Salt Tolerant Microbial Mixed Culture For Efficient Degradation Of Polycyclic Aromatic Hydrocarbons Using Analytical Hierarchy Process

In recent years,thanks to the growth of the global economy and the increasing demand for energy,the petroleum industry has developed rapidly.Due to natural disasters,accidents,or improper operations,oil leaks occur during production,transportation,storage,and use,and oil or its products are released into the environment such as soil,groundwater,and the ocean,resulting in pollution of hydrocarbons.Among polycyclic aromatic hydrocarbons(PAHs)are one of the common hydrocarbon pollutants,and have become the focus of research on oil pollution due to their toxicity,mutagenicity,carcinogenicity,non-migration,and difficult degradation characteristics.Biodegradation can achieve cost-effective and environmentally friendly reduction of PAHs in the polluted environment,and has become a preferred treatment method.However,there are still some problems when using biological methods to actually repair PAHs pollution: PAHs pollution is often accompanied by saline and alkaline environments,and the huge osmotic pressure caused by high salinity may lead to severe cytoplasmic dissolution,inhibiting the growth and metabolic activity of microorganisms;A single strain can only degrade one or several types of PAHs,especially when dealing with mixtures containing other pollutants and toxic intermediate metabolites that are difficult to degrade,the complexity of degradation increases,resulting in problems such as low degradation efficiency and long degradation time.Moreover,there is still little research on how to scientifically construct bacterial populations to improve the degradation rate of pollutants.Therefore,it is very necessary to screen repair strains that are highly resistant to salt stress and have high metabolic activity in complex environments,and then provide a method for constructing a highly efficient salt tolerant PAHs degrading bacterial population,improving the degradation ability and rate of microorganisms,thereby more effectively repairing PAHs pollution.In this study,phenanthrene,anthracene,and pyrene in PAHs were used as the sole carbon source,and intertidal sediments were used as a new type of inoculum.Under 3% salinity,salt tolerant degrading bacteria capable of degrading PAHs were successfully screened and isolated.The screened salt tolerant degrading bacteria were identified by 16 S r DNA,and a total of 18 different bacteria were identified,belonging to 10 different genera.18 degrading bacteria have the ability to degrade PAHs.Among them,strain Gor-9,strain Bre-12,strain Phy-14,strain Ery-15,and strain Mib-18 can degrade70.82%,72.71%,81.08%,83.9%,and 55.95% in 7 days,respectively.They are the five bacteria with the strongest degradation rate.Therefore,they can be used as the preferred strains to carry out the construction of a highly salt tolerant and efficient degrading bacterial population.The dominant bacteria are salt tolerant and can utilize glucose for growth and metabolism under salinity of 1% to5%.The utilization rate of strain Gor-9 for glucose ranges from 16.81% to 48.60%,strain Bre-12 for glucose ranges from 32.06% to 69.19%,strain Phy-14 for glucose ranges from 25.99% to 40.80%,and strain Ery-15 for glucose ranges from 39.34% to 58.24%,The utilization rate of glucose by strain Mib-18 ranged from 46.07% to 83.33%;The dominant bacteria have metabolic ability to 31 carbon sources in the Biolog ecological board,but their metabolic activity to carbon sources is somewhat different.The metabolic activity(AWCD value)of the strains are: strain Gor-9(0.64627),strain Bre-12(0.65454),strain Phy-14(0.71548),strain Ery-15(0.72457),and strain Mib-18(0.5555).Based on Analytic Hierarchy Process method,the microbial communities were constructed.The utilization rates of glucose for different groups of bacteria under 1%～5% salinity were as follows:combination 1(41.08%～68.93%),combination 2(24.11%～59.01%);Combination 3(42.73%～47.34%)and combination 4(38.69%～79.81%)enhance the impact resistance of the bacterial population to salinity and make the utilization rate of glucose more stable;Single bacteria cannot utilize 2-hydroxybenzoic acid,phenylethylamine,D-glucosamine,heparin Ι-Erythritol,Lphenylalanine α-Butyruvic acid and other carbon sources,and the bacterial community can use these carbon sources for growth and metabolism.The degradation rate of PAHs by single bacteria on the first day is mostly less than 15%,and the degradation rate of PAHs by bacterial groups ranges from54.98% to 64.02%,which can achieve rapid degradation of PAHs.Among them,combination 4(objective assignment group)has the highest degradation rate of PAHs,which can reach 64.02%;Within 7 days,the degradation rate of PAHs by a single bacterium ranged from 59.95% to 83.90%,and the degradation rate of PAHs by a bacterial group ranged from 79.86% to 88.33%,improving the degradation rate of PAHs.Among them,combination 4(objective assignment group)had the highest degradation rate of PAHs,which could reach 88.33%,and the degradation rate of high cyclic pyrene could reach 85.73%,higher than the degradation effect of a single bacterium(55.95% to 79.9%).Based on AHP hierarchical decision analysis,the microbial community constructed based on objective assignment can greatly improve the degradation rate of PAHs.Therefore,it can be used as a model method to provide a theoretical basis for the construction of microbial communities.