Prokaryotic - 0.2-2 x 0.2-50 µm (typically, ~1
µm x 1-5 µm)
Cell wall
protects the cytoplasm from osmotic pressure
changes and provides cell shape - bacillus
(cylindrical rod); coccus (spherical); coccobacillus
(pleomorphic); spiral (helical); or amorphous (no cell
wall)
contains peptidoglycan and may contain:
Gram-positive - teichoic acid, various other
polysaccharides and/or proteins and/or lipids
Gram-negative - outer membrane composed of
lipid bilayer containing lipopolysaccharide (LPS or
endotoxin) and various proteins
Membranes - glycerol-based phospholipids with ester
linkages which form typical bilayer membranes
Ribosomes - small RNA/protein particles which are
required for protein synthesis
Chromosome - single molecule of double-stranded DNA
(4700 kbp for Escherichia coli) that contains the "blueprint"
for all cell structure and activity in regions called
genes
Plasmids - some have pieces of extrachromosomal DNA
(generally circular) that contain only a few genes, but can
replicate themselves and are exchanged among various species of
bacteria
Endospore - thick-walled structures that are highly
resistant to adverse environmental conditions (high
temperature, drying, oxygen, etc.); generally formed only by
bacilli, and then each cell only forms one
Capsules - polysaccharide "coatings" secreted by
cells (act as anchors)
Flagella - long, thin protein (flagellin) polymers
that provide motility
Pili - long, thin protein (pilin) polymers that act
as cell "anchors" and may mediate plasmid transfer
Genetics
Gene exchange - mediated by plasmids via
conjugation, transduction or transformation
Operons - these coordinately-controlled groups of
genes use typical on/off signals (TATA box, Pribnow box,
Shine-Dalgarno sequence, etc.)
Reproduction - asexual, by
binary fission (dividing into two roughly equivalent-sized
daughter cells); called "budding" when daughter cells are unequal
in size
pH - most "prefer" pH 5-8, but some thrive at pH
as low as 3 or as high as 10
salts - some are halophilic (require high salt
concentration for growth)
Absorptive nutrition - versatile, although some
require growth factors
organotrophic
- derive energy and carbon from catabolism of organic
molecules
lithotrophic
- derive energy and carbon from catabolism of inorganic
molecules
phototrophic
- derive energy from sunlight and carbon from inorganic
molecules (typically carbon dioxide)
Metabolism - is highly adaptable due largely to use
of inducible genes (especially those in operons) and efficient
feedback control systems for both catabolic and anabolic
pathways
Tricarboxylic acid (TCA) or Kreb's cycle and electron
transport system (ETS) present in respiratory members;
many other (sometimes highly specialized) catabolic pathways
are also found
ATP synthesis via:
chemiosmotic mechanisms - utilize proton
gradient and membrane-bound ATP synthase for
phosphorylation via photosynthesis or respiration - some
use final electron acceptors other than oxygen (nitrate,
sulfate, etc.)
substrate-level phosphorylation - all use this
to some extent; fermenters use it exclusively
Habitat - ubiquitous (found
essentially everywhere ... different bacteria are able to grow in
many different environments, from benign and hospitable to extreme
ones)
Importance
Source of reduced carbon - lithotrophs
and phototrophs
generate basic nutrients for smallest animals
Saprophytic, parasitic - organotrophs
are generally decomposers, but some are pathogenic
Symbiotic - many interact with other organisms; some
bacteria are endosymbionts
Prokaryotic - 0.1-15 x 0.1-200 µm (typically,
0.3-1 x 0.3-6 µm)
Membranes - structure similar to that found in
Bacteria and Eukarya, but Archaea use ether linkages in
lipids (rather than ester linkages) and form:
bilayer membranes from glycerol-diethers
monolayer membranes from diglycerol-tetraethers (thermal
stability?)
Cell wall
protects the cytoplasm from osmotic pressure changes and
provides cell shape - bacillus; coccus; lobed or irregular
spheres (no cell wall)
Gram-positive or Gram-negative, lacks
peptidoglycan (no muramic acid or D-amino acids);
instead, possess:
pseudopeptidoglycan - alternating repeats of
N-acetylglucosamine and N-acetyltalosaminuronic acid (1-3
links, lysozyme resistant) with 7-member L-amino acid
cross-links (Methanobacterium)
polysaccharide - thick polymers containing
galactosamine, glucuronic acid, glucose and acetate
(Methanobacterium) or sulfated glucose,
glucoseamine, mannose, mannoseamine, galactose and
galactosamine (Halococcus)
glycoprotein - negatively charged proteins
with many acidic residues (especially aspartic acid)
"decorated" with polymers of glucose, glucoseamine,
mannose, galactose, ribose and arabinose (extreme
halophiles, Halobacterium; extreme thermopliles,
Sulfolobus, Pyrodictium)
protein - single polypeptide subunit that
forms a sheath (Methanospirillum) or several
distinct polypeptide subunits (Methanococcus,
Methanomicrobium)
Ribosomes - small RNA/protein particles which are
required for protein synthesis (act more like those of Eukarya
(sensitive to anisomysin, insensitive to chloramphenicol and
kanamycin) than those of Bacteria, even though they are 70S);
EF-2 is sensitive to diphtheria toxin
Chromosome - single (closed circular) molecule of
double-stranded DNA (one-third to one-half as much DNA per cell
as found in bacteria such as E. coli)
Plasmids - these pieces of extrachromosomal DNA may
make up as much as 25-30% of cellular DNA
Capsules - polysaccharide "coatings" secreted by
cells (???)
Flagella - long, thin protein (flagellin) polymers
that provide motility
Pili - not formed (???)
Genetics
Gene exchange - mediated by plasmids via
transduction (conjugation? or transformation?)
Operons - probably present, since Archaea have
polycistronic mRNA; these coordinately controlled groups of
genes use typical on/off signals (TATA box, Pribnow box,
Shine-Dalgarno sequence, etc.)
Introns - like those found in Eukarya (none are
found in Bacteria)
RNA polymerases behave more like those of Eukarya
(large, complex, resistant to rifampin)
Reproduction - asexual, via
binary fission, budding, fragmentation
Physiology
Physical requirements
temperature - most are thermophiles, some are extreme
thermophiles
salts - some extreme halophiles (require high salt
concentration for growth)
Absorptive nutrition - some require growth factors
organotrophic - most are strict aerobes which
derive energy from catabolism of organic molecules
lithotrophic - anaerobes which derive energy and
carbon from methanogenesis
phototrophic - some Halobacterium species
synthesize ATP using a bacteriorhodopsin
system (not photosynthesis)
Metabolism - varies greatly among groups
TCA cycle and electron transport system
(ETS) - fairly typical in halophiles and
thermophiles, but not in methanogens
ATP synthesis via:
chemiosmotic mechanisms - proton gradient and
membrane-bound ATP synthase utilized for phosphorylation;
some use final electron acceptors other than oxygen
(nitrate, oxidized sulfur etc.)
substrate-level phosphorylation - all
organotrophs use it some
Habitat - generally in extreme
habitats (swamps, salt lakes, acidic hot springs)
Extreme thermophiles
(Thermoplasma, Sulfolobus) are sulfur-dependent
acidophiles with temperature optima of greater than 50C
(extreme thermophiles prefer temperatures greater than
70C)
Extreme halophiles (Halobacterium,
Halococcus) require high salt for growth
Methanogens are generally found in anaerobic
environments rich in organic matter
Importance
Reduced carbon source - lithotrophs and phototrophs
generate basic nutrients for smallest animals
Symbionts - e.g., rumen of cattle, etc.
Saprophytic - organotrophs are generally
decomposers
eukaryotic - individual cells are generally larger
than bacterial cells
dimorphic - some are unicellular
(yeasts), but most are mycelial (moulds) which
have a multicellular mycelium that is a mesh of elongated
filamentous hyphae that are frequently branched, with
perforated septa between cells to ensure unimpeded movement of
nutrients from one region of the mycelium to another
chitin in cell walls of most, but some contain
cellulose instead
Genetics
gene exchange - recombination during meiosis
generates diversity
introns and exons are present in fungi, as they are
in the typical eukaryote
Reproduction - generally via
modified hyphae that form reproductive spores
sexual - fusion of haploid nuclei leading to
formation of spores
asexual
binary fission
budding - unequal binary fission
fragmentation of hyphal elements
arthrospores formed directly from hyphal
fragmentation
chlaymdospores formed from directly hyphal
fragmentation, but surrounded by a thick wall
spores - thick walls help them withstand dry,
cold, low-nutrient conditions
sporangiospores - produced inside a
sporangium
conidiospores - produced "naked" in "rows" on
conidiophores
blastospores - spores produced directly from
"mother" cell by budding
Physiology
aerobic (some facultatively anaerobic, but none are
anaerobic) organotrophs
absorptive nutrition - extracellular digestion using
secreted enzymes
most are mesophilic (20-35C optima); some are
psychrophilic, some are mildly thermophilic
pH optimum near 5.5, but some grow at extremes of
the pH range 2-9
Habitat - generally prefer dark,
moist habitats containing organic material
terrestrial or aquatic (some live in freshwater,
others in marine, habitats)
symbiotes with plants (mycorrhizae) or algae
or cyanobacteria (lichens)
Importance
most saprophytic (decomposers); some are pathogenic
for plants or animals
some are symbiotic, especially those that are the
fungal component of lichens
commercially important in food production and
spoilage, as well as pharmaceutical and industrual chemical
production
