Functional characterization of the peptidoglycan recycling pathway in Caulobacter crescentus

Most bacteria possess a peptidoglycan (PG) cell wall that is required to withstand the turgor pressure, maintain cell shape and establish a physical barrier against the environment. The PG layer needs to be constantly remodeled to enable the cells to elongate, grow and divide.

During this process, small PG fragments are released into the periplasm. As these fragments can be used as a source for new PG building blocks, many bacteria take great effort in recycling these degradation products. Enterobacteria, such as Escherichia coli, for instance, reuse up to 60 % of released PG fragments. To this end, the turnover products are transported into the cytoplasm and further degraded by a set of PG recycling-specific enzymes, which separate the two sugar moieties and degrade the peptide stem.

While E. coli and other Gammaproteobacteria have rather simple shapes, the class of Alphaproteobacteria shows a variety of different cell shapes. In these organisms, correct PG remodeling and therefore also the availability of PG precursors seems to be even more important to maintain the complex cell shapes. On organism belonging to the Alphaproteobacteria is C. crescentus, a crescent-shaped bacterium that is characterized by a biphasic life cycle involving to morphological distinct cell types and asymmetric cell division.

Here, we identified that C. crescentus also has a functional PG recycling pathway, which is, although not necessary for general growth, essential to maintain proper cell shape. Additionally, we observed that PG recycling is needed to maintain the natural ß-lactam resistance of C. crescentus. By characterizing the so far unknown PG recycling mechanism in Alphaproteobacteria, identifying its relevance for the cells and understanding the connection between ß-lactam resistance and PG recycling, we aim to gain novel insights which can help uncovering potential treatments against pathogenic Alphaproteobacteria such as Bartonella or Brucella species.