Effect of aceE gene knockout on pyruvate metabolism of Streptococcus suis

Abstract:

[Objective] To explore the effect of the knockout of aceE gene which encodes pyruvate dehydrogenase on the growth characteristics,tricarboxylic acid cycle,and pyruvate metabolism of Streptococcus suis.[Methods] The growth curves of the wild-type strain and strain ΔaceE were established with the OD₆₀₀ values of the bacterial liquids.The content of acetyl CoA,succinate CoA,fumarate,oxaloacetate,pyruvate,lactate,and ATP in the tricarboxylic acid cycle and the pyruvate metabolism bypass was measured.Quantitative RT-PCR was employed to determine the gene expression levels of citrate synthase,malate dehydrogenase,succinate dehydrogenase,isocitrate dehydrogenase,pyruvate decarboxylase,lactate dehydrogenase,alcohol dehydrogenase,and acetaldehyde dehydrogenase.[Results] Compared with the wild-type strain,strain ΔaceE showed decreasing OD₆₀₀ value during the platform phase.The OD₆₀₀ value of strain ΔaceE in the plateau phase significantly increased after the addition of 1 g/L acetate.Compared with the wild-type strain,strain ΔaceE showed increased content of pyruvate while decreased content of ATP,acetyl CoA,succinate CoA,and fumarate.Moreover,it showed up-regulated expression levels of citrate synthase and malate dehydrogenase,while down-regulated expression levels of succinate dehydrogenase and isocitrate dehydrogenase.For the proteins involved in pyruvate metabolism bypass,pyruvate decarboxylase,lactate dehydrogenase,alcohol dehydrogenase,and acetaldehyde dehydrogenase presented up-regulated gene expression levels in strain ΔaceE.[Conclusion] Strain ΔaceE has reduced activity of tricarboxylic acid cycle.Although part of pyruvate can be decomposed into acetate through the pyruvate dehydrogenease bypass and further converted into acetyl CoA to enter the tricarboxylic acid cycle,the ATP content has not been restored to the wild-type strain level.This study provides a theoretical basis for further research on the relationship between metabolic changes and bacterial phenotypes.