The Development Process,Structure And Metabolic Properties Of Paddy Soil Biofilms In Simulated Environment

Biofilm,as a microbially derived sessile community enveloped in a self-produced extracellular polymeric substances(EPS),are irreversibly attached to biotic and abiotic surfaces.They form extremely diverse and complex structures,and are capable of colonizing almost every environment.Microorganisms in biofilms have advantages in survival and stress tolerance,so biofilms are a fascinating subject,due to their significant roles in the environment,industry,and health.Soil environment is a hot spot for biofilm formation,which is rich in microbial communities and various adsorption interfaces,such as minerals,mineral-organic matter complexes,and plant roots surfaces etc.However,very little is known about the formation,structure,and metabolic activity of biofilms in soils due to its complex composition and structure.In this study,mixed microbial populations from fresh paddy fields were extracted and soil biofilms were cultivated in microplates and artificial soil systems.Biochemical methods such as optical coherence tomography(OCT),confocal laser scanning microscopy(CLSM),attenuated total reflection fourier transform infrared spectroscopy(ATR-FTIR),and microbial respiration metabolic assays were used to explore the biofilm formation,structural and metabolic properties of paddy soils.Get the following conclusions:In our work,the extracted soil mixed microorganisms were cultivated in LB broth.The results showed that the multi-species soil biofilms have high biomass in the air-liquid interface.The development process can be divided into four stages: initial stage(0-12h),logarithmic stage(12-24h),mature stage(24-48h),and lysis stage(48-72h).The thickness and roughness coefficient of soil biofilms increased during the development process,and the their morphology changes from flocculent to reticulate.Simultaneously,the secretion of EPS increased,but the predominant compound in EPS is protein rather than polysaccharide during the early period(0-24h)of biofilm development,which may contribute to the formation of stable biofilm structures.In order to obtain simple soil-like systems of known composition,so-called artificial soils were produced.These soils consist of a mixture of minerals mingled with organic material and inoculated with the soil mixed microbial populations.Combining the resultsof nutrient metabolism rate and SEM images,it was visually verified that the mixed microorganisms formed a micron-scale biofilm structure in the topsoil of high-nutrient artificial soil,indicating that sufficient nutrients are one of the conditions for the formation of soil biofilms.Results also showed that the formation of biofilm increased the soil active microbial content from 0.03% to 0.40%,the carbon source metabolic rate increased by 1.8 times,and the nitrogen source metabolic rate increased by 24.5 times.