ch7 - Microbial Growth What is Microbial Growth? Defined as...

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Unformatted text preview: Microbial Growth What is Microbial Growth? Defined as an increase in number Achieved by: Binary fission most Bacteria Budding Cell duplicates its components, then shares them between 2 daughter cells Daughter cells become independent when septum forms between cell halves Binary Fission vs. Budding Binary fission Two equal daughter cells Budding Two unequal cells mother and daughter Buds at end of prosthecae Baeocytes with basal & apical cells Bacterial Cell Cycle Chromosome replication C phase: replication D phase: delay period; nucleoid partitioning Cytokinesis Septation complete Chromosome Replication Begins at the origin of replication Usually single origin per chromosome Chromosome moves central to cell DNA synthesis proteins associate with chromosome = replisome Bi-directional replication proceeds to make 2 copies of the original chromosome Chromosome Partitioning MreB model in rod-shaped bacteria MreB is analogous to eukaryotic actin MreB forms spiral complex within the cell Origin of each replicated chromosome binds to MreB Chromosomes separated to bacterial poles as they move along the MreB helix Evidence: MreB mutants cannot segregate chromosomes from one another Steps in Cytokinesis in E. coli 1. Select site where septum will form MinCDE limits formation to cell center [dense] at poles, but none at center 1. Assemble of Z ring Ring composed of FtsZ 1. Link Z ring to plasma membrane 1. Assemble cell wall synthesis machinery 1. Constrict cell and form septum Batch Culture Growth Curve Growth Phases: Lag Log (Exponential) Stationary Death (Decline) Easily measured during growth in liquid media by spectroscopy or densitometry Log vs. Arithmetic Scales Conversion to log scale compresses the distance between data points evenly. Lag Phase Metabolically active cells but NO increase in number Adaptation: induce enzymes needed; synthesize new ribosomes, ATP, and cofactors; replicate chromosome Repair cellular components, increase in cell size Length of entire phase varies w/ species & environmental conditions Log (Exponential) Phase Population doubles each generation Generation (doubling) time ranges from 7 min to 20 hr Average is 20 min Growth is asynchronous- not all cells divide at exact same time Growth rates are saturated Limited to [celluar enzyme] Balanced growth- all cellular constituents made at constant rates to one another May change to unbalanced growth if one nutrient becomes limiting Stationary Phase Curve becomes horizontal Population growth ceases New cells made at same rate as old cells die growth rate = death rate Reasons for stationary phase: Nutrient limitation or O 2 limitation Accumulation of toxic wastes Cell density Stationary Phase (cont.) Very common in nature (oligotrophic environments)...
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ch7 - Microbial Growth What is Microbial Growth? Defined as...

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