Toward the elucidation of the advanced mechanism of l-valine production by Corynebacterium glutamicum, a highly developed industrial strain VWB-1 was analyzed, employing. The transcriptional level of 1155 genes and expression abundance of 96 proteins were changed significantly by the transcriptome and proteome comparison of VWB-1 and ATCC 13869. It was indicated that the key genes involved in the biosynthesis of l-valine, ilvBN, ilvC, ilvD , ilvE were up-regulated in VWB-1, which together made prominent contributions in improving the carbon flow towards l-valine. The l-leucine and l-isoleucine synthesis ability were weakened according to the down-regulation of leuB and ilvA. The up-regulation of the branched chain amino acid transporter genes brnFE promoted the l-valine secretion capability of VWB-1. The NADPH and ATP generation ability of VWB-1 were strengthened through the up-regulation of the genes involved in phosphate pentose pathway and TCA pathway. Pyruvate accumulation was achieved through the weakening of the l-lactate, acetate and l-alanine pathways. The up-regulation of the genes coding for elongation factors and ribosomal proteins were beneficial for l-valine synthesis in C. glutamicum. All information acquired were useful for the genome breeding of better industrial l-valine producing valine structure strains.
Corynebacterium glutamicum (C. glutamicum) was isolated in 1957 by Kinoshita and coworkers in a screening program for l-glutamate producing bacteria from a soil sample collected at Ueno Zoo in Tokyo (Japan), it turned out to be a natural producer of L- glutamate under biotin limitation1. The nonpathogenic, GC-rich, Gram-positive bacterium has been used for over 50 years in the industrial production of l-amino acids because of its remarkable ability2. Besides the production of L-glutamate and l-lysine based on a large scale genetically modified high-performance strains3,4, respectively, C. glutamicum is also predominantly used in microorganism for the microbial synthesis of l-valine and other branched-chain amino acids (BCAA) (l-leucine and l-isoleucine)5–7. L-valine is an essential amino acid for vertebrates which is used as a feed additive and is a component of infusion solutions and cosmetics, it is also an important precursor in the chemical synthesis of herbicides8. In order to improve the efficiency of the l-valine production and other products of C. glutamicum, it is important to understand the composition and regulation of the metabolic pathways leading to these industrially important products. Hence, the whole genome sequencing and annotation of the type strain C. glutamicum ATCC 13032 and the wild-type strain C. glutamicum R have deeply influenced the bacterial fermentation performance promotion during the last few years9–11. The genome sequence knowledge also paved the way for the foundation of emerging genome-wide analysis techniques in fields of transcriptomics and proteomics12–15. While previous studies focused on specific genes or enzymes to enhance the l-valine biosynthesis ability of C. glutamicum from the viewpoint of carbon metabolic flux enhancement8,16,17, branched-chain amino acid transportation18 and cofactors supply project19. All those methods have played a certain role in the process of improving the yield of l-valine, however, the regulation of l-valine metabolism in C. glutamicum is a much more complex process. Here we present a global analysis of a high l-valine production C. glutamicum strain by the combination of the two advanced techniques, transcriptional profiling and two-dimensional gel electrophoresis, which allows us to fully understand the deep mechanism of l-valine biosynthesis and other cell growth and metabolism regulation type correlated to it.
