Research Projects

The bacterial cell wall is composed of peptidoglycan (PG), consisting of alternating N-acetylglucosamine and N acetylmuramic acid residue, cross-linked by peptide side chains. Biogenesis of bacterial cell wall is an intricate process performed by coordinated action of cell wall synthetic enzymes, lipid carriers and regulatory proteins. The synthesis of PG monomer beings in the cytoplasm by Mur family enzymes. Once synthesized, PG monomers are transported across the cytoplasmic membrane by specific lipid carriers into the periplasmic space, where they are incorporated into the existing cell wall by the action of penicillin-binding proteins. Many antibiotics target various steps in PG biogenesis. β-lactam antibiotics inhibit transpeptidases, and compromise structural integrity of the cell To generate PG monomers, bacterial cell requires both energy and biosynthetic precursors, both of which are provided by central carbon metabolism. However, cross talk between central metabolism and cell wall biogenesis remained unexplored until recently. Maintaining a constant supply of central metabolites is crucial for optimal growth. Recent studies have shown that central metabolites can also be involved in a wide range of enzymatic reactions inside cells. In addition to serving as substrates in their primary pathways, these metabolites can be by-products of reactions in other pathways. It is proposed that moonlighting enzymes may indirectly promote or inhibit septal PG synthesis in a metabolite-dependent manner Studies have shown that levels alpha-Ketoglutarate (KG) cells is closely linked to cell morphogenesis. In C. crescentus, an excess of KG has inhibitory effect on m-DAP synthesis, ultimately affecting PG synthesis. There are evidences now that central metabolism is also linked to antibiotic resistance too. In recent years, Caulobacter crescentus has emerged as a powerful model to address the questions pertinent to spatio-temporal regulation of enzymes. C. crescentus although is non-pathogenic bacterium, it displays high resistance to beta-lactams Our research has have shown that Calulobacter cells deficient in lytic transglycosylase exhibit diminished resistance to ampicillin, suggesting a crucial role of PG recycling in cell wall homeostasis. Our study uncovered a that the defects in PG recycling could distress the de novo PG synthesis pathway and decrease levels of both UDP-MurNAc and UDP-GlcNAc levels upon antibiotic treatment. Growth in media supplementation with GlcNAc was able to rescue antibiotic sensitivity PG recycling mutants, suggesting that C. crescentus may recycle sugar moieties to generate PG monomers. Collectively, these results suggest a direct link between PG recycling and PG synthesis and central metabolism pathways in C. crescentus. Our working hypothesis that C. crescentus central carbon metabolites influence cell wall homeostasis and antibiotic sensitivity. Specifically we will study the following objectives: Objective 1: To investigate the role of N-acetylglucosamine metabolite in beta-lactam resistance in Caulobacter crescentus Objective 2: Role of tricarboxylic acid cycle intermediates in antibiotic resistance in C. crescentus Objective 3: Regulation of peptidoglycan precursor synthesis and cell wall homeostasis. This proposal aims to understand the role of central carbon metabolism in maintaining cell wall homeostasis. Using genetics, metabolomics, and high-throughput Transposon mutagenesis, we try to delineate how the TCA cycle and its metabolites influence cell wall synthesis and antibiotic resistance. The study, while fundamental in nature, has immense potential to unravel new genes and pathways involved in AMR.