Study On The Tolerance Of Trichosporon Cutaneum To Phenolic Compounds And Its Microbial Lipid Production From Lignocellulosic Feedstock

Pretreatment is the key step to destroy the dense structure of lignocellulose and promote the subsequent enzymatic hydrolysis.However,microorganisms are generally hard to survive in lignocellulose system due to the presence of inhibitors generated from the lignocellulose pretreatment,so the detoxification step is always followed to remove the inhibitors.Biodetoxification have great advantages on the removal of inhibitors,which can selectively remove weak organic acids and furan aldehydes inhibitors without causing the loss of fermentable sugars;However,biodetoxification has a low efficiency in removing phenolic inhibitors.Previous results show that many oleaginous yeasts are difficult to survive in lignocellulosic feedstock,even the raw materials have been deeply detoxified by biodetoxification.This study firstly investigated the cell growth and metabolism of various oleaginous yeasts in the pretreated and biodetoxified lignocellulosic feedstock.It is suspected that the existence of residual phenolic aldehydes is responsible for the poor viability of oleaginous yeasts.While cultured in the synthetic medium containing only phenolic aldehydes inhibitors and wheat straw hydrolysate,Rhodosporidium toruloides,Rhodotorula glutinis,Yarrowia lipolytica are generally hard to survive;the cell growth and lipid accumulation of T.cutaneum ACCC 20271,T.cutaneum MP11 were also significantly affected.These results confirmed that the existence of residual phenolic aldehydes was the major reason for poor cell growth and metabolism of oleaginous yeasts in lignocellulosic feedstock.Secondly,the bioconversion of phenolic aldehydes by the above 5 strains of yeast was investigated.T.cutaneum ACCC 20271 and T.cutaneum MP11 almost completely converted 4-hydroxybenzaldehyde(HBA),vanillin or syringaldehyde into their alcohols and acids form,then alcohol or acid were also effectively degraded;on the other hand,the other three yeasts can only convert a small amount of 4-hydroxybenzaldehyde,vanillin or syringaldehyde into alcohol and acid derivatives,and the acid can't be further degraded.Finally,simultaneous saccharification and lipid co-fermentation was carried out using wheat straw under high solid content,T.cutaneum showed satisfactory lipid accumulation in the actual system(40.87±1.85 g/L).These results provide an important theoretical basis for the application of T.cutaneum to the lipid production from lignocellulose.In addition,the utilization of acetic acid and levulinic acid by T.cutaneum,which were main weak organic acids inhibitors from lignocellulose,was also investigated.By using acetic acid and levulinic acid as carbon sources for fed-batch fermentation,T.cutaneum MP11 can use acetic acid and levulinic acid for cell growth and lipid accumulation.This study provides a theoretical support for the utilization of unconventional carbon sources from lignocellulose.