Screening Of M-cresol Degrading Bacteria And Identification Of Its Metabolic Mechanism

Phenolic compounds are common materials in industrial production,and these substances are highly toxic and carcinogenic.Once they enter the natural environment,they will cause serious pollution to water and soils,endangerthe environment and human health and safety.M-cresol is the most difficultly degraded compound among the three isomers of cresol.As m-cresol is a common organic pollutant in coking and printing wastewater,it's difficult for these industrial wastewater to be treated by general biological methods.The screening of highly efficient degrading bacteria for phenol-containing wastewater has become a research focus in recent years.In this study,m-cresol degrading bacteria GEN05 was taken as the research object.The strain was identified by strain morphological analysis and 16S r RNA sequencing:the colony of the strain was a white translucent pie type with a diameter of 1-2 mm;scanning electron microscopy revealed that the strain was spherical-shaped with a diameter of 0.5-0.6?m.16S r RNA gene sequencing results showed that the strain belongs to C.testosteroni genus and named as Comamonas testosteroni GEN05.The growth curve of the strain was measured,and it was concluded that the strain could enter the logarithmic phase at 16h and reach the stable phase at 56h.By investigating the growth of strains and their ability to degrade m-cresol under different culture conditions,it was concluded that the optimal culture condition is:inoculation amount 5%,p H 7,shaker speed 180 r/min,and temperature 30°C.The degradation concentration range of m-cresol by the strain was further discussed.It was found that m-cresol had an inhibitory effect on the growth of the strain,and the maximum degradation concentration of m-cresol by the strain was 7 m M.The origin software was used to fit the strain growth curve,and it was found that the growth of the strain conformed to the Haldane model.The model parameters were?max=0.82,K_s=218.61mg/L,K_i=87.95mg/L,respectively.Based on the Nanopore sequencing technology platform,the whole genome of strain GEN05 was sequenced,and component analysis,gene function annotation and comparative genomics analysis of the genome were conducted.Seven key genes related to the degradation of m-cresol were found,and the pathway of m-cresol metabolism was speculated.This pathway is meta-metabolism with 3-methylcatechol as a ring-opening substrate.In enzyme activity analysis,phenol hydroxylase and catechol 2,3-dioxygenase were detected.Two intermediate products,3-methylcatechol and 2-hydroxy-2,4-pentadienoic acid,were detected during the degradation of m-cresol by means of LC/MS.The above findings confirmed that the m-cresol metabolic pathway by the strain GEN05 was through the meta-cleavage degradation.