The effect of high concentration isopropanol on the growth of a solvent-tolerant strain of Chlorella vulgaris

The discovery of a highly solvent-tolerant strain of microalga, identified as Chlorella vulgaris by 16S rRNA gene sequencing and termed SDC1 is described here for the first time. Ability to grow in the presence of isopropanol (IPA) solvent was assessed through specific growth rate (A) determination at IPA feed concentrations of up to 16 g 1(-1) at 20 degreesC. Specific growth rates between 0.0017 and 0.0038 h(-1) were obtained in the presence of 2-16 g 1(-1) IPA, and a value of 0.0047 h(-1) evident under IPA-free conditions. Axenic cultures of C vulgaris SDC1 also demonstrated heterotrophic bioconversion of IPA at these elevated concentrations, where acetone, the suggested metabolite, was monitored as an indicator of aerobic degradation of IPA. Comparison of C vulgaris SDC1 growth characteristics was carried out against that of the type culture strain, C vulgaris Beijerinck (CCAP211/11B), where the solvent-tolerant strain SDC1 displayed lower sensitivity to high IPA concentrations. An LD50 value was found to occur at initial IPA concentrations of 3.8 g 1(-1) for the type strain in comparison with 11.25 g 1(-1) for the solvent-tolerant SDC1 strain. Despite several studies discussing the existence of solvent-tolerant bacteria, this is the first time solvent-tolerance at such high IPA concentrations (to 16 g 1(-1)) has been successfully demonstrated by an isolated C vulgaris strain in a mineral salts medium. (C) 2004 Elsevier Inc. All rights reserved.