Microbiology Bacterial Growth
Mesophiles
-"middle lovers" -Abundance of pathogens begins.
Hyperthermophiles
-"superheat lovers" -95C optimum temperature -range from 68 C to 105 C
Caulobacter
This bacteria takes out the plasma membrane. This increases the surface to volume ratio. This is a benefit because the nutrients have to cross the plasma membrane. The more membrane, the more efficient transport through transport proteins. Not all bacteria have this benefit.
Purpose of Petroff Hausser experiment
A technique to obtain total cell count by calculating cell/unit volume. This does not establish living or dead cells, just the amount of cells.
BHI broth
Adds lots of nutrients to the bacteria for them to continue into the log and stationary phase.
Three types of ways to measure growth experimentally
1. Obtain Total Cell Count--Petroff Hausser, Not able to check whether the cells are living or dead unless working on a growing sample because they have to be alive to replicate. 2. Get Viable Count--Get DF and plate dilutions to count colonies. Only Live cells 3. Cell Mass--this is done using a spectrophotometer. The tubes with the bacterial culture are bombarded with light at a certain wavelength. The more cells, the more absorbance. This includes live and dead cells.
Environmental Factors that Affect Bacterial Growth
Nutrient Availability, Temperature, pH, Oxygen Availability, Water Activity
aerotolerant anaerobe
Oxygen and Growth -There is a evenly spread out concentration. -They can grow with or without oxygen. The presence of oxygen does not alter their growth
Obligate Aerobe
Oxygen and Growth -Absolutely ALWAYS requires oxygen for growth. There is a built up concentration of bacteria towards the top of the tube
Microbe Aerophiles
Oxygen and Growth -Need oxygen, but the amount they need is less that what is available in our environment. -There is a concentration gradient throughout one area of the tube. They find where they can grow best in the tube and grow in that area.
Strict anaerobe
Oxygen and Growth -These bacteria only grow in the absence of oxygen. They are killed by the presence of oxygen -There is a larger accumulation of bacteria at the bottom
Facultative anaerobe
Oxygen and Growth -may be able to grow without oxygen, but if they are given a source of oxygen, they prefer to use that oxygen. -There is growth throughout the agar, but there is a greater concentration at the top.
Some Bacteria are killed by oxygen
Oxygen metabolism leads to toxic products -Oxygen is poisonous to cells. When we oxidize it, it creates toxic intermediates which damage cell parts. 1. Superoxide (most toxic)--When oxygen reacts with electrons 2. hydrogen peroxide--reacting with protons and electrons 3. Hydroxyl radical--reacting with hydrogen peroxide and electrons and protons
Effect of water activity in bacterial growth
The amount of water available to the cell. Factors that can affect Aw are osmolarity and evaporation (Increase in evaporation, lowers water activity) -Pure water has Aw of 1 and dry water has Aw of 0
Oligotrophic
bacteria that survive with limited nutrients (Limited nutrients in log phase). There is lots of competition for nutrients because they live in communities. Bacteria will not be in balanced growth.
water activity of selected prokaryotes
many microbes grow in Aw of less than 0.9 (halo tolerant)--these are found in the human body. E Coli in has a Aw of 0.93; If put in 0.8, it will not grow. -Halophiles cannot grow in a higher water activity, only lower.
Measurement of population growth
measured by measuring cell number or cell mass. Get geometric increase in cell number
Neutralophiles
pH is acidic outside the membrane relative to inside, there is more positive charge outside. When electrons flow down the electron transport chain, protons get pumped. (normal condition)
Thermophiles
-"hot lovers" -Optimal temperature: 60-65 - Can degrade organic matter -More saturated fatty acids in membrane -Archaea have tetra ether monolayers (more rigid than phospholipid bilayer) -Heat stable enzymes (Enzymes used in PCR is Taq polymerase. Optimal temp is 72C
Psychrophiles
-"philes"--love the cold. They have an optimum temperature of about 10C. -More unsaturated fatty acids in the membrane (resist forming gels at lower temperatures because they have the kinks when trying to gel) -enzymes adapted for low temperatures
Exponential phase growth
-As long as values are doubling, it does not matter. We look at the doubling time. -You can calculate all values by looking at the graph.
pH on bacterial growth
-Bacteria grow in neutral pH (neutralophiles--pH of 5.5-8) Buffers are used to neutralize pH -Fungi are more acid tolerant, so they can grow at a lower pH than bacteria -Bacteria maintain a neutral internal pH no matter what the pH of the environment is
Nutrients in the Lab
-Can be easily manipulated -there are two main types of medium: Chemically Defined--known amounts of each nutrient Complex Medium--unknown amounts of each nutrient -The more premade components available in the medium, the shorter the doubling time.
Halotolerant
-Can survive in 7.5% salt -Needs to increase internal solute concentration -produces compatible solutes inside the cell. -Not permanent; the solute concentration can go up and down
Asynchronous Growth
-Exponential growth -Bacteria dividing at the same rate, but not at the same time
How do microbes grow?
-It does not want to lose any water, so it increases internal solute concentration to help withstand the lower Aw -it concentrates the solute that is not toxic to the cell
How aerobic bacteria protect themselves from toxic oxygen
-Possess enzymes that can remove toxic oxygen products. -Cells detoxify if different ways: 1. Get rid of hydrogen peroxide--using the catalase (enzyme) to get rid of hydrogen radical 2. Get rid of superoxide dismutase--this produces hydrogen peroxide--obligate anaerobes don't have this 3. Strict anaerobes don't have a way to get rid of these intermediates, so they are killed
Temperature and bacterial growth
-Prokaryotes grow in the range of -7C to 120C. Each bacteria grow in a more narrow range - increase in temperatures, the proteins can denature and then becomes non-functional -After you reach the optimum temperature, the bacteria starts to grow. A decrease in temperature, decrease in metabolic processes, the membranes are less fluid.
How bacteria maintain a neutral internal pH
-Proton Motive Force 1. pH gradient--protons affect charge gradient
Synchronous Growth
-Step growth -Everything happens at the same time. This is called the step growth because the cell divides which doubles in number every time they grow -This is hard to do. We have to dilute to one cell.
Psychrotrophs
-This is the temperature in the fridges and they have an optimum temperature of 20-25.
Halophile
-can survive in 6 M salt concentrations. -They have to be able to hold onto the water. Cells proteins have evolved to not denature at high salt concentrations, which means they can survive those conditions.
Exponential Microbial Growth
-helps determine viable count g=viable count/time -you can find doubling time with a linear line -
Alkalophiles
-optimum 8.5-14 -High carbonate soils and soda lakes. -fewer H+ ions inside than outside. Protons want to leave, you want to keep them here. They swap charge for charge. They bring in a proton and let out Na+ to help maintain the proton concentration.
Acidophiles
-optimum pH: 0-5.5 -Acidic environments like hot springs -more concentration outside than inside—they want to flow in, through transport proteins. They bring another ion and it flips the charge gradient—there is more positive charge outside than inside. So all the H+ doesn't come rushing inside.
Binary Fission
Bacterial cells divide through binary fission and as cells grow in size, the DNA is replicated.
Osmolarity
How much solute is present so that it can affect water activity. This determines which way the water is going to flow. -adjusting solutes in a solution can affect water solubility
Microbial Growth Curve
This growth cycle occurs in a closed system. 1. Lag phase--No net growth; cells don't divide at a constant rate; cells have to adjust to new environment; not all cells divide at the same rate (adjustment phase)--Asynchronous growth. 2. Exponential (Log) Phase--Sychronous growth; culture grows exponentially; Time between each cell is the same; There are lots of nutrients; This is where doubling time is calculated; bacterial cells are living in their own waste. 3. Stationary Phase--They run out of nutrients; There is no more growth; they are unhappy because they are living in waste; sporulation occurs; this phase can last a long time 4. Death Phase-- They finally start to die off once waiting long enough.
