| Diatoms, a group of microalgae, are typically photosynthetic and known to produce large amounts of triacylglycerols, which are often composed of commercially valuable fatty acids. Fatty acid biosynthesis and photosynthesis seem to be closely related. Both processes occur in the chloroplast of photosynthetic organisms, involve energy metabolism, and are responsive to cellular stress.; Triacylglycerols were found to accumulate in nitrogen stressed diatoms. To determine whether this response could be useful in maximizing lipid production, fatty acid composition was compared in diatoms grown under a range of nitrogen concentrations. Nitrogen stress resulted in a reduction in the amounts of particularly valuable fatty acids relative to total fatty acid content.; The genomes of the photosynthetic Chaetoceros muelleri and the non-photosynthetic Nitzschia alba were analyzed. Although the genome of N. alba was significantly reduced, N. alba possessed certain plastid specific genes and like photosynthetic diatoms, retained a multi-membrane plastid envelope which would enable import of nuclear encoded genes to the plastid.; The antibiotic thiolactomycin has been shown to specifically inhibit the plastid enzymes of fatty acid biosynthesis. We compared the effect of the antibiotic on the non-photosynthetic diatom N. alba and the closely related photosynthetic diatom, Nitzschia laevis, to determine whether plastid fatty acid biosynthesis occurs in the non-photosynthetic diatom. While the magnitude of effect of the thiolactomycin differed among the two organisms, both were sensitive to the antibiotic. Growth of N. laevis was noticeably affected at a concentration of 400 μM, while growth of N. alba was not. Neutral lipid accumulation and fatty acid biosynthesis were influenced in both organisms at concentrations of 200 and 400 μM, respectively.; The presence of plastid encoded fatty acid biosynthetic proteins, an intact plastid envelope, and sensitivity to thiolactomycin suggest that aside from the loss of photosynthesis, the plastid of N. alba is otherwise biochemically functional. |
