Wide variation in the cyanobacterial complement of presumptive penicillin-binding proteins

Abstract

A genomic analysis of putative penicillin-binding proteins (PBPs) that are involved in the synthesis of the peptidoglycan layer of the cell wall and are encoded in 12 cyanobacterial genomes was performed in order to help elucidate the role(s) of these proteins in peptidoglycan synthesis, especially during cyanobacterial cellular differentiation. The analysis suggested that the minimum set of PBPs needed to assemble the peptidoglycan layer in cyanobacteria probably does not exceed one bifunctional transpeptidase-transglycosylase Class A high-molecular-weight PBP; two Class B high-molecular-weight PBPs, one of them probably involved in cellular elongation and the other in septum formation; and one low-molecular-weight PBP. The low-molecular-weight PBPs of all of the cyanobacteria analyzed are putative endopeptidases and are encoded by fewer genes than in Escherichia coli. We show that in Anabaena sp. strain PCC 7120, predicted proteins All2981 and Alr4579, like Alr5101, are Class A high-molecular-weight PBPs that are required for the functional differentiation of aerobically diazotrophic heterocysts, indicating that some members of this class of PBPs are required specifically for cellular developmental processes.

Inhibition of Cell Division Suppresses Heterocyst Development in Anabaena sp. Strain PCC 7120

“…The results obtained showed that although cell growth was severely affected under such conditions, heterocyst formation could still occur, although it was delayed by 1 or 2 days. These results are consistent with the possible involvement of two PBP complexes required for cell elongation and septation, respectively (9,27). In contrast, in a strain overexpressing sulA or inhibited by aztreonam, no heterocyst differentiation was found, even after 4 days.…”

“…6C and D) and indicated that the failure of cell differentiation in a strain overexpressing sulA was independent of the formation of FtsZ ring, but rather the result of the blockage of cell division. We have also used the antibiotic cefsulodin, which inhibits penicillin-binding proteins 1a and 1b (9,27). At a concentration of 30 or 50 g/ml, the growth of the culture was severely inhibited, but no cell elongation was found.…”

Mutations in Four Regulatory Genes Have Interrelated Effects on Heterocyst Maturation in Anabaena sp. Strain PCC 7120

“…strain PCC 7120 as of 2 h of temperature downshift (15). (ii) In our near-saturation transposon mutagenesis experiments (16,17,33,41), the locus of transposition in only one of 1,076 Fox Ϫ transposon mutations (i.e., mutants unable to fix dinitrogen in the presence of oxygen) was localized to the Pol island, a frequency consistent with the frequency of false-positive mutants observed (Fan et al, unpublished observations).…”

“…Nineteen of the 26 presumptive GT ORFs are part of the Hep and Pol expression islands and of the ORF groups all4420 through all4428 and all5221 through all5247. Because restructuring of the vegetative cell wall appears to be required for correct Hep formation (33,41,68,73), it is unclear in which kind of cell, heterocysts or vegetative cells, differentially regulated genes related to envelope synthesis normally function.…”

Identification of Ten Anabaena sp. Genes That under Aerobic Conditions Are Required for Growth on Dinitrogen but Not for Growth on Fixed Nitrogen

“…Additionally, if the estimate is correct that Anabaena sp. has approximately 100 to 140 Fox genes (38), the majority of Fox genes have been discovered, many of them by our transposon mutagenesis screen (10,11,13,17,19,37,40).…”