Isolation And Manganese Oxidation Mechanism Of Novel Mnii-oxidizing Bacteria Based On Microbial Culturomics

Mn^II-oxidizing microorganisms catalyze the formation of Mn oxides from Mn^II,which can enhance the degradation of trace organic pollutants in water treatment systems(such as manganese sand filters and wetlands)and the anaerobic oxidation of methane from sediment,thus being widely studied.The isolation of Mn^II-oxidizing bacteria with different ecological niches from the environment is an important basis for the bioaugmentation of the Mn^II-oxidizing process in the environment.However,the existing isolation methods of Mn^II-oxidizing strains often use a single medium with a high concentration of nutrients to enrich and separate functional microorganisms,cultivate concentration is much higher than the nutrient concentration in the environment,excessive nutrition can inhibit the growth of even stop microorganisms,cause can develop low manganese oxide bacterial diversity and strain separation efficiency is low.Culturomics is a powerful method for the isolation of microbial strains by establishing a variety of culture conditions to increase the probability of the isolation of functional strains.In order to explore and understand the microorganisms leading to Mn^II-oxidizing at various concentrations,and clearly understand the microbial mechanism in the process of Mn^II-oxidizing,so as to achieve efficient separation of Mn^II-oxidizing strains,the microbial diversity and community structure composition at various concentrations were analyzed.The results showed that there was a certain abundance of Mn^II-oxidizing bacteria in the culture system with low nutrient concentration(e.g.,PYG culture media diluted 5 to 625 times),and a drastic community succession occurred during the culture process,and the microbial diversity was also higher than that in the culture system with high nutrient concentration.According to the potential preference of Mn^II-oxidizing strains for low concentration of nutrients,a common Mn^II-oxidizing bacteria medium was gradient diluted to prepare five culture media with lower concentrations of nutrients.A total of27 strains of Mn^II-oxidizing bacteria were isolated,and some rare Mn^II-oxidizing bacteria were also isolated,such as Mn^II-oxidizing bacteria which has not been reported in domestic literature,include Pseudoxanthomonas ? Hydrogenophaga ?Exiguobacterium and unreported Mn^II-oxidizing strains include Chryseobacterium?Cupriavidus?Enterobacter.The results showed that 89% of these rare and unreported Mn^II-oxidizing bacteria were isolated from the diluted culture system,compared with the original medium,Mn^II-oxidizing strains of additional 6 genera were isolated from the four diluted culture media,improving the isolation efficiency of Mn^II-oxidizing strains.In this reaserch an isolated Pseudoxanthomonas Mn^II-oxidizing strain(Pseudoxanthomonas mexicana S5-3-5X)was firstly reported in Chinese pieces of literature.The strain could grow under typical environmental conditions(p H 6.0~7.8;low nutrient concentration(e.g.,PYG culture media diluted 5 to 625 times);Mn^II concentrations range from 50 ?mol/L to 1.6 mmol/L)and generate Mn^II-oxidizing activity.The strain produced Mn^II-oxidizing activity by producing both extracellular superoxide radical and Mn^II-oxidizing protein.Its genome encoded three Mn^IIoxidizing protein homologs of a Mn^II-oxidizing type stain Pseudomonas putida GB-1and has metabolic pathways for degrading some organic pollutants.