INCORPORATION OF D-ALANINE INTO LIPOTEICHOIC ACID AND WALL TEICHOIC-ACID IN BACILLUS-SUBTILIS - IDENTIFICATION OF GENES AND REGULATION

The Bacillus subtilis dlt operon (D-alanyl-lipoteichoic acid) is respo nsible for D alanine esterification of both lipoteichoic acid (LTA) an d wall teichoic acid (WTA). The dlt operon contains five genes, dltA-d ltE. Insertional inactivation of dltA-dltD results in complete absence of D-alanine from both LTA and WTA. Based on protein sequence similar ity with the Lactobacillus casei dlt gene products (Heaton, M. P., and Neuhaus, F. C. (1992) J. Bacteriol. 174, 4707-4717), we propose that dltA encodes the D-alanine-n-alanyl carrier protein ligase (Dcl) and d ltC the D-alanyl carrier protein (Dcp). We further hypothesize that th e products of dltB and dltD are concerned with the transport of activa ted n-alanine through the membrane and the final incorporation of D-al anine into LTA. The hydropathy profiles of the dltB and dltD gene prod ucts suggest a transmembrane location for the former and an amino-term inal signal peptide for the latter. The incorporation of D-alanine int o LTA and WTA did not separate in any of the mutants studied which ind icates that either one and the same enzyme is responsible for D-alanin e incorporation into both polymers or a separate enzyme, encoded outsi de the dlt operon, transfers the D-alanyl residues from LTA to WTA (Ha as, R., Koch, H.-U., and Fischer, W. (1984) FEMS Microbiol Lett. 21, 2 7-31). Inactivation of dltE has no effect on D-alanine eater content o f both LTA and WTA and at present we cannot propose any function for i ts gene product. Transcription analysis shows that the dlt operon is t ranscribed from a sigma(D)-dependent promoter and follows the pattern of transcription of genes belonging to the sigma(D) regulon. However, the turn off of transcription observed before sporulation starts seems to be dependent on the SpoOA and AbrB sporulation proteins and result s in a D-alanine-free purely anionic LTA in the spore membrane. The dl t operon is dispensable for cell growth; its inactivation does not aff ect cell growth or morphology as described for L. casei.