‘Old’ Eubacteria

Blessing Chirenje

Alice Wagner

Aquificae• Oldest branch of

Bacteria.• One class, one

order and fiver genera: Aquifex and Hydrogenobacter.

• Oxidize hydrogen, thiosulfate, and sulfur; O2 electron acceptor.

Aquificae

• Thermophilic; associated mainly with hot springs, sulfur pools, thermal ocean vents.

• Chemolithotroph: utilizes carbon dioxide as sole source of carbon; energy from the oxidation of inorganic compounds.

Aquificae

• Gram Negative Rod• Form large cell

aggregates, containing up to about 100 individuals.

• Genus Aquifex grows best at 85°C and can grow at temperatures up to 95°C.

Genome 1/3 of E. coli; reduced metabolic flexibility:cannot grow on sugars, amino acids.

16% of coding sequences similar to archaeal genes.

Aquifex aeolicus

• Thermophilic; optimal growth 80-90°C

• Found in geothermally heated soils and marine sediments.

• Gram Negative Rod• Chemoorganotroph:

depends on organic chemicals for energy and carbon.

Thermotogae

• Cell wrapped in sheathe-like outer membrane (“toga”).

• Anaerobic; reduces cystine and thiosulfate to hydrogen sulfide.

• Metabolize carbohydrates: glucose, sucrose, starch, cellulose

• Functional glycolytic pathway.

Thermotogae

ThermotogaT. subterranea strain SL1 was found in a 70°C deep continental oil reservoir.

T. Maritima consists of one circular chromosome: 1,860,725 bp.

Varying amounts of salt and oxygen tolerance.

81 Aracheal-like genes.* 24%

*Nature 1999, 399 (6734):323-9

Deinococcus-Thermus

•One class, two orders: Deinococcales and Thermales

•Three phylum of which Deinococci is best studied

•Deinococci are spheres or rod-shapped with distinct 16s rRNA

Deinococcus• GPC or GPR ;

resistant to radiation, extreme heat, extreme cold, drying, vacuum of space.

• Breakdown nuclear waste and toxic chemicals.

• Isolated from ground meat, feces, air, fresh water.

• Natural habitat unknown.

Deinococcus• Aerobic, mesophilic

heterotrophs; occur in clouds and rainwater and which can spoil food.

• Highly resistant to gamma and X-rays:– Very efficient DNA repair

system.– D. radiodurans have 4-10

copies of their DNA molecule. Most bacteria have only one copy.

– Megaplasmid and small plasmid chromosomes

Deinococcus• Associated in pairs

or tetrads;• Atypical GP cell

wall periplasmic space has large amounts of palmitoleic acid.

• D. radiodurans: radiation 1000X greater than would kill a human.

• Latin: "strange berry that withstands radiation.

Thermus thermophilus

• Thermophilic heterotrophs found in warm water environments especially hot springs.

• Source of Taq polymerase used in the PCR:– enables DNA to

be replicated in large quantities. 

Thermus thermophilus

• Gram-negative bacteria.• Optimal growth

temperature of 48°C and 85°C

• Ribosomes and ribosomal subunits do not disintegrate when kept for longer periods at 20°C'

• “Down-temperature” evolution*

• Crystal structure of homoisocitrate dehydrogenase

*1999, University of Wisconsin, Board of Regents.

'Cell 102: 615-623 (2000)

Chlamydia• The phylum

Chlamydiae has one class, one order, four families and six genera.

• They evloved about 2 billion years ago.

• Nonmotile, coccoid, gram-neagtive.

• One of the smallest of all bacteria; ~ 500 nm in width, not much bigger than the largest viruses.

Chlamydia

•Obligate Intracellular bacteria with a unique developmental cycle involving elementary bodies (EBs).•Elementary bodies reorganize into reproductively specialized reticulate bodies (RBs) which then change back to infectious elemenatry bodies.•Completely dependent on the host for ATP.

Chlamydia• Gram-negative-like

wall but lacks muramic acid and peptidoglycan

• Use cross-linking of outer membrane and, possibly, periplasmic proteins to achieve osmotic stability

• Found mostly in mammals and birds but have been recently isolated from spiders, clams and freshwater invertebrates

ChlamydiaThree recognized human

pathogens– C. trachomatis - causes

chlamydia, a sexually transmitted disease, trachoma, an eye infection that is a frequent cause of blindness and other human diseases.

– C. psittaci- causes psittacosis in humans and infects many other mammals as well.

– C. pneumoniae - a causative agent of human pneumonia

Spirochetes• The phylum has one

class, Spirochaetes, three families, and 13 genera.

• Gram-negative, chemoheterotrophic; long flexibly helical coiled bacteria.

• Most are free-living and anaerobic, but can be symbiotic, or parasitic.

• Distinguished by the presence of flagella running lengthwise between the cell membrane and cell wall, called axial filaments

• The axial filament (a complex of periplasmic flagella) lies in a flexible outer sheath (outer membrane) outside the protoplasmic cylinder that houses the nucleoid and cytoplasm; the function of the sheath is essential, but unknown.

• Flagellar rotation is responsible for motility by an unknown mechnism presumably by rotating the outer sheath or flexing the cell for a crawling motion.

• Spirochete can move through very viscous solutions though they lack external rotating flagella.

Spirochetes

Spirochetes• Exceptionally diverse ecologically and grow in

habitats ranging from mud to the human mouth.• Ecologically diverse:

– Spirochaeta are free-living, and grow in anaerobic and sulfide-rich fresh water and marine environments.

– Leptospira is both pathogenic and saprophytic, can occupy diverse environments, habitats and life cycles.

– Treponema includes the caustive agent of syphillis (T. pallidum)

– Borrelia includes the caustive agent of Lyme disease (B. burgdorferi)