(drangela) bteriaac - 26 maret 2012
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bakteriTRANSCRIPT
Bacterial Anatomy, Nutrition, Growth, Metabolism and Genetics
Community Colege of Rhode Island
Bacterial anatomy
Generalized structure of a prokaryotic cell
Appendages: Cell Extensions The Flagella
3 parts filament
long, thin, helical structure composed of proteins Hook
curved sheath basal body
stack of rings firmly anchored in cell wall rotates 360o
1-2 or many distributed over entire cell functions in motility
Flagellar Arrangements1. monotrichous – single
flagellum at one end
2. lophotrichous – small bunches arising from one end of cell
3. amphitrichous – flagella at both ends of cell
4. peritrichous – flagella dispersed over surface of cell, slowest
Appendages for Attachment Fimbrae
fine hairlike bristles from the cell surface
function in adhesion to other cells and surfaces
Appendages for Mating Pili
rigid tubular structure made of pilin protein found only in Gram
negative cells Functions
joins bacterial cells for DNA transfer (conjugation)
adhesion
The Bacterial Surface Coating Glycocalyx Coating of molecules
external to the cell wall Made of sugars and/or
proteins functions
attachment inhibits killing by white
blood cells receptor
The Bacterial Surface Coating Glycocalyx 2 types:
1. capsule - highly organized, tightly attached
2. slime layer - loosely organized and attached
The Structure of the Cell Wall Peptidoglycan macromolecule composed
of a repeating framework of long glycan chains cross-linked by short peptide fragments
provides strong, flexible support to keep bacteria from bursting or collapsing because of changes in osmotic pressure
The Cell Envelope External covering outside the cytoplasm Composed of two basic layers:
cell wall and cell membrane Maintains cell integrity Two generally different groups of bacteria
demonstrated by Gram stain:Gram-positive bacteriaGram-negative bacteria
4 Groups Based on Cell Wall Composition
1. Gram positive cells
2. Gram negative cells
3. Bacteria without cell walls
4. Bacteria with chemically unique cell walls
Gram Positive Cell Wall
Consists of a thick, homogenous
sheath of peptidoglycan 20-80 nm thick
tightly bound acidic polysaccharides
including teichoic acid and lipoteichoic acid
cell membrane
Retain crystal violet and stain purple
Gram Negative Cell Wall
Consists of an outer membrane
containing lipopolysaccharide (LPS)
thin shell of peptidoglycan periplasmic space inner membrane
Lose crystal violet and stain red from safranin counterstain
Protective structure while providing some flexibility and sensitivity to lysis
Gram Negative Cell Wall
LPS endotoxin that may
become toxic when released during infections
may function as receptors and blocking immune response
contains porin proteins in upper layer
Regulates molecules entering and leaving cell
The Gram Stain
Differential stain Gram-negative
lose crystal violet and stain red from safranin counterstain
Gram-positive retain crystal violet and stain
purple Important basis of bacterial
classification and identification Practical aid in diagnosing
infection and guiding drug treatment
Atypical Cell Walls
Some bacterial groups lack typical cell wall structure Mycobacterium and Nocardia Gram-positive cell wall structure with lipid mycolic acid
pathogenicity high degree of resistance to certain chemicals and dyes basis for acid-fast stain
Some have no cell wall Mycoplasma cell wall is stabilized by sterols pleomorphic
Cytoplasm
dense gelatinous solution of sugars, amino acids, & salts
70-80% water serves as solvent for
materials used in all cell functions
Chromosome single, circular, double-
stranded DNA molecule contains all the genetic
information required by a cell
DNA is tightly coiled around a protein dense area called the
nucleoid
Plasmids
small circular, double-stranded DNA free or integrated into the chromosome duplicated and passed on to offspring not essential to bacterial growth & metabolism may encode antibiotic resistance, tolerance to
toxic metals, enzymes & toxins used in genetic engineering- readily manipulated
& transferred from cell to cell
Site of Protein Synthesis Ribosomes prokaryotic differ from
eukaryotic ribosomes in size & number of proteins
site of protein synthesis
all cells have ribosomes
Storage Bodies Inclusions & Granules intracellular storage
bodies vary in size, number &
content Examples:
Glycogen poly--hydroxybutyrate gas vesicles for floating sulfur polyphosphate granules
Endospores resting, dormant cells produced by some G+ genera
Clostridium, Bacillus & Sporosarcina have a 2-phase life cycle
vegetative cell endospore
sporulation formation of endospores
Germination return to vegetative growth
withstand extremes in heat, drying, freezing, radiation & chemicals
Endospores
resistance linked to high levels of calcium & certain acids
longevity verges on immortality 25 to 250 million years
pressurized steam at 120oC for 20-30 minutes will destroy
Microbial nutrition, growth, and metabolism
Microbial Nutrition nutrition
process by which chemical substances (nutrients) are acquired from the environment and used for cellular activities
essential nutrients must be provided to an organism
Two categories of essential nutrients:macronutrients micronutrients or trace elements
Microbial Nutrition
macronutrients required in large quantitiesrole in cell structure and metabolism proteins, carbohydrates
micronutrients or trace elementsrequired in small amounts involved in enzyme function and maintenance of
protein structuremanganese, zinc, nickel
Nutrients Inorganic nutrients
atom or molecule that contains a combination of atoms other than carbon and hydrogen
metals and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide) and water
Organic nutrients contain carbon and hydrogen atoms and are usually the
products of living things methane (CH4), carbohydrates, lipids, proteins, and nucleic
acids
Chemical Composition of Cytoplasm
70% water Proteins 96% of cell is composed of 6 elements:
CarbonNitrogenOxygenHydrogenPhosphorousSulfur
Obtaining Carbon
Heterotroph organism that obtains carbon in an organic form
made by other living organisms proteins, carbohydrates, lipids and nucleic acids
Autotroph an organism that uses CO2 (an inorganic gas) as its
carbon sourcenot dependent on other living things
Important Mineral Ions Potassium Sodium Calcium
Important Mineral Ions Magnesium Iron
Growth Factors organic compounds that
cannot be synthesized by an organism & must be provided as a nutrient essential amino acids,
vitamins
Nutritional types Chemo-
Chemical compounds Photo-
light
Carbon source
Energy source
photoautotrophs CO2 sunlight
chemoautotrophs CO2 Simple inorganic chemicals
photoheterotrophs organic sunlight
chemoheterotrophs organic Metabolizing organic cmpds
Environmental Influences on Microbial Growth
1. temperature 2. oxygen requirements 3. pH 4. Osmotic pressure 5. UV light 6. Barophiles
1. Temperatures
Minimum temperature lowest temperature that permits a microbe’s growth
and metabolism Maximum temperature
highest temperature that permits a microbe’s growth and metabolism
Optimum temperature promotes the fastest rate of growth and metabolism
Temperature Adaptation Groups
1. Psychrophiles • optimum temperature
below 15oC, capable of growth at 0oC
2. Mesophiles • optimum temperature
20o-40oC, most human pathogens
3. Thermophiles • optimum temperature
greater than 45oC
2. Oxygen Requirements Aerobe
requires oxygen Obligate aerobe
cannot grow without oxygen Facultative anaerobe
capable of growth in the absence OR presence of oxygen
Microaerophile does not grow at normal
atmospheric tensions of oxygen
i.e., the soil, water or the human body
2. Oxygen Requirements
Anaerobe does not require oxygen
Capnophiles Higher CO2
Aerotolerant anaerobes does not utilize oxygen
but can survive and grow to limited extent in its presence
3. pH
The pH Scale Ranges from 0 - 14 pH below 7 is acidic
[H+] > [OH-]
pH above 7 is alkaline [OH-] > [H+]
pH of 7 is neutral [H+] = [OH-]
3. pH
Alkaphiles optimum pH is relatively to
highly acidic Neutrophiles
optimum pH ranges about pH 7 (plus or minus)
Acidophiles optimum pH is relatively to
highly basic
4. Osmotic Pressure Bacteria 80% water Require water to grow Sufficiently hypertonic media at concentrations
greater than those inside the cell (such as 20% sucrose) cause water loss from the cell Osmosis Fluid leaves the bacteria causing the cell to contract
Causes the cell membrane to separate Plasmolysis
Cell shrinkage extreme or obligate halophiles
Adapted to and require high salt concentrations
5. UV Light
Great for killing bacteria Damages the DNA
(making little breaks) in sufficient quantity can kill
the organisms in a lower range causes
mutagenisis Spores tend to be
resistant can survive much longer
exposures
6. Barophiles
Bacteria that grow at moderately high hydrostatic pressures Oceans
Barotolerants Grows at pressures from
100-500 Atm
Barophilic 400-500
Extreme barophilic Higher than 500
Microbial Associations Symbiotic
organisms live in close nutritional relationships; Mutualism
Obligatory Dependent Both members benefit
Commensalism One member benefits Other member not harmed
Parasitism Parasite is dependent and benefits Host is harmed
Microbial Associations
Non-symbiotic organisms are free-livingrelationships not required for survival
Synergism members cooperate and share nutrients
Antagonism some member are inhibited or destroyed by others
Microbial Growth Binary fission:
one cell becomes two
basis for population growth
Process: parent cell enlarges duplicates its
chromosome forms a central
septum divides the cell
into two daughter cells
Population Growth Generation / doubling time
time required for a complete fission cycle Length of the generation time is a measure of the growth
rate of an organism Some bacteria species a population can grow from a
small number of cells to several million in only a few hours!!
Growth Curve Predictable pattern in the population of an organism
over time Four phases:
Lag phase Initial stage with little growth
Exponential growth phase Period of maximum growth Continues as long as cells have adequate nutrients and favorable
environment Stationary phase
Rate of cell growth equals rate of cell death Caused by depleted nutrients and O2, excretion of organic acids and
pollutants Death phase
As limiting factors intensify, cells die exponentially in their own wastes
Growth Curve
Microbial genetics
The DNA Code Nucleic acids are
made of nucleotides each nucleotide
consists of 3 parts:1. a 5 carbon sugar
(deoxyribose or ribose)
2. a phosphate group3. a nitrogenous base
(adenine, thymine, cytosine, guanine, and uracil)
Significance of DNA Structure
1. Maintenance of code during reproduction:
• Constancy of base pairing guarantees that the code will be retained
2. Providing variety: • Order of bases responsible for unique
qualities of each organism
DNA replication is semiconservative because each chromosome ends up with one new strand of DNA and one old strand
Flow of Genetic Information
DNA Recombination Events
Genetic recombination occurs when an organism acquires and
expresses genes that originated in another organism
3 means for genetic recombination in bacteria:
1. Conjugation
2. Transformation
3. Transduction
Transmission of Genetic Material in Bacteria
conjugation requires the attachment of two related species & formation of a bridge that can transport DNA
transformation transfer of naked DNA
transduction DNA transfer mediated by bacterial virus
1. Conjugation
Conjugation transfer of a plasmid or chromosomal
fragment from a donor cell to a recipient cell via a direct connection
Gram positive and gram negative Gram-negative
cell donor has a fertility plasmid (F plasmid, F′ factor) that allows the synthesis of a conjugation (sex) pilus
recipient cell is a related species or genus without a fertility plasmid
donor transfers fertility plasmid to recipient through pilus
F+ and F-
Physical Conjugation
2. Transformation Transformation
chromosome fragments from a lysed cell are accepted by a recipient cell
the genetic code of the DNA fragment is acquired by the recipient
Donor and recipient cells can be unrelated Useful tool in recombinant DNA technology
Insert figure 9.23transformation
3. Transduction Transduction
Bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell
Two types: generalized transduction
random fragments of disintegrating host DNA are picked up by the phage during assembly
any gene can be transmitted this wayspecialized transduction
a highly specific part of the host genome is regularly incorporated into the virus
Generalized Transduction
Specialized Transduction
Transposons Special DNA segments that have the
capability of moving from one location in the genome to another “jumping genes”
Can move from one chromosome site to anotherr chromosome to a plasmid plasmid to a chromosome
May be beneficial or harmful Changes in traits Replacement of damaged DNA Transfer of drug resistance