Classification of bacteria part 2

Gram-Negative Eubacteria that Have Cell Walls
This is a heterogeneous group of bacteria that have a complex (gram-negative type) cell envelope consisting of an outer membrane, an inner, thin peptidoglycan layer (which contains muramic acid and is present in all but a few organisms that have lost this portion of the cell envelope), and a cytoplasmic membrane. The cell shape may be spherical, oval, straight or curved rods, helical, or filamentous; some of these forms may be sheathed or encapsulated. Reproduction is by binary fission, but some groups reproduce by budding. Fruiting bodies and myxospores may be formed by the myxobacteria. Motility, if present, occurs by means of flagella or by gliding. Members of this category may be phototrophic or nonphototrophic bacteria and include aerobic, anaerobic, facultatively anaerobic, and microaerophilic species; some members are obligate intracellular parasites.

Gram-Positive Eubacteria that Have Cell Walls
These bacteria have a cell wall profile of the gram-positive type; cells generally, stain gram-positive. Cells may be spherical, rods, or filaments the rods and filaments may be nonbranching, or may show true branching. Reproduction is generally by binary fission. Some bacteria in this category produce spores as resting forms (endospores). These organisms are generally chemosynthetic heterotrophs and include aerobic, anaerobic, and facultatively anaerobic species. The groups within this category include simple asporogenous and sporogenous bacteria as well as the structurally complex actinomycetes and their relatives.

Eubacteria Lacking Cell Walls
These are microorganisms that lack cell walls (commonly called mycoplasmas and comprising the class Mollicutes) and do not synthesize the precursors of peptidoglycan. They are enclosed by a unit membrane, the plasma membrane They resemble the L forms that can be generated from many species of bacteria (notably gram-positive eubacteria); unlike L forms, however, mycoplasmas never revert to the walled state, and there are no antigenic relationships between mycoplasmas and eubacterial L forms.

The Archaebacteria
These prokaryotic organisms are predominantly inhabitants of extreme terrestrial and aquatic environments (high salt, high temperature, anaerobic); some are symbionts in the digestive tract of animals. The archaebacteria consist of aerobic, anaerobic, and facultatively anaerobic organisms that are chemolithotrophs, heterotrophs, or facultative heterotrophs .Some species are mesophiles, while other are capable of growing at temperatures above 100 °C. These hyperthermophilic archaebacteria are uniquely adapted for growth and multiplication at high temperatures. With few exceptions enzymes isolated from these organism are intrinsically more thermostable than their counterparts from mesophilic organisms. Some of these thermostable enzymes, such as the DNA polymerase from Thermus aquaticus (Taq polymerase), are important components of DNA amplification methods such as the polymerase chain reaction (PCR). Archaebacteria can be distinguished from eubacteria in part by their lack of peptidoglycan cell wall, possession of isoprenoid diether or diglycerol tetraether lipids, and characteristic ribosomal RNA sequences. Archaebacteria also share some molecular features with eukaryotes Cells may have a diversity of shapes, including spherical, spiral, and plate- or rod-shaped; unicellular and multicellular forms in filaments or aggregates also occur. Multiplication occurs by either binary fission, budding, constriction, fragmentation, or by unknown mechanisms.