Microbial Growth: Cell Division and Population Growth

Industry Uses

- Human growth hormone production - Antibiotic production - Beer and wine making - Soy sauce making

Bacterial Growth Plots

1. Bacterial growth plots are usually represented in a linear model 2. On the plot, the straight line represents that the cells are in an exponential phase of growth - As time increases, the # of cells also increases 3. Direct extrapolation of the generation time can be done from a semi-log graph of exponential growth Semi-log graph = One axis is linear, the other is logarithmic Graphical extrapolation = The process of identifying a time range during which the cell population has doubled

Microbial Growth Cycle: Stationary Phase

1. Balance between cell division and cell death 2. Cause = Physiological adaptations to survival - The cell use the nutrients provided and create toxic wastes that eventually accumulate

Binary Fission: Budding

1. Budding division results from unequal cell growth and forms totally new daughter cell, compared to the original cell 2. There are 5 main types of division and 4 main types of budding, grouped according to equal or unequal products of the cell division Equal Products (A) Binary Fission - MOST bacteria use this method Unequal Products (B) Simple budding = budding forms at the polar end of a cell (C) Budding from hyphae = long filament-like structure is produced on the original cell, and then a bud breaks off from the filament (D) Stalked division = the original cell has a stalk extension, but the bud breaks off from the cell part not the stalk, and the new daughter cell contains a flagella for motility (E) Polar growth WITHOUT differentiation of cell size = bud forms from one pole of the cell, but the bud is always the same size as the original cell (it doesn't start out small and get bigger, like in sumple budding)

Microbial Growth Cycle: Exponential Phase

1. Cell and mass double in each generation 2. Very uniform population 3. Faster growth rate happens in a complex medium than in minimal medium 4. Exponential growth rates vary 5. Microbial growth is under precise control

Microbial Growth Cycle: Death Phase

1. Cells start dying 2. Death phase is exponential = linear 3. Viable count (number of LIVING cells) declines FASTER than turbidity, because the dead cells add to the turbidity 4. Surviving cells can resume growth in fresh medium

Exponential Growth

1. Exponential growth = growth of a microbial population in which cell numbers double within a specific time interval 2. A relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth: N = N0 x 2n - N is the final cell number - N0 is the initial cell number - n is the number of generations during the period of exponential growth

Bacterial Growth by Binary Fission

1. Growth means to increase in the number of cells 2. Bacteria can perform up to about 2,000 simultaneous biochemical reactions at 1 time 3. Binary Fission = bacterial cell division mechanism - All cell constituents increase PROPORTIONALLY = everything present in the original cell is present in the new cell - The generation time for an organism varies

Batch Cultures in Industrial Microbiology

1. Large-scale batch cultures are grown in FERMENTORS 2. Fermentors... - Can be 1-500,000 liters or more - Require mixing and O2 monitoring - Temperature is controlled - Sterilization-in-place - Contain sampling and harvest ports - Require pH monitoring and control - Steam can be added to prevent dryness - Contain cooling water inports/exports 3. Fermentors can be used to produce human growth hormones, which use to be extracted from cadavers before fermentors were invented

Microbial Growth Cycle: Lag Phase

1. Metabolic adjustment 2. Length of lag phase can change - Moving from a minimal medium to a complex medium results in a longer lag phase - Moving from a complex medium to a minimal medium results in a shorter lag phase

Microbial Growth Cycle

1. Microbial cell growth is usually done in BATCH culture Batch culture = a closed-system microbial culture of a fixed (known) volume -Growth in a batch culture is under PRECISE control - In a batch culture, nutrients and consumed by the culture and waste accumulates 2. The typical growth curve for a population of cells grown in a batch culture has 4 different phases: (A) Lag Phase (B) Exponential Phase (C) Stationary Phase (D) Death Phase

Peptidoglycan Synthesis and Antibiotics

1. Peptidoglycan is a macromolecule unique to bacteria. Its synthesis is a target of antibiotics 2. Bacitracin = is an antibiotic that inhibits the function of bactoprenol - This means that the G-M precursors cannot be connected to the existing peptidoglycan - The peptidoglycan layer will stop being synthesized 3. Penicillin = inhibits the transpeptidase enzyme, halting the formation of crosslinks in the peptidoglycan - Transpeptidase is also known as penicillin-binding protein - In the presence of penicillin, some growing cells increase production of autolysins, resulting in cell lysis

Peptidoglycan Precursors

1. Peptidoglycan precursors are synthesized in the CYTOPLASM and transported through the cytoplasmic MEMBRANE 2. G-M-pentapeptide precursor units are attached to Bactoprenol - Bactoprenol = lipid molecule that can pass through the membrane to reach the outer layer 3. Bactoprenol transports the precursor unit across the cytoplasmic membrane 4. Autolysins = make holes in peptidoglycan so that the new unit can be attached - They hydrolyze the 1,4-β linkage between the G and M sugars (NAG and NAM) 5. Transglycosylase = connects the AMINO SUGARS of the precursor to the EXISTING peptidoglycan strands 6. Transpeptidase = connects the PEPTIDE PORTION of the PRECURSOR to form CROSSLINKS in peptidoglycan

Planktonic vs. Sessile Growth

1. Planktonic growth = Growth as suspension, suspension in some sort of liquid 2. Sessile growth = attached to a surface - Can develop into biofilms (film growing on a surface) made of a polysaccharide (multi-sugar) matrix with bacteria embedded in it - Microbial Mats = are multilayered sheets with different organisms in each layer (ex. hot springs)

Generation Time

1. The generation time is the time it takes for 1 cell to divide into 2 - Varies depending on the microorganism AND its environment - Generation time = DOUBLING time - Generation times are much longer in nature compared to labs 2. Generation time (g) of an exponentially growing population is: g = t / n - t is the duration of exponential growth (days/hours/minutes) - n is the number of generations during the period of exponential growth

Biofilms

Biofilms form in stages 1. Planktonic bacteria attach to a surface 2. Cell-to-cell adhesion takes place and begins to form a sticky matrix of polysaccharides and proteins 3. Proliferation = multiplication and spreading 4. Maturation = complex groups form, bacterial cells begin growing flagella for disperion 5. Dispersion of the new bacteria takes place Biofilms help PREVENT harmful chemicals from penetrating the bacteria, prevent protists from eating the bacteria, and prevent washing away of cells Biofilms affect human health, water distribution systems, and fuel storages

Genome Replication in Fast-Growing Cells

In SLOWLY growing cells... - DNA replication happens with a SINGLE replication fork - Chromosome replication is at the same pace with the cell's overall division - g = 1 hr But In RAPIDLY dividing cells... - MULTIPLE replication forks occur, causing the chromosome replication rate to SPEED UP - Cells can contain more than 2 complete chromosomes at one time - g = 20 min E. Coli chromosomes replicate in about 40 minutes, but in some cases the cells divide faster by using the RAPID division method, making the generation time 20 minutes