Abstract
The growth and cultural characteristics of Bacillus sp. SH-8 and SH-8M were investigated at various pH conditions. Bacillus sp. SH-8 showed normal growth pattern above pH 9.0. However, with the pH adjusted below 7.7, 0.$D_{550}$ decreased rapidly with concomitant reduction in viable cell numbers. In contrast, Bacillus sp. SH-8M demonstrated growth capability at pH 7.7, but with slightly reduced growth rate at pH 6.9. Similar results were obtained when those two strains were cultivated on the solid medium. Both of them showed short rod shapes at pH 10.2. However, at pH 7.7 only Bacillus sp. SH-8 was observed to have elongated rod shape. Extracellular pH of both the strains, when cultured at initial pH of 10.2, reached to 9.0 after the incubation of 28 hours. At the initial pH of 9.0 and 9.6, the extracellular pH was reduced at the beginning of cultivation, but elevated after 12 hours. When cultured at initial pH of 6.9 and 7.7, extracelluar pH of Bacillus sp. SH-8M increased to 8.0 and 8.7, respectively, while that of Bacillus sp. SH8 remained constant pH 7.0. The highest sporulation rate of Bacillus sp. SH-8 and SH-8M was obtained at the initial pH of 10.2 and after the incubation of 3 days with the sporulation rate of 95% and 85%, respectively.
Bacillus sp. SH-8은 pH 9.0 이상에서 생육이 가능하였고 pH 7.7 이하에서는 배양 12시간부터 O.$D_{550}$가 급격히 감소하였으며 생균수도 감소하였다. 그러나 Bacillus sp. SH-8M은 pH7.7에서 생육이 가능하였고 pH6.9에서도 약간 생육속도가 늦었으나 정상적인 생육을 나타내었다. 고체배지의 생육 양상도 액체배지에서와 비슷한 결과를 나타내었다. 균주의 형태는 pH 10.2에서 두 균주 모두 단간균위 형태를 나타내었으나 pH7.7에서는 Bacillus sp. SH-8 균주만이 장간균의 형태를 나타내었다. 균체외 pH는 초기 10.2일 때 두 균주 모두 배양 28시간 후에는 9.0이었고 초기 pH 9.0와 9.6에서는 배양초기에 pH가 저하되었다가 12시간 후부터 상승하였다. 한편, Bacillus sp. SH-8M은 초기 pH 6.9와 7.7일때 배양시간에 따라 균체외의 pH가 8.0과 8.7로 상승하였으나 Bacillus sp. SH-8은 배양 12시간 이후에도 7.0으로 일정하였다. 포자형성능은 Bacillus sp. SH-8과 Bacillus sp. SH-8M 모두 배양 3일 후, 초기 pH 10.2일 때 각각 95%와 85%로 가장 높았다.