methane balance in the atmosphere.Therefore,in-depth study of the metabolic process of methane-oxidizing community will be helpful for providing a theoretical basis for controlling the greenhouse effect.Methaneoxidizing community takes across redox gradients,crossing hyperoxia,hypoxia and anoxia,and especially at the interface of hyperoxia-hypoxia.Metagenomic analysis shows that the traditional aerobic methane oxidizing community is active in the hypoxic niche.However,the mechanism of hypoxic energy metabolism by aerobic methaneoxidizing community remains unclear.At the same time,Some researches showed that not only the methane oxidizing bacteria,the accompanying bacteria also play an important role in the material and energy flow of microbial methane oxidation.In this study,ferrihydrite was used as the electron acceptor for the traditional aerobic methaneoxidizing community,to study the energy metabolism strategy of community in hypoxic niche;evaluate the contribution of methanotroph and accompanying bacteria to the energy flow;and analyze the hypoxic energy metabolism mechanism of typical accompanying bacteria in hypoxic condition.The main contents are as follows:(1)Ferrihydrite could be an alternative electron acceptor for methane-oxidizing community under hypoxic conditions.According to the electron transfer calculation,the contribution ratio of methanotroph and accompanying bacteria during iron reduction was 1:3,which indicates that the accompanying bacteria in the methaneoxidizing community play an important role in the microbial methane oxidation coupled with the iron cycle.Based on metagenomic analysis,the companion bacteria in community include Methylophilus,Acinetobacter and Pseudomonas,which provides a direction for the subsequent exploration of energy metabolism of typical companion bacteria.(2)Based on the Methylophilus sp.YYY-1 strain isolated from the methaneoxidizing community,the iron reduction rate of Methylophilus sp.YYY-1 strain under hypoxic condition was 53.6 ?MFe(?)/d.The bioelectrochemical technology and genomic analysis,showed that extracellular iron reduction was mediated by cytochrome c and riboflavin.Glucose may be a key intermediate metabolite that drives the iron reduction of Methylophilus sp.YYY-1 after metabolic processes analysis.This study revealed the hypoxic energy metabolism of Methylophilus sp.YYY-1,and provided a survival strategy in "hypoxic-hyperoxic" niche.(3)Based on the Acinetobacter sp.YYY-2 and Pseudomonas sp.YYY-3 strains isolated from the methane-oxidizing community,the iron reduction rates under hypoxia were 126 ?MFe(?)/d and 64.8?MFe(?)/d respectively.The redox peaks of Acinetobacter sp.YYY-2 and Pseudomonas sp.YYY-3 were 8 and 6 times higher than those of Methylophilus sp.YYY-1,respectively.The stronger extracellular electron transport capacity determines the faster iron reduction of Acinetobacter sp.YYY-2 and Pseudomonas sp.YYY-3.Mineral characterization shows that the iron was still spherical but the particle size was significantly increased after reduction,unlike the flake magnetite formed by Methylophilus sp.YYY-1.This study revealed the energy metabolism and biological mineralization characteristics of heterotrophic bacteria in methane-oxidizing community under hypoxic condition,and extended the carbon-iron coupling process of the methane-oxidizing community in the biogeochemical cycle.