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