Phylogeny of bacteria

Nonproteobacteria gram-negative bacteria

Many gram-negative bacteria belong to diverse phyla which differ from the proteobacteria

Some belong to the oldest branches of bacteria while others have arisen more recently

Aquificae and Thermotogae

The two oldest branches of bacteria

Both are hyperthermophilic

Deinococcus-Thermus

Species belonging to the genus Deinococcus are best studied

Very resistant to radiation and desiccation

T. aquaticus Taq polymerase

Deinococcus

Often associate in pairs and tetrads

Stain gram + although cell wall is similar to gram cells

Photosynthetic nonproteobacteria

Photosynthetic nonproteobacteria

Phylum Chloroflexi

Also contains nonphotosynthetic bacteria

Are the green nonsulfur bacteria

Can be isolated from neutral to alkaline hot springs

Photosynthetic nonproteobacteria

Phylum Chlorobi

Composed of 1 class, 1 order and 1 family

Are the green sulfur bacteria

Use sulfur and sulfur-containing compounds as electron sources

Photosynthetic nonproteobacteria

Phylum Cyanobacteria

Largest and most diverse group of photosynthetic bacteria

Photosynthetic system resembles that of eukaryotes

Employ a variety of reproductive mechanisms (e.g. binary fission, multiple fission, budding andfragmentation)

Photosynthetic nonproteobacteria

Phylum Cyanobacteria

Vary greatly in shape and appearance

Phylum Planctomycetes

Spherical or oval bacteria that lack peptidoglycan

Reproduce by budding

In some species the nuclear body is membrane-bound

Phylum Chlamydiae

Originally grouped with the rickettsias (rickettsias now in -proteobacteria)

Both are small obligate intracellular parasites

Genus Chlamydia is the best studied

Phylum Chlamydiae

Three species are important human pathogens

Cell walls lack peptidoglycan

Osmotic stability achieved by cross-linking of outer membrane proteins with disulfide bonds

Chlamydial life cycle

Phylum Spirochaetes

Distinguished by their structure and mechanism of motility

Slender long bacteria with a helical shape

Many are too thin to be seen using phase-contrast or dark-field microscopy

Phylum Spirochaetes

Phylum Spirochaetes

Ecologically diverse

Some are free-living (soil and freshwater)

Others live in symbiotic relationships with other organisms (insects, mollusks and mammals)

Phylum Spirochaetes

Phylum Spirochaetes

Some species are human pathogens

e.g. Treponema pallidum (Syphilis)

Borrelia burgdorferi (Lyme disease)

Phylum Spirochaetes

Cells are bound by flagella called endoflagella (or axial fimbrils or periplasmic flagella)

Complex of flagella called axial filaments

Filaments bound by a sheath

Phylum Spirochaetes

Motility likely due to rotation of filaments

Rotation causes corkscrew-like movement of the cell

Phylum Bacteroidetes

Very diverse phylum

Closely related to Chlorobi

Anaerobic rods of various shapes

Phylum Bacteroidetes

Phylum Bacteroidetes

Grow in the oral cavities and intestinal tracts of animals

They are often beneficial to their host

B. fragilis is the cause of anaerobic infections in humans