This chapter is devoted to nine of the more interesting and important eubacterial groups from volumes 1 and 5 of the 2^nd edition of Bergey's Manual of Systematic Bacteriology. Though the organization and perspective of the 2^nd edition is used, the description of each group in the current edition is summarized. Where appropriate the distinguishing characteristics, morphology, reproduction, physiology, metabolism, and ecology of each group is included. The taxonomy of each major group is summarized and representative species are discussed.

After reading this chapter you should be able to:

• discuss the deeply branching eubacterial groups represented by the hyperthermophiles Aquifex and Thermotoga
• discuss the gram-positive deinococci
• discuss the photosynthetic bacteria that are described in volume 1 of the 2^nd edition of Bergey's Manual
• discuss the chlamydiae and their loss of some of their metabolic independence, thereby becoming dependent on their host for their energy supply and for certain cellular constituents
• discuss gliding motility and its usefulness for organisms that digest insoluble nutrients or that move over the surfaces of solid substrata

1. Aquifex and Thermotogas

1. Aquifex (e.g., Aquifex pyrophilus) and its relatives such as Hydrogenobacter are members of

II. The Deinococci

1. One familywith three genera
2. Spherical or rod-shaped with distinctively different 16S rRNA
3. Associated in pairs or tetrads
4. Aerobic, mesophilic, catalase positive, and usually able to produce acid from few sugars
5. They stain gram-positive but have a layered cell wall and an outer membrane like the gram-negative bacteria
6. They have L-ornithine in their peptidoglycan; lack teichoic acid; have a plasma membrane with large amounts of palmitoleic acid rather than phosphatidylglycerol phospholipids
7. Extraordinarily resistant to desiccation and radiation: can survive 3-5 million rad whereas 100 rad can be lethal to humans
8. Can be isolated from ground meat, feces, air, fresh water, and other sources but their natural habitat is not known
9. Have an unusual ability to repair chromosomal damage (even fragmentation) that probably accounts for their ability to resist radiation

3. Photosynthetic Bacteria

1. Three groups: purple bacteria, green bacteria, and cyanobacteria
2. Green and purple bacteria use anoxygenic photosynthesis

1. Use bacteriochlorophylls
2. Use H₂O and other reduced electron donors
3. Use wavelengths of light that enable them to grow at deeper water levels

1. Use chlorophyll a
2. Use H₂O as an electron donor
3. Grow primarily at the surface of bodies of water

1. Has both photosynthetic and nonphotosynthetic members
2. Chloroflexus is the major representative of the photosynthetic green nonsulfur bacteria

1. Filamentous, gliding, thermophilic bacteria
2. Often isolated from neutral to alkaline hot springs
3. Grows in the form of orange-reddish mats
4. Metabolism is similar to that of the purple nonsulfur bacteria
5. Can carry out anoxygenic photosynthesis with organic compounds as carbon sources or can grow aerobically as a chemoheterotroph
6. Not closely related to any eubacterial group

1. Green sulfur bacteria
2. Obilgately anaerobic photolithoautotrophs that use hydrogen sulfide, elemental sulfur and hydrogen as electron sources
3. Elemental sulfur produced by sulfide oxidation is deposited outside the cell
4. Photosynthetic pigments are located in a ellipsoidal vesicles called chlorosomes (chlorobium vesicles) which are attached to the plasma membrane but not continuous with it
5. Chlorosome membrane is not a normal lipid bilayer
6. Chlorosomes have accessory bacteriochlorophylls but the reaction center bacteriochlorophyll is located in the plasma membrane
7. They lack flagella and are nonmotile but some species have gas vesicles to adjust their depth for adequate light and hydrogen sulfide; species without gas vesicles are found in sulfide-rich muds at the bottom of lakes and ponds
8. Morphologically diverse; rods cocci, or vibrios; grow singly, in chains, or in clusters; grass-green or chocolate-brown in color

1. The cyanobacteria are the largest and most diverse group of photosynthetic bacteria
2. The 1^st edition of Bergey's Manual describes 34 genera in some detail
3. Procaryotes but the photosynthetic system resembles that of eucaryotes

1. They have chlorophyll a and photosystem II
2. Carry out oxygenic photosynthesis

1. Similar to, but different from, cyanobacteria
2. Three recognized genera

3. The Planctomycetes

1. Order Planctomycetales

1. Spherical or oval, budding eubacteria with distinctive crateriform structures (pits) in their

walls

2. In two genera, Gemmata and Pirullela, the nuclear body is membrane bounded,

1. Nonmotile, coccoid, gram-negative eubacteria
2. Obligate intracellular parasites with a unique developmental cycle involving elementary bodies (EBs) that reorganize into reproductively specialized reticulate bodies (RBs) which then change back to infectious elementary bodies
3. Completely dependent on the host for ATP; most metabolic activity in RBs; very little metabolic activity in EBs
4. Gram-negative-like wall but lacks muramic acid and peptidoglycan
5. Use cross-linking of outer membrane and, possibly, periplasmic proteins to achieve osmotic stability
6. Found mostly in mammals and birds but have been recently isolated from spiders, clams and freshwater invertebrates
7. Three recognized human pathogens

1. C. trachomatis - trachoma, nongonococcal urethritis, and other diseases in humans

and mice

2. 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

3. C. pneumoniae - a causative agent of human pneumonia

3. The Spirochetes

1. Gram-negative, chemoheterotrophic, flexibly helical bacteria that exhibit a creeping

(crawling) motility due to a structure called an axial filament

2. 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 (spirochetes will die if it is removed) but unknown

3. Flagellar rotation is responsible for motility by an unknown mechanism presumably by

rotating the outer sheath or flexing the cell for a crawling motion

4. Can be anaerobic, facultatively anaerobic, or aerobic and can use a diverse array of organic

molecules as carbon and energy sources

5. Ecologically diverse

1. Spirochaeta - anaerobic
2. Leptospira - aerobic
3. Treponema - includes the causative agent of syphillis (T. pallidum)
4. Borrelia - includes the causative agent of Lyme disease (B. burgdorferi)

1. Obligate anaerobes, nonsporing, chemoheterotrophic
2. Found in oral cavity and intestinal tract of humans and other animals and the rumen of ruminants
3. Often benefit the host by degrading cellulose, pectins, and other complex carbohydrates, providing extra nutrition for the host
4. Can constitute as much as 30% of the bacteria isolated from human feces
5. Some species can be associated with disease

1. Differ in morphology, life cycle and physiology
2. Cytophaga - slender rods with pointed ends
3. Sporocytophaga - similar to Cytophaga but form spherical resting cells called microcysts
4. Flexibacter - form long threads; unlike the other two genera, they are unable to degrade complex carbohydrates

1. Gliding motility used when in contact with a surface; leaves a slime trail; bacteria are

nonmotile when in suspension

2. Many are capable of utilizing insoluble material as nutrient sources, encountering them during

their gliding activity

3. Can position themselves for optimal conditions of light intensity, oxygen, hydrogen sulfide,

temperature, and other factors that influence growth

4. Play a major role in the mineralization of organic matter and can damage exposed wooden

structures

5. Contribute significantly to wastewater treatment
6. Some pathogenic species (e.g., C. columnaris causes disease in freshwater and marine fish)