Aquificae-thought to represent the deepest (oldest) branch of bacteria;
two of its best studies genera are Aquifex and Hydrogenobacter
Hyperthermophilic
Chemolithoautotrophic-generate energy by oxidizing electron donors
such as hydrogen, thiosulfate, and sulfur with oxygen as the electron
acceptor
Thermotogae-second deepest branch of the bacteria; best studies are members
of the genus Thermotoga
Hyperthermophiles with an optimum of 80°C and a maximum of 90°C
Gram-negative rods with an outer sheath-like envelope (like a toga)
that can balloon out from the ends of the cell
Grow in active geothermal areas (e.g., marine hydrothermal vents and
terrestrial solfataric springs)
Chemoheterotrophs with a functional glycolytic pathway; can grow anaerobically
on carbohydrates and protein digests
Deinococcus-Thermus
Consists of three genera; genus Deinococcus is the best studied
Spherical or rod-shaped; often associated in pairs or tetrads
Aerobic, mesophilic, catalase positive, and usually able to produce
acid from only a few sugars
They stain gram-positive but have a layered cell wall and an outer
membrane like gram-negative bacteria; have L-ornithine in their peptidoglycan
and lack teichoic acid
Have a plasma membrane with large amounts of palmitoleic acid rather
than phosphatidylglycerol phospholipids
Extraordinarily resistant to desiccation and radiation
Relatively little is known about the biology of deinococci
Can be isolated from ground meat, feces, air, fresh water, and other
sources but their natural habitat is not known
Genome consists of two circular chromosomes, a mega plasmid, and a
small plasmid
Have an unusual ability to repair chromosomal damage (even fragmentation)
and this probably accounts for their ability to resist desiccation and
radiation; genomic analysis show they have many DNA repair genes and many
repeat sequences
Photosynthetic Bacteria
Three groups: purple bacteria, green bacteria, and cyanobacteria
Cyanobacteria carry out oxygenic photosynthesis, using water as an
electron source for the generation of NADH and NADPH 2. Green and purple
bacteria carry out anoxygenic photosynthesis, using reduced molecules
other than water, as an electron source for the generation of NADH and
NADPH
Purple sulfur bacteria use reduced sulfur compounds as electron
sources and accumulate sulfur granules within their cells
Green sulfur bacteria use reduced sulfur compounds as electron
sources and deposit sulfur granules outside their cells
Purple nonsulfur bacteria use organic molecules as their electron
sourcec
Type of photosynthetic pigments and oxygen relationships correlates with
ecological distribution
Purple and green bacteria are anaerobes and use bacteriochlorophyll
pigments
Grow better in deeper, anaerobic zones of aquatic habitats
Their bacteriochlorophylls absorb shorter wavelengths of light,
which penetrate to these deeper zones
Cyanobacteria have chlorophyll a, which absorbs longer wavelengths
of light; these bacteria are found primarily at the surface of bodies
of water
The 2nd edition of Bergey’s Manual divides the photosynthetic bacteria
into six groups:
Phylum Chloroflexi-green nonsulfur bacteria
Phylum Chlorobi-green sulfur bacteria
Phylum Cyanobacteria
Phylum Proteobacteria-Purple sulfur bacteria (gammaproteobacteria)
and purple nonsulfur bacteria (alphaproteobacteria and betaproteobacteria);
these organisms are covered in chapter 22
Phylum Chloroflexi-green nonsulfur bacteria
Genus Chloroflexus-major representative of the photosynthetic green
nonsulfur bacteria
Filamentous, gliding bacteria
Thermophilic, often isolated from neutral to alkaline hot springs
where they grow in the form of orange-reddish mats
Ultrastructure and photosynthetic pigments are like green bacteria,
but their metabolism is similar to that of the purple nonsulfur
bacteria
Can carry out anoxygenic photosynthesis with organic compounds
as carbon sources or can grow aerobically as a chemoheterotroph
Genus Herpetosiphon-represents nonphotosynthetic members of phylum
Chloroflexi; contains gliding, rod-shaped filamentous bacteria; aerobic
chemoorganotrophs with respiratory metabolism; isolated from fresh water
and soil
Chlorobia-green sulfur bacteria
Obligately anaerobic photolithoautotrophs that use hydrogen sulfide,
elemental sulfur and hydrogen as electron sources; elemental sulfur
produced by sulfide oxidation is deposited outside the cell
Photosynthetic pigments are located in ellipsoidal vesicles called
chlorosomes, which are attached to the plasma membrane but not continuous
with it; chlorosome membrane is not a normal lipid bilayer; chlorosomes
have accessory bacteriochlorophylls but the reaction center bacteriochlorophyll
is located in the plasma membrane
Lack flagella and are nonmotile; some species have gas vesicles to
adjust their depth in water for adequate light and hydrogen sulfide;
species without gas vesicles are found in sulfide-rich mud at the bottom
of lakes and ponds.
Morphologically diverse (rods, cocci, or vibrios; grow singly, in
chains, or in clusters); grass green or chocolate-brown in color
Phylum Cyanobacteria
Largest and most diverse group of photosynthetic bacteria (56 genera
are described in the 2nd edition of Bergey’s Manual)
Photosynthetic system resembles that of eucaryotes, having chlorophyll
a and photosystem II; carry out oxygenic photosynthesis
Photosynthetic pigments are in thylakoid membranes lined with
particles called phycobilisomes (contain phycobilin pigments), which
transfer energy to photosystem II; some species are red-brown and
contain the pigment phycoerythrin
Fix carbon dioxide by the Calvin cycle
Do not have functional TCA cycle; pentose phosphate pathway plays
a central role in their metabolism
Although they are oxygenic photolithoautotrophs, some can grow
slowly in the dark as chemoheterotrophs, and some species can carry
out anoxygenic photosynthesis if in an anaerobic environment
Vary greatly in shape and appearance
May be unicellular, exist as colonies of many shapes, or form
filaments called trichomes (rows of bacterial cells that are in
close contact with one another over a large area)
Have typical procaryotic structures with a gram-negative cell
wall
Often use gas vesicles to move vertically in the water; many
filamentous cyanobacteria have a gliding motility; although cyanobacteria
lack flagella, some marine species are able to move by an unknown
mechanism
Reproduce by binary fission, budding, fragmentation, and multiple
fission
Fragmentation generates small motile filaments called hormogonia
Some species develop akinetes, which are thick-walled resting
cells that are resistant to desiccation; these often germinate to
form new filaments
Many filamentous cyanobacteria fix atmospheric nitrogen in special
cells (heterocysts), which protect the oxygen-sensitive nitrogenase;
other cyanobacteria that lack heterocysts can also fix nitrogen
Taxonomy of cyanobacteria is unsettled; the 2nd edition of Bergey’s
Manual divides them into five subsections
The prochlorophytes, which used to be categorized separately
from other cyanobacteria, are now dispersed into subsections I and
III
Prochlorophytes differ from other cyanobacteria by having chlorophyll
b as well as chlorophyll a and by lacking phycobilisomes
The three recognized prochlorophyte genera are quite different from
one another
Prochloron-extracellular symbiont on the surface or within the
cloacal cavity of marine colonial ascidan invertebrates
Prochlorothrix-free living
Prochlorococcus-has a modified chlorophyll a and a-carotene rather
than b-carotene
The five subsections differ markedly in terms of morphology and reproduction
Subsection I-unicellular rods or cocci; most are nonmotile; reproduce
by binary fission or budding
Subsection II-unicellular, though some may be held together in
an aggregate by an outer wall; reproduce by multiple fission to
form baeocytes
Subsections III, IV, and V-filamentous cyanobacteria
Tolerant of environmental extremes; thermophilic species can grow
at temperatures up to 75°C
Successful at establishing symbiotic relationships (e.g., in lichens;
symbionts with protozoa, fungi and plants)
Phylum Planctomycetes
Contains one class, one order, and four genera
Spherical or oval, budding bacteria with distinctive crateriform structures
(pits) in their walls
In two genera, Gemmata and Pirullela, the nuclear body is membrane bounded,
something that is not seen in other procaryotes
The genus Planctomyces attaches to surfaces through a stalk and holdfast;
other genera lack stalks
Most have life cycles in which sessile cells bud to produce motile swarmer
cells
Phylum Chlamydiae
This phylum has only 5 genera; Chlamydia is the most important and best-studied
genus
Nonmotile, coccoid, gram-negative bacteria
Reproduce within cytoplasmic vesicles of host cells by a unique developmental
cycle involving elementary bodies (EBs) and reticulate bodies (RBs)
Gram-negative-like wall but lacks muramic acid and peptidoglycan;
EBs use cross-linking of outer membrane proteins, and possibly, periplasmic
proteins to achieve osmotic stability
Obligately intracellular parasites; found mostly in mammals and birds
but have been recently isolated from spiders, clams, and freshwater
invertebrates
Have one of the smallest procaryotic genomes
Chlamydial reproduction
Begins with attachment of an EB to host cell
Host cell phagocytizes the EB, but fusion of lysosome with the phagosome
is prevented by the EB
EB reorganizes itself into a reticulate body (RB), which is specialized
for reproduction
RB reproduces repeatedly, giving rise to many RBs, all within a vacuole
RBs change back into EBs, and these are released when the host lyses
Chlamydial metabolism
Usually thought of as being completely dependent on host for ATP; however,
recent genomic analysis indicates that some genes for ATP synthesis are
present in the genome
RBs have a number of biosynthetic capabilities (e.g., DNA, RNA, glycogen,
lipid, protein, some amino acids and coenzymes)
EBs have very little metabolic activity; seem to be dormant forms concerned
exclusively with transmission and infection
Three recognized human pathogens
C. trachomatis-trachoma, nongonococcal urethritis, and other diseases
in humans and mice
C. psittaci-causes psittacosis in humans and infects many other mammals
as well; invades the respiratory and genital tracts, the placenta, developing
fetuses, the eye, and synovial fluid of the joints
C. pneumoniae-a causative agent of human pneumonia and possibly atherosclerosis
and heart disease
Phylum Spirochaetes
Gram-negative, chemoheterotrophic, flexibly helical bacteria that exhibit
a creeping (crawling) motility due to a structure called an axial filament
The axial filament (a complex of periplasmic flagella) lies in a flexible
outer sheath (outer membrane) outside the protoplasmic cylinder, which houses
the nucleoid and cytoplasm; function of the sheath is essential (spirochetes
will die if it is removed) but unknown
Flagellar rotation is responsible for motility by an unknown mechanism,
presumably by rotating the outer sheath or flexing the cell for a crawling
motion.
Can be anaerobic, facultatively anaerobic, or aerobic and can use a diverse
array of organic molecules as carbon and energy sources
Ecologically diverse
Spirochaeta-free-living and often found in anaerobic, sulfide-rich
aquatic environments
Leptospira-aerobic water and moist soils
Many, including Criptispira and Treponema form symbiotic associations
with other organisms
Some members of Treponema, Borrelia, and Leptospira cause disease
(e.g., T. pallidum is the causative agent of syphilis, and B. burgdorferi
is the causative agent of Lyme disease)
Phylum Bacteroidetes
Consists of 50 genera divided into 3 classes (Bacteroides, Flavobacteria,
and Shpingobacteria)
Found in oral cavity and intestinal tract of humans and other animals
and the rumen of ruminants where they often benefit the host by degrading
cellulose, pectins, and other complex carbohydrates, thereby providing
extra nutrition for the host
Some species can be associated with disease
Class Sphingobacteria
Often have sphinolipids in their cell walls
Contains several genera including Flexibacter, Cytophaga and Sporocytophaga;
differ in morphology, life cycle and physiology
Cytophaga-slender rods with pointed ends
Sporocytophaga-similar to Cytophaga but form spherical resting
cells called microcysts
Flexibacter-form long threads; unlike the other two genera, they
are unable to degrade complex carbohydrates
Physiology (as seen in the genera Cytophaga and Sporocytophaga)
Aerobes that actively degrade complex carbohydrates (e.g., cellulose,
chitin, keratin)
Play a major role in the mineralization of organic matter and
can damage exposed wooden structures
Contribute significantly to wastewater treatment
Most cytophagas are free-living, but some pathogenic species are
known (e.g., C. columnaris causes disease in freshwater and marine fish)
Are nonmotile when in suspension, but exhibit gliding motility when
in contact with a surface; leaves a slime trail;
Gliding motility has advantages
Enables them to find and digest insoluble material encountered
as they move
Allows motility in drier habitats
Enables them to position themselves for optimal environmental
conditions
