Microbial Growth Flashcards
population growth
Populations of unicellular microorganisms increase exponentially by geometric progression (2n)
exponential growth
asynchronous culture
synchronous culture (will finally become asychronous)
Growth rate or doubling time or Generation time
period required for a cell to enlarge, divide, and produce two daughter cells
-variable between different bacteria
-all cell in one population have the same doubling time
-varies with the nutrient availability:
-Less nutrients, doubling time increases
-Accumulation of toxic metabolic compounds, doubling time increases
-E. coliin the lab (18 mins) vsin the gut (12 hours)
-When nutrients are all consumed growth stops
Growth curve or phases of growth
lag phase
exponential or log phase
stationary phase (plateau)
Death phase
Lag phase
time for cells (stationary or death phase) to adjust to fresh or new medium, start or adjust their metabolism (protein synthesis, DNA replication), and start dividing
A longger lag phase will cause by:
*Inoculum taken from an old culture
*Inoculum taken from a rich medium and added to a poorer one
* No Lag occurs when growing cells are transferred from a poor to a richer medium
*Inoculum taken from a chemically different medium
*Inoculum taken from refrigerated cells
*Cells inoculated into a cold medium
log phase
period where nutrients are not in limiting amounts and where cells divide at their maximum speed (lowest doubling time)
Stationary phase (plateau)
The culture gradually switch from the log to the stationary phase when nutrient concentration is limiting and toxic waste accumulates, cells divide slower and eventually stop (doubling time increases gradually)
Death phase
nutrients where completely consumed, cells stopped growing (stationary phase), and now cells are starting to burst and die (exponentially), not all cells die
Continuous culture in a chemostat
*Concentration of one of the nutrient should be provided in limiting amounts to reduce growth rate
*All nutrients (culture medium) should be provided continuously at the same rate to the growing culture
*Some of the growing culture (cells and waste products) should be removed continuously at the same rate
Growth rate is constant and equals loss rate, same amounts of cells actively growing
Uses of continuous culture
*Provide a constant supply of cells in balanced growth (exponential phase) and growing at a known growth rate
*Study bacterial growth at variable and very low nutrient concentrations, resemble the environment bacteria encounter in nature
*Facilitate research in microorganism interactions and ecological situations
*Allow industrial production of food and metabolites continuously (antibiotics, vitamins, ethanol）
Parameters affecting bacterial growth
- temperature
- hydrogen ion concentration (pH)
- gas environment
temperature
Hyperthermophiles (95°C)
Thermophiles (65°C)
Mesophiles (37°C)
Psychrotrophs(25°C)
Psychrophiles (10°C)
pH
Neutrophiles (pH around 7.0)
Acidophiles (pH below 7.0)
Alkalophiles(pH above 7.0
Gas environment
Aerobes (need oxygen)
Anaerobes (need anaerobic conditions)
Facultative anaerobes (with or without oxygen)
Capnophiles (need oxygen and high CO2concentrations)
温度和growth rate趋势
最佳温度越高，最高的growth rate越高
Reactive Oxygen Species （ROS）
superoxide radical
hydrogen peroxide
hydroxyl radical
These can hydrolyze all of the molecules we can find in cells
什么pH区间可以抑制生长
> =11
Protective enzymes
Superoxide dismutase (SOD）
2O2- + 2H+——>O2 + H2O2
Catalase
Peroxidase
2H2O2——>2H2O + O2
H2O2 + NADH + H+——>H2O +NAD+
Oxygen and bacterial growth
+SOD +catalase
+SOD +Catalase
+SOD -Catalase
-SOD -Catalase
+SOD +/- Catalase(low levels)
Obligate
Facultative anaerobe
Aerotolerant anaerobe
Strict anaerobe
Microaerophile
bacteria grow in liquid culture, put in agar
The anaerobic jar
Rubber gasket seal
lid
Catalyst chamber (containing palladium pellet， 催化H2和O2生成水)
Gas generator envelop
anaerobic indicator strip（methylene blue）
Growth on solid vs liquid media
In liquid cultures, all cells are in the same condition
On a petri dish cells in a colony face different conditions
-Cells in the center are in the stationary phase or death phase
-Cells on the edge are actively growing (exponential phase)
-Cells at the surface are in aerobic conditions
-Cells under the surface of the colony are in anaerobic conditions
Mass measurement
Turbidity
colony number
Mathematics of cell growth
Starting with a single cell, the total population number (Nt) at the end of a given time period would be
start with single cell
Nt= 1 x 2^n
start with more than one cell
Nt= N0x 2n
n = 3.3 (log Nt-log N0)
log2=0.301
Gene vs. Genome vs. Genotype vs. Phenotype
DNA segment that codes for a protein, ribosomal RNAs (rRNAs), or transfer RNAs (tRNAs)
complete DNA sequence present in a cell or a virus
the specific set of genes of an organism
observable characteristics
