Degradation Of Atrazine And Lactic Acid Metabolism In Aureobasidium Pullulans

As a filamentous fungus,Aureobasidium pullulans has a growth stage such as yeast cell,swell cell and chlamydospores,and has the ability to produce pullulan,which is an important organic substance.In this study,we found Aureobasidium pullulans not only secrete a small molecular substance(AP factor)with laccase activity but also produce lactic acid by detecting the NG fermentation broth of Aureobasidium pullulans.Laccase is a copper-containing polyphenol oxidase that contains copper ions with special oxidation-reduction capabilities to catalyze and oxidize various aromatic substrates.lactic acid,as an organic acid,which is also an indispensable industrial compound and plays an important role in the world.In recent years,with the increasing use of poly-lactic acid,the demand for lactic acid has also increased.(1)This study found that the laccase activity of AP factor after dialysis,rotary evaporation and freeze-drying can be increased from 27.96 U/L to 277.78 U/L.The AP factor was co-treated with atrazine at 45°C.The degradation rate of atrazine by high temperature sterilized AP factor was 56.11%,while the degradation rate of atrazine by non-sterilized AP factor was only 29.77.%.(2)It also found that the strains and cell morphology,lactic acid production,biomass,p H and AP factor activity of A.pullulans strains were different under aerobic and micro-aerobic fermentation.The accumulated lactic acid of Aureobasidium pullulans in the cells reached a peak in 72 h(aerobic,13.38 mmol/L)or 120 h(micro-aerobic,4.34 mmol/L),then decreased.The Aureobasidium pullulans secreted lactic acid under aerobic or micro-aerobic conditions.The secreted lactic acid under aerobic conditions reached the highest(2.58 mmol/L)at 24 h,and then gradually decreased by providing the energy to the cells,and remained stable after 96 h.Under micro-aerobic conditions,it was beneficial for the cell to secrete lactic acid.After 72 h fermentation,the yield of lactic acid was 3.46 mmol/L.The above results indicated that the A.pullulans NG can undergo lactic acid fermentation while aerobic metabolism,and lactic acid can accumulate in the cells and secrete to extracellular.It was speculated that lactic acid play an important role in the material and energy metabolism of Aureobasidium pullulans.When the medium carbon source was insufficient,the yeast cells used extracellular lactic acid.Aureobasidium pullulans had a complex lactic acid metabolism mechanism.Seven lactate dehydrogenase genes were found in the transcriptome.The result of real-time quantitative PCR revealed that the transcriptional levels of two lactate dehydrogenase genes comp5964 and comp4988 were positively correlated with lactic acid production.The expression of lactate dehydrogenase under aerobic fermentation was significantly up-regulated compared to the expression of lactate dehydrogenase under micro-aerobic fermentation.The metabolomics analysis showed that in micro-aerobic fermentation,a total of 6825 metabolites changed in positive ion mode,of which 4505 metabolites were significantly up-regulated relative to aerobic fermentation and 2320 metabolites were down-regulated.In negative ion mode,a total of 8028 metabolites changed,of which 5362 metabolites were significantly up-regulated relative to aerobic fermentation,and 2666 metabolites were down-regulated.114 metabolic pathways have changed in micro-aerobic fermentation and enriched four lactate dehydrogenase metabolic pathways,respectively named glycolysis and gluconeogenesis metabolism,cysteine and methionine metabolism,pyruvate metabolism,and propionic acid metabolism,etc.