Effect Of Light-Irradiation On The Microbial-Driven Manganese Redox Process

Manganese is a major element in nature,and its redox process in the natural environment mainly involves the interconversion of Mn（II）and Mn（IV）mediated by microorganisms.In the existing studies,the light irradiation factors in the surface environment have not been considered.Therefore,this paper intends to study the effect of light on the oxidation of aerobic Mn（II）and reduction of Mn（IV）.Firstly,in the pure water system with Mn（II）and NO₃^-,photochemical manganese oxidation can occur under the irradiation of sunlight,xenon lamp and light shaker.Then,the effect of light on the oxidation process of aerobic manganese in natural river water was studied.The results showed that photochemical manganese oxidation cannot take place in this system,which may be due to the low concentration of Mn（II）and NO₃^-,or the existence of free radical quenchants in river water.However,there was a great difference in the amount of biological manganese oxidation between light and dark systems.When the light intensity was50000 lux,the oxidation rate of Mn（II）can reach 39.27%in 4 days,significantly faster than4.10%in the dark group.Metagenome technology was used to further study the structure and function of microbial community under different conditions.Under light conditions,Aquimonas,Gemmobacter,Alishewanella and Thauera bacteria were significantly enriched,indicating that these bacteria can tolerate photogenic（Reactive oxygen species）ROS.The results of functional gene annotation of KEGG showed that the abundance of manganese oxidation gene mox A was significantly increased under light conditions,and the abundance of genes related to aerobic denitrification and inorganic sulfur assimilation was also increased.It can be seen that although light cannot directly induce the photocatalytic manganese oxidation process in the river system,light can affect the manganese oxidation and N/S metabolism of the community by remodeling the structure and function of the microbial community.Then,the effects of light on the manganese reduction properties of yeast MnRB-1 and Penicillium oxalicum SYJ-1 were studied.26Sr DNA sequencing identified MnRB-1 as Meyerozyma guilliermondii.Compared with SYJ-1,former has strong Mn（IV）reduction property at neutral and low Mn（II）initial concentration,the reduction ability of the latter is stronger when it is acidic and eutrophic.The results of the experiment on the effect of light irradiation on biological manganese reduction showed that the effect of light irradiation on biological manganese reduction was weak.Genome Sequencing and non-target metabonomics studies of MnRB-1 indicate that the main mechanism of manganese oxide dissolution is the solution effect of citric acid.To sum up,the effect of light on the oxidation and reduction of aerobic manganese was investigated.In the biological system tested in this study,light could regulate the manganese oxidation by changing the microbial community structure and function,but had no significant effect on the manganese reduction of two Mn-reducing fungi.These results may provide a new idea for further elucidating the environmental fate of microbial-mediated manganese under illumination.