Chapter 8: Molecular Aspects of Microbial Growth

Bacterial cell division occurs primarily through binary fission and requires tightly regulated chromosome replication initiated at the origin of replication, followed by accurate chromosome segregation to ensure each daughter cell receives a complete genome. Central to the division process is the divisome, a protein complex organized around the cytoskeletal protein FtsZ, which forms a contractile ring that defines the division site and guides septum formation. Additional proteins such as FtsA, ZipA, and penicillin binding proteins participate in cell wall synthesis and septum construction during cytokinesis. The chapter also explores the molecular determinants of bacterial morphology, highlighting cytoskeletal proteins such as MreB and crescentin that guide peptidoglycan synthesis and contribute to the diverse shapes observed among bacterial species. Peptidoglycan biosynthesis is described in detail, including the transport of cell wall precursors across the cytoplasmic membrane, enzymatic insertion into existing cell wall structures, and cross linking reactions catalyzed by transpeptidases. Beyond basic growth processes, microorganisms exhibit complex developmental programs such as endospore formation in Bacillus, where nutrient limitation triggers a regulatory cascade controlled by Spo0A and multiple sigma factors that coordinate gene expression between the mother cell and forespore. Additional examples of microbial differentiation include the Caulobacter life cycle with swarmer and stalked cells and heterocyst formation in cyanobacteria specialized for nitrogen fixation. The chapter further investigates microbial biofilm development, a multicellular lifestyle in which cells attach to surfaces and produce extracellular polymeric substances to form structured communities regulated by signaling molecules and regulatory nucleotides such as cyclic di guanosine monophosphate. Finally, the chapter addresses antibiotics and their molecular targets, including DNA replication, transcription, translation, cell membrane integrity, and cell wall synthesis, along with mechanisms of antibiotic resistance such as target modification, enzymatic drug inactivation, efflux pumps, and metabolic bypass pathways. The discussion concludes with persistence and dormancy, explaining how toxin antitoxin systems and stress responses allow small subpopulations of cells to survive antibiotic exposure through temporary metabolic inactivity.