Penicillin-binding proteins (PBPs) are considered essential for bacterial peptidoglycan biosynthesis and cell wall assembly. Clavibacter michiganensis is a representative Gram-positive bacterial species that causes bacterial canker in tomato. pbpC plays a significant role in maintaining cell morphological characteristics and stress responses in C. michiganensis. The current study demonstrated that the deletion of pbpC commonly enhances bacterial pathogenicity in C. michiganensis and revealed the mechanisms through which this occurs. The expression of interrelated virulence genes, including celA, xysA, xysB, and pelA, were significantly upregulated in △pbpC mutants. Compared with those in wild-type strains, exoenzyme activities, the formation of biofilm, and the production of exopolysaccharides (EPS) were significantly increased in △pbpC mutants. It is noteworthy that EPS were responsible for the enhancement in bacterial pathogenicity, with the degree of necrotic tomato stem cankers intensifying with the injection of a gradient of EPS from C. michiganensis. These findings highlight new insights into the role of pbpC affecting bacterial pathogenicity, with an emphasis on EPS, advancing the current understanding of phytopathogenic infection strategies for Gram-positive bacteria.

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Deletion of pbpC Enhances Bacterial Pathogenicity on Tomato by Affecting Biofilm Formation, Exopolysaccharides Production, and Exoenzyme Activities in Clavibacter michiganensis

While confronted with unfavorable growth conditions, bacteria may transform into the dormant state, such as viable but nonculturable (VBNC) state, which is a reversible state characterized by low metabolic activity and lack of division. These dormant cells can be reactivated through the influence of the resuscitation promoting factor (Rpf) family, which are classified as autocrine growth factors and possess peptidoglycan hydrolase activities. To date, with the significant resuscitation or growth promotion ability of Rpf, it has been extensively applied to increasing bacterial diversity and isolating functional microbial species. This review provides a comprehensive analysis of the distribution, mode of action, and functional mechanisms of Rpf proteins in various bacterial species. The aim is to create opportunities for decoding microbial communities and extracting microbial resources from real samples across different research fields. 

Resuscitation Promotion Factor: A Pronounced Bacterial Cytokine in Propelling Bacterial Resuscitation

This review explore the rise of multidrug-resistant (MDR) Gram-negative bacteria, highlighting β-lactamase inhibitor combinations as crucial therapeutic options. It examines β-lactam resistance mechanisms, established combinations (e.g., ticarcillin/clavulanic acid, piperacillin/tazobactam), and the clinical efficacy of newer therapies like ceftazidime/avibactam (CAZ-AVI) for carbapenem-resistant Klebsiella pneumoniae (CRKP) and ceftolozane/tazobactam (TOL-TAZ) for MDR Pseudomonas aeruginosa. Additionally, novel combinations (e.g., cefepime-enmetazobactam, cefepime-taniborbactam) are discussed for tackling extensively drug-resistant (XDR) bacteria. Through comparative analyses, this review provides key insights into efficacy, resistance, pharmacokinetics, and safety, guiding researchers in optimizing antimicrobial strategies and clinicians in managing MDR infections, while supporting antibiotic management and future research. 

Revitalizing cephalosporins: The promise of β-lactamase inhibitor combinations

Mycobacterium tuberculosis, a major cause of mortality from a single infectious agent, possesses a remarkable mycobacterial cell envelope. Penicillin-Binding Proteins (PBPs) are a family of bacterial enzymes involved in the biosynthesis of peptidoglycan. PBP4 (DacB) from M. tuberculosis (MtbPBP4) has been known to function as a carboxypeptidase, and the role and significance of carboxypeptidases as targets for anti-tuberculosis drugs or antibiotics have been extensively investigated over the past decade. However, their precise involvement remains incompletely understood. In this study, we employed predictive modeling and analyzed the three-dimensional structure of MtbPBP4. Interestingly, MtbPBP4 displayed a distinct domain structure compared to its homologs. Docking studies with meropenem verified the presence of active site residues conserved in PBPs. These findings establish a structural foundation for comprehending the molecular function of MtbPBP4 and offer a platform for the exploration of novel antibiotics.

Structural Insights into the Penicillin-Binding Protein 4 (DacB) from Mycobacterium tuberculosis

Peptidoglycan of cell walls in bacteria is a cross-linked and meshlike scaffold that provides strength to withstand the external pressure. The increased cross-linkage in peptidoglycan and altered structure in VBNC cells endowed the cell wall more resistant to adversities. ABSTRACT The cell wall peptidoglycan of bacteria is essential for their survival and shape development. The penicillin-binding proteins (PBPs) are responsible for the terminal stage of peptidoglycan assembly. It has been shown that PBPC, a member of class A high-molecular-weight PBP, played an important role in morphology maintenance and stress response in Clavibacter michiganensis. Here, we reported the stress response strategies under viable but nonculturable (VBNC) state and revealed the regulation of peptidoglycan assembly by PBPC in C. michiganensis cells. Using atomic force microscopy imaging, we found that peptidoglycan of C. michiganensis cells displayed a relatively smooth and dense surface, whereas ΔpbpC was characterized by a “ridge-and-groove” surface, which was more distinctive after Cu2+ treatment. The peptidoglycan layer of wild type cells exhibited a significant increase in thickness and slight increase in cross-linkage following Cu2+ treatment. Compared with wild type, the thickness and cross-linkage of peptidoglycan decreased during log phase in ΔpbpC cells, but the peptidoglycan cross-linkage increased significantly under Cu2+ stress, while the thickness did not change. It is noteworthy that the above changes in the peptidoglycan layer resulted in a significant increase in the accumulation of amylase and exopolysaccharide in ΔpbpC. This study elucidates the role of PBPC in Gram-positive rod-shaped plant pathogenic bacterium in response to environmental stimuli by regulating the assembling of cell wall peptidoglycan, which is significant in understanding the survival of C. michiganensis under stress and the field epidemiology of tomato bacterial canker disease. IMPORTANCE Peptidoglycan of cell walls in bacteria is a cross-linked and meshlike scaffold that provides strength to withstand the external pressure. The increased cross-linkage in peptidoglycan and altered structure in VBNC cells endowed the cell wall more resistant to adversities. Here we systematically evaluated the stress response strategies in Gram-positive rod-shaped bacterium C. michiganensis log phase cells and revealed a significant increase of peptidoglycan thickness and slight increase of cross-linkage after Cu2+ treatment. Most strikingly, knocking-out of PBPC leads to a significant increase in cross-linking of peptidoglycan in response to Cu2+ treatment. Understanding the stress resistance mechanism and survival strategy of phytopathogenic bacteria is the basis of exploring bacterial physiology and disease epidemiology.

Class A Penicillin-Binding Protein C Is Responsible for Stress Response by Regulation of Peptidoglycan Assembly in Clavibacter michiganensis

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Class A Penicillin-Binding Protein C Is Responsible for Stress Response by Regulation of Peptidoglycan Assembly in Clavibacter michiganensis