Abstract
Chlamydiales species are obligate intracellular bacteria lacking a classical peptidoglycan sacculus but relying on peptidoglycan synthesis for cytokinesis. While septal peptidoglycan biosynthesis seems to be regulated by MreB actin and its membrane anchor RodZ rather than FtsZ tubulin in Chlamydiales, the mechanism of peptidoglycan remodeling is poorly understood. An amidase conserved in Chlamydiales is able to cleave peptide stems in peptidoglycan, but it is not clear how peptidoglycan glycan strands are cleaved since no classical lytic transglycosylase is encoded in chlamydial genomes. However, a protein containing a SpoIID domain, known to possess transglycosylase activity in Bacillus subtilis, is conserved in Chlamydiales We show here that the SpoIID homologue of the Chlamydia-related pathogen Waddlia chondrophila is a septal peptidoglycan-binding protein. Moreover, we demonstrate that SpoIID acts as a lytic transglycosylase on peptidoglycan and as a muramidase on denuded glycan strands in vitro As SpoIID-like proteins are widespread in nonsporulating bacteria, SpoIID might commonly be a septal peptidoglycan remodeling protein in bacteria, including obligate intracellular pathogens, and thus might represent a promising drug target.IMPORTANCEChlamydiales species are obligate intracellular bacteria and important human pathogens that have a minimal division machinery lacking the proteins that are essential for bacterial division in other species, such as FtsZ. Chlamydial division requires synthesis of peptidoglycan, which forms a ring at the division septum and is rapidly turned over. However, little is known of peptidoglycan degradation, because many peptidoglycan-degrading enzymes are not encoded by chlamydial genomes. Here we show that an homologue of SpoIID, a peptidoglycan-degrading enzyme involved in sporulation of bacteria such as Bacillus subtilis, is expressed in Chlamydiales, localizes at the division septum, and degrades peptidoglycan in vitro, indicating that SpoIID is not only involved in sporulation but also likely implicated in division of some bacteria.
Highlights
Chlamydiales species are obligate intracellular bacteria lacking a classical peptidoglycan sacculus but relying on peptidoglycan synthesis for cytokinesis
SpoIID of B. subtilis has been well studied and was shown previously to be a lytic transglycosylase required for PG remodeling during sporulation of this bacterium [18]
The SpoIID protein was detected as a PG-binding protein in a screen that we performed to investigate W. chondrophila proteins cosedimenting with PG
Summary
Chlamydiales species are obligate intracellular bacteria lacking a classical peptidoglycan sacculus but relying on peptidoglycan synthesis for cytokinesis. An amidase conserved in Chlamydiales is able to cleave peptide stems in peptidoglycan, but it is not clear how peptidoglycan glycan strands are cleaved since no classical lytic transglycosylase is encoded in chlamydial genomes. Chlamydiales underwent a drastic genome reduction apparently driven by the adaptation of these bacteria to an intracellular parasitic lifestyle [6,7,8] but still retained all minimal determinants required for cell division and to synthesize and remodel PG. Amidases able to cleave peptide stems at the amide bond of MurNAc were described in Waddlia chondrophila and Chlamydia pneumoniae [15, 16], but chlamydial genomes do not code for homologues of classical lytic transglycosylases [17], raising the issue of how the glycan strand is cleaved. Since a SpoIIDdomain containing protein of Bacillus subtilis was demonstrated previously to be a lytic transglycosylase involved in sporulation [18, 19], this activity might be conserved in Chlamydiales
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