1. Introduction
L-Ornithine is an important chemical ingredient for its applications in food and pharmaceutical industries as a dietary supplement, as it is known to be efficacious in the treatment of liver diseases and wound healing [11]. It can also be used as a precursor for the synthesis of other amino acids, such as arginine and citrulline, and putrescine, an important diamine used as a nylon precursor [28]. L-Ornithine could be produced by fermentation using auxotrophic mutants, for example, citrulline- or arginine-required mutants of Acinetobacter lwoffi and Coryneform bacterium obtained by traditional mutagenesis [1,6,18]. However, the product yield of L-ornithine is low and growth of the auxotrophic mutants is unstable owing to development …show more content…
Recent studies have illustrated that C. glutamicum might be more advantageous as an L-ornithine overproducer [16]. In C. glutamicum, the L-ornithine biosynthetic pathway is cyclic due to L-ornithine acetyltransferase (OATase, encoded by argJ; EC 2.3.1.35), which catalyzes the conversion of N-acetyl-L-ornithine and L-glutamate to L-ornithine and N-acetyl-L-glutamate (NAG). NAG kinase (NAGK, encoded by argB; EC 2.7.2.8) then phosphorylates NAG in the second step of the pathway. Besides OATase and NAGK, argC-encoded N-acetyl-L-glutamate 5-semialdehyde dehydrogenase and argD-encoded N-acetyl-L-ornithine aminotransferase are critical for the conversion of L-glutamate to L-ornithine (As shown in Fig. 1). Actually, these five genes are involved in one of the L-arginine synthesis cluster, named argCJBDF in Corynebacteria strains. However, it has been reported that OATase is only responsible for deacetylation of N-acetylornithine as N-acetyl-L-ornithine deacetylase …show more content…
crenatum (subspecies of C. glutamicum) from a soil sample, and through a series of mutant breeding the mutant strain SYPA 5-5 could produce 30.6 g/L of L-arginine [42]. we firstly attempted to enhance L-ornithine accumulation by deleting the bypass and alleviating the ornithine-inhibition of OATase but recorded low enzyme activity. Thus, for enhance L-ornithine biosynthesis, our next strategy, was to co-express the E. coli’s argA and S. marcescens’s argE in C. crenatum so as to mimic a linear transacetylation pathway. To our knowledge, this is the first reported improved L-ornithine production in C. crenatum by introducing an artificial linear transacetylation
L-Ornithine is an important chemical ingredient for its applications in food and pharmaceutical industries as a dietary supplement, as it is known to be efficacious in the treatment of liver diseases and wound healing [11]. It can also be used as a precursor for the synthesis of other amino acids, such as arginine and citrulline, and putrescine, an important diamine used as a nylon precursor [28]. L-Ornithine could be produced by fermentation using auxotrophic mutants, for example, citrulline- or arginine-required mutants of Acinetobacter lwoffi and Coryneform bacterium obtained by traditional mutagenesis [1,6,18]. However, the product yield of L-ornithine is low and growth of the auxotrophic mutants is unstable owing to development …show more content…
Recent studies have illustrated that C. glutamicum might be more advantageous as an L-ornithine overproducer [16]. In C. glutamicum, the L-ornithine biosynthetic pathway is cyclic due to L-ornithine acetyltransferase (OATase, encoded by argJ; EC 2.3.1.35), which catalyzes the conversion of N-acetyl-L-ornithine and L-glutamate to L-ornithine and N-acetyl-L-glutamate (NAG). NAG kinase (NAGK, encoded by argB; EC 2.7.2.8) then phosphorylates NAG in the second step of the pathway. Besides OATase and NAGK, argC-encoded N-acetyl-L-glutamate 5-semialdehyde dehydrogenase and argD-encoded N-acetyl-L-ornithine aminotransferase are critical for the conversion of L-glutamate to L-ornithine (As shown in Fig. 1). Actually, these five genes are involved in one of the L-arginine synthesis cluster, named argCJBDF in Corynebacteria strains. However, it has been reported that OATase is only responsible for deacetylation of N-acetylornithine as N-acetyl-L-ornithine deacetylase …show more content…
crenatum (subspecies of C. glutamicum) from a soil sample, and through a series of mutant breeding the mutant strain SYPA 5-5 could produce 30.6 g/L of L-arginine [42]. we firstly attempted to enhance L-ornithine accumulation by deleting the bypass and alleviating the ornithine-inhibition of OATase but recorded low enzyme activity. Thus, for enhance L-ornithine biosynthesis, our next strategy, was to co-express the E. coli’s argA and S. marcescens’s argE in C. crenatum so as to mimic a linear transacetylation pathway. To our knowledge, this is the first reported improved L-ornithine production in C. crenatum by introducing an artificial linear transacetylation