Enhanced Bacterial Growth and Gene Expression of D-Amino Acid Dehydrogenase With D-Glutamate as the Sole Carbon Source

• Published in: Frontiers in microbiology 2018-09, Vol.9, p.2097-2097
• Main Authors: Naganuma, Takeshi, Iinuma, Yoshiakira, Nishiwaki, Hitomi, Murase, Ryota, Masaki, Kazuo, Nakai, Ryosuke
• Format: Article
• Language: English
• Subjects: D-amino acid dehydrogenase; D-glutamate; dadA; gene expression; Microbiology; Pseudomonas aeruginosa; Raoultella ornithinolytica
• ISSN: 1664-302X; 1664-302X
• DOI: 10.3389/fmicb.2018.02097

In a search for life-supporting, not life-assisting, D-amino acid metabolism, an environmental strain that grows better with D-glutamate as the sole carbon source was isolated from an ordinary river. The strain, designated as A25, exhibited a faster growth rate and greater cell yield with D-glutamate than with L-glutamate. Conversely, the D/L ratio of total cellular glutamate was as low as 4/96, which suggests that D-glutamate is more likely catabolized than anabolized. Strain A25 was phylogenetically most closely related to the gamma-proteobacterial species , with a 16S rRNA gene sequence similarity of 100%. A standard strain, JCM 6096 , also showed similarly enhanced growth with D-glutamate, which was proven for the first time. Gene expression of the enzymes involved in D-amino acid metabolism was assayed by reverse-transcription quantitative PCR (RT-qPCR) using specifically designed primers. The targets were the genes encoding D-amino acid dehydrogenase (DAD; EC 1.4.99.1), glutamate racemase (EC 5.1.1.3), D-glutamate oxidase (EC 1.4.3.7 or EC 1.4.3.15), and UDP-N-acetyl-α-D-muramoyl-L-alanyl-D-glutamate ligase (EC 6.3.2.9). As a result, the growth of strains A25 and JCM 6096 on D-glutamate was conspicuously associated with the enhanced expression of the DAD gene ( ) in the exponential phase compared with the other enzyme genes. is also known to grow on D-glutamate as the sole carbon source but to a lesser degree than with L-glutamate. A standard strain of , JCM 5962 , was tested for gene expression of the relevant enzymes by RT-qPCR and also showed enhanced expression, but in the stationary phase. Reduction of ferricyanide with D-glutamate was detected in cell extracts of the tested strains, implying probable involvement of DAD in the D-glutamate catabolizing activity. DAD-mediated catalysis may have advantages in the one-step production of α-keto acids and non-production of H O over other enzymes such as racemase and D-amino acid oxidase. The physiological and biochemical importance of DAD in D-amino acid metabolism is discussed.