Study On The Effect Of Micro And Nano Bubbles On Microbial Carbon Fixation And Related Mechanism

The"greenhouse effect"caused by excessive CO₂emission has caused serious impacts on the global climate and environment,and the fixed CO₂ by biological methods（especially chemoautotrophic microorganisms）has attracted much attention due to its low energy consumption and wide range of environmental adaptation,but its growth rate is slower,resulting in low CO₂ fixation efficiency.Micro and nano bubbles have the characteristics of high mass transfer efficiency and biological effects,and studies have shown that micro and nano bubbles can promote the growth of microorganisms,but there are few studies on the effects of chemoautotrophic microorganisms.Theoretically,micro and nano bubbles have the possibility of combining with autotrophic microorganisms.In order to reduce the harm of CO₂gas to the environment,this study can explore the effect of micro and nano bubbles on the fixation of CO₂ by autotrophic microorganisms.Firstly,the feasibility of adding micro and nano bubbles in different proportions to the medium was explored.On this basis,the effects of micro and nano bubbles of different concentrations and gas sources on the growth and metabolism of autotrophic microorganisms were studied in turn,and the promotion mechanism of micro and nano bubbles on carbon fixation by chemoautotrophic microorganisms was explored by evaluating and analyzing microbial growth amount,physicochemical factors and other indicators.Secondly,micro and nano bubbles were tried to be applied to soil,and the feasibility of their application in soil and their impact on soil microbial mass were evaluated,and the specific research conclusions were as follows:（1）Feasibility of adding in different proportions:combined with the linear regression equation analysis of the addition ratio and the number of micro and nano bubble bubbles,it was found that the R² was above 0.99,which confirmed the feasibility of adding micro and nano bubbles in different proportions,and its effect on the physical and chemical factors of the microbial culture medium also varied with different gas sources and concentration.（2）Promotion effect of micro and nano bubbles on chemoautotrophic microorganisms:using the effects of different gas sources（CO₂,N₂,O₂ and air）micro and nano bubbles on the growth and metabolism of sinomicrobium oceani WH-15,a chemoautotrophic strain of calvin cycle fixed CO₂,it was found that low concentrations（5%～20%）micro and nano bubbles could promote microbial growth with a maximum increase of 55%（air micro and nano bubbles）,while high concentrations（30%～50%）of micro and nano bubbles inhibited microbial growth with a maximum decrease of-79%（CO₂ micro and nano bubbles）.Micro and nano bubbles can bring reducing power to microorganisms,reduce the metabolic output of microbial extracellular polysaccharides,and high concentrations of micro and nano bubbles lead to enhanced microbial intracellular antioxidant capacity,indicating that micro and nano bubbles of different gas sources improve the efficiency of microbial CO₂ fixation through different mechanisms.（3）Mixed micro and nano bubbles have a positive synergistic effect:using different proportions of CO₂,N₂,O₂ micro and nano bubbles mixtures to explore their effects on the growth of chemoautotrophic microorganisms,it was found that when the total concentration was 10%,the three micro and nano bubbles had a synergistic effect,and the peak of microbial biomass(OD₆₀₀)appeared when a certain type of micro and nano bubbles were dominant.In the vicinity of a certain type of micro and nano bubbles（accounting for more than 75%）with absolute advantages,the positive effect is the largest,when the concentration of one micro and nano bubble is close to 0%,while the concentration of the other two micro and nano bubbles is roughly equal（that is,50%each）,the negative effect is the largest.Although there are positive synergistic effects between different gas source micro and nano bubbles,their promotion effect on microbial growth（maximum positive effect is 42%）is lower than that of single air micro and nano bubbles（maximum positive effect is 55%）,and it is found that the interaction of the three micro and nano bubbles has a greater influence on physicochemical factors through ANOVA.When the concentration of micro and nano bubbles is increased by 20%,there are large differences between the replicate data,indicating that when the number of bubbles is large,the positive synergistic effect between micro and nano bubbles of different gas sources is difficult to stably amplify.（4）Micro and nano bubbles have the possibility of application in soil（enhance microbial activity）:by adding 0%～50%of the four gas source micro and nano bubbles to the soil and investigating their effects on soil microbial biomass and physicochemical factors,it was found that within 0～30 days of culture,the physical and chemical properties of soil were different due to different factors such as gas source and cultivation time,and the peak time of microbial biomass in soil was on the 20th or 25th day,of which the peak microbial biomass in the sample group with 50%N₂ micro and nano bubble was the largest.Compared with the soil without micro and nano bubbles,the soil microbial amount in the micro and nano bubble group increased by 1.45%～82.49%,indicating the feasibility of adding micro and nano bubbles in soil and increasing the soil microbial amount.