Transcriptional regulation of fatty acid biosynthesis in Streptococcus pneumoniae

The transcriptional regulation of membrane fatty acid composition in the human pathogen Streptococcus pneumoniae is distinct from the systems utilized in the model organisms Escherichia coli and Bacillus subtilis. The genes encoding the components of type II fatty acid biosynthesis cluster at a single location within the S. pneumoniae genome, and the second gene in this cluster (SPR0376) encodes a transcription factor (FabT) that belongs to the MarR superfamily. Derivatives of S. pneumoniae strain D39 were constructed that lacked functional FabT. This strain had significantly elevated levels of saturated fatty acids and longer chain lengths than the control strain, was unable to grow at pH 5.5 and had increased sensitivity to detergent. Eliminating FabT function increased the expression levels of all of fab genes with the notable exception of fabM. FabT was purified and bound to the DNA palindrome located within the promoter regions of the fabT and fabK genes within the cluster. The analysis of cells with increased expression of individual genes leads to a model where the physical properties of the S. pneumoniae membrane is controlled primarily by the activity of FabK, the enoyl reductase, which diverts intermediates to saturated fatty acid formation, in contrast to E. coli where FabB, an elongation condensing enzyme, pulls the pathway in the direction of unsaturated acid synthesis.