Effect And Mechanism Of Degradation Of Pyridine By Rhodococcus Sp.PDX01 In The Condition Of High Sulfate Concentration

Pyridine is an important precursor to the synthesis of nitrogen heterocyclic pesticides.Because of the existence of solitary pair electrons in the nitrogen atoms on the ring,the density of electron cloud is not concentrated,so the pyridine ring is difficult to crack.The concentration of pyridine in pesticide wastewater can reach6000 mg/L and the sulfate concentration is between 10-25 g/L,which makes it difficult to degrade pyridine by conventional microorganisms.Therefore,this paper studies the degradation of pyridine by Rhodococcus sp.PDX01,a high efficiency pyridine degrading bacteria,which was obtained in the early stage of the research group.The influencing factors of PDX01 degradation of pyridine under high sulfate conditions are discussed.By means of SEM,TEM,EPS determination,UV full wave scanning,FTIR and other means,as well as the analysis of key enzyme activities and compatible solutes,the mechanism of sulfate effect on the degradation of pyridine by PDX01 was analyzed from both extracellular and intracellular aspects.The main conclusions are as follows:(1)The pH and temperature range of PDX01 were 6-10 and 22-42?respectively.The maximum tolerance of Na Cl and Na₂SO₄ was 40 g/L and 100 g/L respectively.The strain has good adaptability to environment and has practical application potential.(2)When the temperature is 42?,the initial pH is 8.0 and the concentration of Na₂SO₄ is less than 100g/L,PDX01 can degrade 1000 mg/L pyridine completely in the simulated wastewater within 72 hours,and the final mineralization rate is stable at87-90%.In addition,PDX01 can degrade 3000 mg/L pyridine in the actual pesticide wastewater by 50%in 10 days.(3)The mechanism of extracellular salt tolerance of PDX01 may be achieved by changing the ratio of protein to polysaccharide in EPS,and maintaining relatively high protein assisted substance transport,rather than producing more EPS;In the high concentration Na₂SO₄ environment,the morphology of PDX01 was not significantly different,the appearance was intact without any sign of rupture,the nitrogen bacteria showed an increasing trend,the membrane secreted from the outside decreased gradually and the surface tended to be smooth;In addition,Na₂SO₄ did not participate in the degradation process of pyridine and did not change the degradation path of pyridine by PDX01.(4)The mechanism of salt tolerance in PDX01 cell may be the way of synthesizing compatibility solute betaine to resist the adverse effect of high salt on osmotic pressure;Under the condition of Na₂SO₄ salt of 80 g/L,the concentration of betaine in PDX01 cell increased from 62.6mg/L to 123.1 mg/L,which may be through accumulation of more proteins near the cell membrane to transport the precursor material to synthesize betaine,and then synthesize in the cell,which is consistent with maintaining high protein concentration outside the cell;The cell structure of the bacteria was clear and complete,but there were many organelles that could be used for the storage of betaine.In addition,the glutaraldehyde dehydrogenase and succinate half aldehyde dehydrogenase,the key enzymes of pyridine degradation,were detected.Na₂SO₄ could affect the activity of extracellular glutaraldehyde dehydrogenase in PDX01,which delayed the degradation of pyridine.