Optimization of heterotrophic culture conditions for n-alkane utilization and phylogenetic position based on the 18S rDNA sequence of a thermotolerant Prototheca zopfii strain

Abstract

This study reports on the optimization of the culture conditions for a thermotolerant eukaryotic algal strain, Prototheca zopfii RND16, which can effectively degrade and assimilate n-alkanes at elevated temperatures. RND16 was able to grow on 1% (v/v) n-alkanes (C 14–C 17) at temperatures up to 38°C. This ability differs from a previous finding that P. zopfii did not grow on hydrocarbons under temperature conditions above 25°C. Increasing the temperature from 25°C to 30–35°C resulted in an increase in the rate of n-alkanes consumption during growth of RND16 in quiescent culture. In shaking culture at 35°C, RND16 removed a 1% n-alkanes mixture almost completely at the basal medium salinity within 8 d. However, an appreciable decrease in the extent of hydrocarbon utilization was observed with increasing salinity and substrate concentration in the medium. The slow consumption of the n-alkanes in the early stage of degradation at 25°C was improved by supplementing 0.1% glucose. A comparative study on the nuclear small subunit rDNA (18S rDNA) sequences of three strains within the genus Prototheca revealed that both P. zopfii ATCC 30253, which utilize n-alkanes at room temperature and P. moriformis ATCC 50081, which does not assimilate n-alkanes, are closely related to RND16.