두공생 세균에 의한 PVA 분해 최적조건 및 고온성 PVA 분해 변이주 선별에 관한 연구

The optimal conditions for polyvinyl alcohol(PVA) utilization by the two symbiotic isolates, Pasteurella haemolytica KMG 1 and Pseudomonas sp. KMG5 were investigated. Maximum PVA utilization occurred at pH 8.0 and 37℃ after culturing for 6 days in the minimal medium containing 0.75% PVA as a sole carbon and energy source. In the mixed culture, the KMG5 strain that had previously been proved to be the actual PVA degrader constituted the predominant population. The symbiont strains utilized equally well all types of PVA substrates irrespective of their polymerization degrees(500-30,000). The presence of additional carbon sources such as glucose, galactose, glycerol and ethanol did not affect the PVA utilizing activity of the mixed culture. On the other hand, maltose and sucrose severely inhibited the cell growth, leading to the great reduction of the level of PVA degradation. All nitrogen sources examined except urea, corn steep liquor and skim milk increased similarly and markedly the PVA degrading activity of the symbiotic culture. The growth of KMGS, one of the two symbionts was observed to be inhibited at the high temperatures above 37℃. Hence, in this study we also isolated a thermophilic mutant (KMG6) from the KMG5 cells, which enabled the mixed culture of KMG1 and KMG6 to degrade PVA effectively at 40℃.