title: Adaptation and transcriptome analysis of Aureobasidium pullulans in corncob hydrolysate for increased inhibitor tolerance to malic acid production.
abstract: Malic acid is a dicarboxylic acid widely used in the food industry, and is also a potential C4 platform chemical. Corncob is a low-cost renewable feedstock from agricultural industry. However, side-reaction products (furfural, 5-hydroxymethylfurfural (HMF), formic acid, and acetic acid) that severely hinder fermentation are formed during corncob pretreatment. The process for producing malic acid from a hydrolysate of corncob was investigated with a polymalic acid (PMA)-producing Aureobasidium pullulans strain. Under the optimal hydrolysate sugar concentration 110 g/L, A. pullulans was further adapted in an aerobic fibrous bed bioreactor (AFBB) by gradually increasing the sugar concentration of hydrolysate. After nine batches of fermentation, the production and productivity of malic acid reached 38.6 g/L and 0.4 g/L h, respectively, which was higher than that in the first batch (27.6 g/L and 0.29 g/L h, respectively). The adapted strain could grow under the stress of 0.5 g/L furfural, 3 g/L HMF, 2g/L acetic acid, and 0.5 g/L formic acid, whereas the wild type did not. Transcriptome analysis revealed that the differentially expressed genes were related to carbohydrate transport and metabolism, lipid transport and metabolism, signal transduction mechanism, redox metabolism, and energy production and conversion under 0.5 g/L furfural and 3 g/L HMF stress conditions. In total, 42 genes in the adapted strain were upregulated by 15-fold or more, and qRT-PCR also confirmed that the expression levels of key genes (i.e. SIR, GSS, CYS, and GSR) involved in sulfur assimilation pathway were upregulated by over 10-fold in adapted strain for cellular protection against oxidative stress.
authors: College of Pharmaceutical Sciences, Chongqing Engineering Research Center for Pharmaceutical Process and Quality Control, Southwest University, Chongqing 400715, P.R China; Key Laboratory of Biorheological Science and Technology (Chongqing University), Ministry of Education, Chongqing 400044, P.R China.
authors: Xiang
authors: X
authors: Zou
authors: College of Pharmaceutical Sciences, Chongqing Engineering Research Center for Pharmaceutical Process and Quality Control, Southwest University, Chongqing 400715, P.R China.
authors: Yongkang
authors: Y
authors: Wang
authors: College of Pharmaceutical Sciences, Chongqing Engineering Research Center for Pharmaceutical Process and Quality Control, Southwest University, Chongqing 400715, P.R China.
authors: Guangwei
authors: G
authors: Tu
authors: College of Pharmaceutical Sciences, Chongqing Engineering Research Center for Pharmaceutical Process and Quality Control, Southwest University, Chongqing 400715, P.R China.
authors: Zhanquan
authors: Z
authors: Zan
authors: College of Pharmaceutical Sciences, Chongqing Engineering Research Center for Pharmaceutical Process and Quality Control, Southwest University, Chongqing 400715, P.R China.
authors: Xiaoyan
authors: X
authors: Wu
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D001203:Ascomycota / Q000235:genetics* / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D061249:Batch Cell Culture Techniques; D019149:Bioreactors / Q000382:microbiology; D002241:Carbohydrates / Q000032:analysis; D005285:Fermentation / Q000187:drug effects; D005662:Furaldehyde / Q000031:analogs & derivatives / Q000494:pharmacology; D020869:Gene Expression Profiling / Q000379:methods*; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D063990:Gene Ontology; D023281:Genomics; D006868:Hydrolysis; D008293:Malates / Q000378:metabolism*; D009584:Nitrogen / Q000494:pharmacology; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics; D003313:Zea mays / Q000378:metabolism*
chemical_list: D002241:Carbohydrates; D008293:Malates; C008046:5-hydroxymethylfurfural; C030298:malic acid; D005662:Furaldehyde; D009584:Nitrogen