Most bacteria possess a peptidoglycan cell wall that determines their morphology and provides mechanical robustness during osmotic challenges. The biosynthesis of this structure is achieved by a large set of synthetic and lytic enzymes with varying substrate specificities. Although the biochemical functions of these proteins are conserved and well-investigated, the precise roles of individual factors and the regulatory mechanisms coordinating their activities in time and space remain incompletely understood. Here, we comprehensively analyze the autolytic machinery of the alphaproteobacterial model organism Caulobacter crescentus, with a specific focus on LytM-like endopeptidases, soluble transglycosylases, and amidases. Our data reveal a high degree of redundancy within each protein family but also specialized functions for individual family members under stress conditions. In addition, we identify two lytic transglycosylases and an amidase as new divisome components that are recruited to midcell at distinct stages of the cell cycle. The midcell localization of these proteins is affected by two LytM factors with degenerate catalytic domains, DipM and LdpF, which may serve as regulatory hubs coordinating the activities of multiple autolytic enzymes during cell constriction and fission, respectively. These findings set the stage for in-depth studies of the molecular mechanisms that control peptidoglycan remodeling in C. crescentus.This article is protected by copyright. All rights reserved.3

During growth, microorganisms have to balance metabolic flux between energy and biosynthesis. One of the key intermediates in central carbon metabolism is acetyl coenzyme A (acetyl-CoA), which can be either oxidized in the citric acid cycle or assimilated into biomass through dedicated pathways. Two acetyl-CoA assimilation strategies in bacteria have been described so far, the ethylmalonyl-CoA pathway (EMCP) and the glyoxylate cycle (GC). Here, we show that Paracoccus denitrificans uses both strategies for acetyl-CoA assimilation during different growth stages, revealing an unexpected metabolic complexity in the organism’s central carbon metabolism. The EMCP is constitutively expressed on various substrates and leads to high biomass yields on substrates requiring acetyl-CoA assimilation, such as acetate, while the GC is specifically induced on these substrates, enabling high growth rates. Even though each acetyl-CoA assimilation strategy alone confers a distinct growth advantage, P. denitrificans recruits both to adapt to changing environmental conditions, such as a switch from succinate to acetate. Time-resolved single-cell experiments show that during this switch, expression of the EMCP and GC is highly coordinated, indicating fine-tuned genetic programming. The dynamic metabolic rewiring of acetyl-CoA assimilation is an evolutionary innovation by P. denitrificans that allows this organism to respond in a highly flexible manner to changes in the nature and availability of the carbon source to meet the physiological needs of the cell, representing a new phenomenon in central carbon metabolism. IMPORTANCE Central carbon metabolism provides organisms with energy and cellular building blocks during growth and is considered the invariable “operating system” of the cell. Here, we describe a new phenomenon in bacterial central carbon metabolism. In contrast to many other bacteria that employ only one pathway for the conversion of the central metabolite acetyl-CoA, Paracoccus denitrificans possesses two different acetyl-CoA assimilation pathways. These two pathways are dynamically recruited during different stages of growth, which allows P. denitrificans to achieve both high biomass yield and high growth rates under changing environmental conditions. Overall, this dynamic rewiring of central carbon metabolism in P. denitrificans represents a new strategy compared to those of other organisms employing only one acetyl-CoA assimilation pathway.