Kazumi Araki

Microbial Production of Essential Amino Acids with Corynebacterium Glutamicum Mutants

Amino acids produced by microbial process are generally L-forms. The stereospecificity of the amino acids produced by fermentation makes the process advantageous compared with synthetic process. Microorganisms employed in microbial process for amino acid production are divided into 4 classes; wild-type strain, auxotrophic mutant, regulatory mutant and auxotrophic regulatory mutant. Using such mutants of Corynebacterium glutamicum, all the essential amino acids but L-methionine are now being produced by direct fermentation from cheap carbon sources such as carbohydrate materials or acetic acid.

Studies on Histidine Fermentation:Part I. L-Histidine Production by Histidine Analog-resistant Mutants from Several Bacteria

Mutants resistant to 1,2,4-triazolealanine (TRA) or 2-thiazolealanine (TA) were derived from Corynebacterium glutamicum ATCC-13761 by mutagenic treatment with N-methyl-N′-nitro-N-nitrosoguanidine. More than eighty percent of these mutants were found to accumulate a large amount of l-histidine in culture broth. Among these histidine producers, KY-10260 which was selected on TRA-containing agar, was used to investigate the cultural conditions for histidine production. The amount of histidine accumulation reached to a level of 6~8 mg/ml with a medium containing 15% molasses (as glucose) and 4.5% ammonium sulfate.According to the similar procedure, some histidine producers were derived from other bacteria, Arthrobacter citreus, Brevibacterium flavum, Bacillus megaterium, Bacillus subtilis and Nocardia globerula.

Selection of Microorganisms Producing L-Serine from Glycine

L-セリン生合成の前駆体であるDL一グJセリン酸10mg/ml,L-スレオニン10mg/mlまたはグリシン5mg/mlを各々添加した3種の培地で,細菌,酵母,放線菌,カビの野生株および変異森,合計1416株を培養し,L-セリンを培地中に蓄積する菌株の選択を行なった.この結果,試験した菌株中にはDL-グジセリン酸,L-スレオニンからは著量のL-セリンを生産する菌株はみいだせなかったが,グリシンからL-セリン約1mg/ml生産する菌株として,炭化水素資化性菌である,Nocardia butanicaATCC 21197,Nocardia paraffinicaATCC 21198,Brevibacterium ketoglutamicumATCC 15587を選択した.また使用菌株の大多数は,培地中に添加したL-セリン5mg/mlを90%以上,グリシン以外の物質に代謝分解したが,上記のL-セリン生産株3株はいずれもL-セリン分解能の弱い(分解能40%以下)6株中に含まれた.またL-スレオニンからα-アミノ酪酸,レイソロイシン,グリシンをそれぞれ生成する菌株もみいだされた.