The Requirements for Growth
- Microbial growth refers to the number of cells, not the size of cells
- Nutrients, moister/temperature limits bacteria growth
- Essential Elements (compounds a microbe cannot make itself by must gather from its immediate environment): Carbon, Nitrogen, Phosphorous, Hydrogen, Oxygen, and sulfur. They are needed in large quantities (macronutrients) because they make up the carbohydrates, lipids, nucleic acids, and proteins of the cell. All cell use these building blocks but build themselves in different ways.
Obtaining carbon: Autotrophy and Heterotrophy
* Metabolic groups; each group converts carbon to a form that the other groups can use
--> Rely on other organism to make organic compounds, such as glucose, that they use as carbon sources.
--> All bacterial pathogen are heterotrophs
--> During heterotrophic metabolism, organic carbon sources are disassembled to generate energy and then reassembled to make cells constituents such as proteins and carbohydrates.
--> This process converts a large amount of the organic carbon source to carbon dioxide, which is them released into the atmosphere.
--> If left alone, heterotrophs would deplete the world or organic carbon sources (converting them to unusable CO2) and starve to death. For life to continue, CO2 myst be recycled.
--> Use the CO2 by heterotrophs to make complex organic compounds (C, H, and O)
--> The organic compounds synthesized by autotrophs can later be used as carbon sources by heterotrophs
Physical Requirements for growth:
- temperature, pH, Osmolarity, Oxygen, pressure
- Certain organisms can survive 'extreme' temperatures
--> Change in temperature impact every aspect of microbial physiology, including membrane fluidity, nutrient transport, DNA stability, RNA stability, and enzymatic structure and function.
--> Every organism has an optimal temperature at which it grows most quickly, as well as minimum and maximum temperatures that define the limits of growth.
--> At cold temperatures, growth ceases because enzymatic processes become too sluggish and the cell membrane less fluid.
--> Heat increases molecular movement within proteins. Too much or too little movement will interfere with enzymatic reaction.
- By their range of growth temperature, microorganism can be classified as linking hot (thermophiles), cold (psychrophiles), or in between (mesophiles)
--> Thermophiles have adapted to growth at high temperatures typically 55 C and higher
--> Psychrophiles hare microbes that grow at temperatures as low as 0 C, but their optimal growth temp. is usually around 15 C
--> Mesophiles optimal range between 20 C - 40 C with a min of 15 C and max of 45 C (E. coli) -- easy to grown and human pathogens are mesophiles
1. Obligate anaerobe: Cannot grow with presence of O2
2. Facultative anaerobes: Can live with or with out O2 because they come equipped with enzyme that destroy toxic oxygen byproducts
3. Aerotolerant anaerobes: sub class of facultative organisms; use only fermentation (not aerobic fermentation) to provide energy
4. Strict anaerobe: dies int he least bit of oxygen
5. Microaerophilic: will only grow at low O2 concentrations; needs O2 by can only grow at atmosphere level
- Some microbes are halophiles (requires high salt concentration)
--> Most bacteria prefer NaCl concentration between 0.05-1M but halophilic microbes grow optimally at 0.85-3.4 M
--> E. coli can grow in high concentrations
- Most human pathogens thrive at 7.4 (blood)
- Some bacteria are acidophiles (bacteria and arches that live in acidic environments
- Too much acid or base is harmful to cells. Despite that sensitivity to pH extremes, living cell can tolerate a greater range of H+ concentration than of virtually and other chemical substances.
** Heliobacter pylon causes stomach ulcers, thrive at pH 1
**Lactobacillus maintains vaginal pH at 3-5, not a lot of bacteria in this environment, this bacteria eliminates a lot of bacteria growth.
- Barophiles: Microorganism at location deep within ocean floor that have adapted to grow at oppressively high pressure
--> actually require elevated pressure to grow, whereas barotolerant organisms grow over the range of 10-500 atm., but grows fall off there after.
- Microbes often live in communities as biofilms
- A biofilm is a mass of bacteria that stick to and multiply on a solid surface
- Biofilms can be constricted by a single spices or by multiple collaboration species and can form on a range of organic or inorganic surfaces
- Biofilm is build up that bacteria secrets; waste products form bacteria benefits other bacteria
- The matrix of the biofilm is composed of polysaccharides, proteins, and nutrients
- As more and more cells bind to the surface, they can begin to communicate with each other by sending and receiving chemical signals in a process called QUORUM SENSING
- Individual cells continually make these chemical signal molecules, but once the population reached a certain number the chemical signals reaches a concentration that the cells can sense
- Only certain types of bacteria produces biofilms
- Creating different kinds of gradients within a biofilm slows down O2 and nutrients (not only antibiotic resistant)
- Importance? When bacteria get together like this, they start swaping genetic information
- This is bad because they create new strains that is drug resistant and there may not be cure for it.
- Endospores are specialized "resting" forms of cells formed during sporulation form vegetative cells
- Endospores are highly durable, dehydrated from the cells with a "spore coat"that can survive extreme heat, lack of water, and exposure to chemical and radiation
- Endospores can survive for millions of years to germinate
- Only formed by gram-positive bacteria under extreme circumstances
- Bacillus anthracis, Clostridium tetani, C. botulinum
- occurs because cells do not immediately reproduce a new medium
--> No growth (bacteria is adjusting)
--> Cells taken from an aged culture may be damaged and required time for repair before they can replicate
- Cells do not dormant in lag phase
- cells preparing for new growth medium
Log phase (exponential growth):
- Once cells have retooled their physiological to accommodate their new environment, they begin to grow exponentially and enter log phase
- Exponential growths is balanced growth, where all cell component are synthesized at constant rates in relation to each other
- cells grow at the maximum rate possible based on the medium and growth condition provided (such as temp, pH, and osmolarity)
- Cells are larges at this stage of growth
- Generation time reaches a constant
- The bacteria growth curve is a line
- The stationary phase exhibits a balance between cell death and cell growth
- The exhaustion of nutrients, accumulation of waste products, and harmful pH change is usually responsible
- At this point, the growth curve levels off
- As they enter this phase, many bacterial pathogens develop resistance to antibiotics and host defense
- The death phase exhibits more cell death that cell growth
- Like growth rate, the death rate, the rate at which cell dies is exponential
- Exact death rates are difficult to define because mutations arise that promote survival, and some cells grow cannibalizing others.
**Low G/C gram positive
- Most are heterotrophs with thick cell walls that resist dying
- Many, such as Clostridium, form dormant endospores
- Grow as well-defined rods or cocci
- Some species of Firmicuties form endospores, inert heat-resistant spree that can remain viable for thousands of years. The endospores also resist dying, high-energy radiation, freezing, and chemical disinfectants
**High G/C gram positive, including major
- The acid-fast property is associated with using cell wall lipids
- Figure 10.9 - Dark blue droplets on the colonies contain secreted antibodies on strepetomyes
--> Streptomyces bacteria grow as filaments the develop specialized cells at their tips called arthrosproes, which are released and disperse in the air to form new colonies
--> The mycelia of streptomycin and other actinomycetes produce molecules we use as antibiotics
- Used as a defense mechanism against other bacteria
- These antibiotic producing bacteria prevent other antibiotics to kill them.
- They become antibiotic resistant by picking genes up from other bacteria that have antibiotic genes
- Other filamentous actinocyctes are pathogens. For example, Nocardia species are opportunist that can cause pneumonia in hospital patients.
Examples of Actinobacteria
-Do not gram stain well
- action bacteria include the causative agent of tuberculosis (M. tuberculosis) and leprosy (M. leprae)
--> cells of M. tuberculosis can be deleted by the acid-fast stain as tiny rods
--> M. tuberculosis has exceptionally thick, complex membrane that include some of the longest-chain acids
- Mycolic acid (a polymer of sugar build onto the peptidoglycan)
--> forms a waxy coat that impacts the entry of nutrients through porins and thus slows the growth rate, but also protects the bacterium from host defenses and antibiotics
--> For this reason, the curve for tuberculosis requires an exceptionally long course of antibiotics therapy
1st EditionDay, Stewart
6th EditionDavid L Nelson, Michael M. Cox
10th EditionCain, Campbell, Minorsky, Reece, Urry, Wasserman
1st EditionDay, Stewart