Stress response and tolerance mechanisms of NaHCO3 exposure based on biochemical assays and multi-omics approach in the liver of crucian carp (Carassius auratus).

The development and utilization of saline-alkaline water, an important backup resource, has received widespread attention. However, the underuse of saline-alkaline water, threatened by the single species of saline-alkaline aquaculture, seriously affects the development of the fishery economy. In this work, a 30-day NaHCO3 stress experimental study combined with analyses of untargeted metabolomics, transcriptome, and biochemical approaches was conducted on crucian carp to provide a better understanding of the saline-alkaline stress response mechanism in freshwater fish. This work revealed the relationships among the biochemical parameters, endogenous differentially expressed metabolites (DEMs), and differentially expressed genes (DEGs) in the crucian carp livers. The biochemical analysis showed that NaHCO3 exposure changed the levels of several physiological parameters associated with the liver, including antioxidant enzymes (SOD, CAT, GSH-Px), MDA, AKP, and CPS. According to the metabolomics study, 90 DEMs are involved in various metabolic pathways such as ketone synthesis and degradation metabolism, glycerophospholipid metabolism, arachidonic acid metabolism, and linoleic acid metabolism. In addition, transcriptomics data analysis showed that a total of 301 DEGs were screened between the control group and the high NaHCO3 concentration group, of which 129 up-regulated genes and 172 down-regulated genes. Overall, NaHCO3 exposure could cause lipid metabolism disorders and induce energy metabolism imbalance in the crucian carp liver. Simultaneously, crucian carp might regulate its saline-alkaline resistance mechanism by enhancing the synthesis of glycerophospholipid metabolism, ketone bodies, and degradation metabolism, at the same time increasing the vitality of antioxidant enzymes (SOD, CAT, GSH-Px) and nonspecific immune enzyme (AKP). Herein, all results will provide new insights into the molecular mechanisms underlying the stress responses and tolerance to saline-alkaline exposure in crucian carp.

The characterization of transaldolase gene tal from Pichia stipitis and its heterologous expression in Fusarium oxysporum.

The 972 bp length of transaldolase gene tal was cloned from Pichia stipitis CICC1960, encoding a 323 amino acid protein with a calculated molecular mass of 35.36 kDa and isoelectric point of 5.20. Real time PCR analysis demonstrated that the mRNA transcript level of constitutive tal gene rise on xylose, glucose, fructose, mannose, galactose and sucrose as carbon source, respectively. Furthermore, the transcription of tal gene in P. stipitis on xylose was higher than on other carbon source, indicating that transaldolase plays a part in xylose utilization. To deeply study the tal gene biological function, it was expressed in Fusarium oxysporum CCTCC M209040. Recombinant transaldolase activity of transformant F. oxysporum M209040-Tal2 was about 0.52 U mg(-1) protein and was 1.57 times higher than that of the wild type F. oxysporum CCTCC M209040, indicating that the improvement of transaldolase activity in transformant was due to expression of the exogenous tal gene. Growth of transformant F. oxysporum M209040-Tal2 without selection pressure did not affect the level of hygromycin resistance of the transformants, suggesting that integrated tal gene was stable in mitosis. Fermentation trials of F. oxysporum M209040-Tal2 showed that the ethanol yield improved by 8.39 and 11.71% on glucose and xylose substrates, respectively, demonstrating that the expression of tal gene from P. stipitis CICC1960 in F. oxysporum CCTCC M209040 could improve ethanol production.