Abstract
To obtain a yeast mutant with high RNA content and high growth rate, Saccharomyces cerevisiae MTY62 was mutated with ethylmethane sulfonate. Among the selected mutants that were sensitive to the high concentration of KCl, M40-10 strain was finally selected due to its rapid cell growth and high RNA content in the tube and baffled-flask cultures. In the batch culture of M40-10 mutant, the maximum specific growth rate ($\mu_{max}$) of $0.38 h^{-1}$ , RNA concentration of 3210 mg-RNA/1, and RNA content of 183 mg-RNA/g-DCW were obtained, which were 23%, 15%, and 12% increased levels, respectively, compared to those of MTY62 parent strain. The intermittent fed-batch culture of M40-10 strain resulted in the maximum cell concentration of 35.6 g-DCW/1, RNA concentration of 5677 mg/1, and RNA content of 160 mg-RNA/g-DCW. Through the constant fed-batch culture, the maximum cell concentration of 46.4 g-DCW/1, RNA concentration of 6270 mg-RNA/1, and RNA content of 135 mg-RNA/g-DCW were obtained. At the 20 h culture time in the fed-batch cultures of M40-10 strain, the cell and RNA concentrations were increased by 30% and 10%, respectively, over the parent strain MTY62. In addition, it was also found that the accumulated RNA within the mutant cell was not degraded until the end of fed-batch cultivation, indicating that the M40-10 cell is a mutant with weak acidic RNase activity.y.
RNA 함량이 증가되고, 증식속도가 더 빠른 효모 변이주를 선별하기 위해, 모균주 Saccharomyces cerevisiae MTY62 세포에 화학적 돌연변이제인 ethylmethane sulfonate를 처리하여, YPD 배지에서는 잘 자라고 KCl 함유 배지에서는 자라지 않는 변이주들을 선별하였다. 이 변이주들 중 시험관 및 플라스크 배양을 통해 균체농도와 RNA 함량이 모균주 MTY62에 비해 각각 1.5배, 1.3배 증가한 M40-10 변이주를 최종적으로 선별하였다. 변이주 M40-l0을 발효조 회분배양한 결과, 최대비증식속도는 $0.38 h^{-1}$ , RNA 농도는 3210 mg-RNA/1, RNA 함량은 183mg-RNA/g-DCW 값을 보여, 모균주에 비해 각각 23%, 15%, 12%씩 증가하였다. M40-10 변이주를 간헐적 유가배양한 결과, 최대 균체농도는 35.6 g-DCW/1을, 최대 RNA 농도는 5677mg-RNA/l을, RNA함량은 160 mg-RNA/g-DCW을 나타내어 모균주보다 우수하였다. 일정속도의 유가배양에서도 M40-10 변이주의 최대 균체농도는 46.4g-DCW/1, RNA 농도는 6270mg-RNA/1, RNA 함량은 135mg-RNA/g-DCW을 보였다. 이들 유가배양에서 배양 중반기인 20시간 전후에서는 모균주에 비해 변이주의 세포농도는 30%, RNA 농도는 10% 정도 증가되었다. 또한 유가배양 말기까지도 RNA 분해는 거의 일어나지 않아, M40-10 변이주는 산성 RNase 활성이 크게 감소한 변이주임을 알 수 있었다.
