Environmental influences on microbial growth

Question 1

differences in growth rate are determined by:

Answer 1

• nutrition and niche-specific physical parameters like temp and pH

*micrboes have has >3.5B years of evolution and have evolved adaption mechanisms for life in virtually all earths ecosystems (unlike eukaryotes)

*some hot spring bacteria can double in 10 min while some in deep sea sediment may take 100 years

Question 2

What are the normal growth environmental conditions

Answer 2

• sea level (atmospheric pressue, oxygen saturation)
  temp: 20-40 C
• near neutral pH
• 0.9% salt and ample nutrients

* ecological niche outside this window = extreame, and organims living in that are extremophiles (usually bacteria and achea)

Question 3

the environmental habitat that a species inhabits is based on _____

Answer 3

based on tolerance of that organisms portiens and other macromolecular structures (like cell membrane lipid diversity, stability of nucelic acids) to the physical conditions within that niche

^adaptive mechanism allow organisms ocmponents to function properly

• multiple extremes in the environment can be met simultaneously (extreame temp, low pH, anaerobic)

Question 4

what is bioinformatics, what does it allow us to study

Answer 4

• uses the DNA sequence of a gene to predict the function of its protein product
• allows us to study the biology of organisms that we cannot culture
• obtain the DNA seq- predict the genes and resulting protein, compare that protein to bacteria in data base which have been well studeid (can give an idea of the function of that protein and what the bacteria does)

Question 5

what are global approaches to study gene expression

Answer 5

• allows to view how organisms respond to changes in the environment
• Knowing which genes/proteins are expressed in a given situation reveals how microbes grow under different conditions and defend themselves against environmental stresses.
• comparing gene expression of unknown organisms to that of known organisms - how is expression of particular protein effected when there is pH change, osmolarity change etc.
• gives idea of how bacteria responds to stresses

Question 6

how are microbes commonly classified

Answer 6

• by environmental niche
• set of conditions like: habitat, resources, temp, relations with other species etc

Question 7

what are the classifications of microorganisms in the growth temperature ranges

Answer 7

• Psychrophiles: growth range ~0°C–20°C
• Mesophiles: growth range ~15°C–45°C
• Thermophiles: growth range ~40°C–80°C
• Hyperthermophiles: growth range ~65°C–121°C

*all organisms have membranes and proteins best suited for their temperatures

*note want to pay attention to psychrophiles bc if in food will still grow in the frige

Question 8

what is important about abcterial cells and their body temperatures

Answer 8

• bacterial cells cannot control their body temperature
• call temperature matches that of its immediate environment
• prokaryotes ahve evolved adaptions for their optimal temperature environemnt

Question 9

how does temperature effect physiolgoy of microbed

Answer 9

• impacts every aspect of microbial physiology (membrane, DNA, rptoein stability, enzyme rate of catalysis
• cardinal temperatues define the gorwth limits/range of an organism
• there are minimu, max and optimum temps
• typical temp growth range usually spens the optimal growth temp by 30-40 degrees
• A species grows most quickly & optimally at temperatures where all of the cell’s proteins work most efficiently

*growth stops when temp causes critical proteins,genome or cell structures to fail

Question 10

relationship between temp and growth rate

Answer 10

• thermodynamic principles liit a cell’s growth to a narrow temp range
• optimum: replication and proteins can not work any faster

Question 11

Describe the Heat shock response

Answer 11

• caused by rapid temperature changes during growth that acitvate groups of stress response genes

*this response is documented in all organisms examined so far

• the protein products of these genes include chaperones that maintain protein shape and enzymes that change membrane lipid composition

Question 12

what is water activity

Answer 12

measure of how much water is availble for use

• typically measued as the ratio of the solutions vapour pressue relative to that of pure water (=1)

*if oslution has lots of solutes, most of water is tied up to water activity decreases

• most bacteria require water activity levels > 0.91
• fungi can tolerate water activity levels >0.86

Question 13

relationship between osmolarity and water activity

Answer 13

• inversley related
• osmolarity = number of solute molecules in a solution
• high aw environlems have low solute conc (hypotonic relative to cell cytoplasm)

Question 14

water moving in cell in hyper vs hypotonic environments

Answer 14

• membrane allows water to pass (by osmosis & via aquaporins) but NOT solutes (which require transporters
• in hypertonic, water will leave cell (plasmolysis occurs)
• hypotonic medium causes influx of water (inc cytoplasmic volume)

Question 15

what are the mechansims to reduce osmotic stress

Answer 15

1. hypertonic media

• bacteria protect their internal water by synthesizing or actively important comatible solutes from environment
• solutes allow normal physiological functions to occur, do allow that water to be moved

2. Hypotonic media
   * pressue-sensitive or machanosensitive channels can be used to leak solutes out of the cell

* outside of there osmotic comfort range, these houekeeping strategies become ineffective at controlling internal osmolarity

Question 16

What are Halphiles what do they require?

Answer 16

Halophiles have evolved and specialized for optimal growth in high salt conc environments

• 2-4M NaCl
• they must maintain a low internal cytoplasmic concentration of Na* (if take up too muhc salt will tie up to much water, proteins will be deprived of water and forced to precipitate out)
• have more compatable solutes in cytoplasm
• its the cell wall and cell membrnes that require the high salt environment to remain intact
• halophilic microbes use special ion pumps to excrete sodium and replace it wiht other cations like K+

Question 17

what are the classifications or organisms according to their pH

Answer 17

• Acidophiles: grow at pH 0-5 *often chemoautotrophs
• Neutralophiles grow at pH 5-8 *include most pathogens
• Alkaliphiles grow at pH 9-11 *typically found in soda lakes

* control the pH of their cytoplam

Question 18

what is the effect of pH on a cell’s physiology?

Answer 18

• exteme concentrations of either hyronium or hyroxide ions in solution will limit growth

= living cells tolerate a greater range in environmental concentration of H+ of virtually any other chemical substance

• all enzyme activities exhibit optima, minima and maxima with regard to pH
• bacteria reg internal pH to keep enzymes functioning normally - can tolerate a pretty decent pH range

( biologial membranes are relativey impermeable to protons, uncharged organix acids can readily cross membrane and dissociate in cell - releasing a proton and disrupting internal pH)

Question 19

how do microbes adapt to survival under extreame pH conditions?

Answer 19

• cell envelope components that ‘sequester’ the hydroxide and proton ions protect the fragile cytoplasmic membrane & protect cytoplasmic enzymes/macromolecules
• achea groups are the main prikaryotes ofund in extreame pH; membranes mage of diether lipids

*cell wall = acidic polymers and excess of hexosamines

*cell membrane = high levels of diether lipids

• microbes can prevent the unwanted influx of protons by using active transporters to exchange extracellular K+ for intracellular H+ when inteval pH too low (K+/H+ antiporter)
• under extreamly alkaline condiitons, the cells can use the Na+/H+ antiporter to bring protons into the cell in exchange for expelling Na+

Question 20

what are poly extremophiles

Answer 20

• foten an organism that is an extremophile for one environmental factor is an extremophile with reaspect to others as well
• Sulfolobus acidocaldarius is a thermophile (60°C to 95°C ) and an acidophile (pH 1-5); found in sulfur rich volcanic mud/hot springs

Question 21

role of oxygen in environment for microorganisms

Answer 21

• many microorganisms grow in absence of O2 anaerobes
• usually aerobes use O2 a terminal electron acceptor (TEA) in an Elecron transport system (aerobic respiration)
• some bacteria that generate energy via respiration use compounds other than oxygen as their TEA - process = anaerobic respiration

Question 22

benefits and risks of oxygen to microorganisms

Answer 22

• organisms can use it as a TEA to extract energy from nutrients
• Oxygen is toxic to anaerobes and to all calls without enzymes capable of efficiently destroying oxygen’s breakdown products (reactive oxygen species)
• ROS ex: singlet oxygen, superoxide, hydrogen peroxide, hydrozyl radicals
• ROS kills cells by seriously damaging DNA, RNA, rptoeins and lipids by stripping them of their electrons

Question 23

classifications of organisms in diff oxygen env

Answer 23

aerobic microbes= require oxygen

facultative microbes= can live wiht or without

microaerophilic microbes = use oxygen but low amounts

anaerobic microbes = do not tolerate, cant deal with ROS

Question 24

what are strict aerobes, microaerophiles, strict anaerobes, aerotolerant anaerobes and faculative anaerobes

Answer 24

• Strict aerobes can only grow in oxygen.
• Microaerophiles grow only at lower O2 levels.
• Strict anaerobes die in the least bit of oxygen.
• Aerotolerant anaerobes grow in oxygen while retaining a fermentation-based metabolism.
• Facultative anaerobes can live with or without oxygen.
• They possess both the ability for fermentative metabolism (no respiration required generate ATP via glycolysis) and respiration (anaerobic and aerobic).

Question 25

describe oxygen related growth zones in standing/media unstirred test tube

Answer 25

• take media and put in tube

cap tube and incubate a soil sample without mixing the contents

• observe where organisms are growing
• if you measure oygen in tube over time see oxygen zones