Biomedical Engineering Reference
In-Depth Information
Chapter 4
Overview of Class Bacteria
“The beginnings and endings of all human undertakings are untidy.”
John Galsworthy
Bacteria
Proteobacteria
Alpha Proteobacteria (Chapter 5)
Beta Proteobacteria (Chapter 6)
Gamma Proteobacteria (Chapter 7)
Epsilon Proteobacteria (Chapter 8)
Spirochaetes (Chapter 9)
Bacteroidetes (Chapter 10)
Fusobacteria (Chapter 10)
Firmicutes
Bacilli (Chapter 12)
Clostridia (Chapter 12)
Mollicutes (Chapter 11)
Chlamydiae (Chapter 13)
Actinobacteria (Chapter 14)
To understand the classification of bacteria, let us look at the controversy at
the root of the tree of life. Three major groups of organisms account for all
life on earth: eubacteria, archaea, and eukaryotes. When you compare species
of Class Eubacteria with species of Class Archaea, you're not likely to notice
any big differences. The eubacteria have the same shapes and sizes as the
archaea. All species of eubacteria and all species of archaea are single-celled
organisms, and they all have a typical prokaryotic structure (i.e., lacking
a membrane-bound nucleus to compartmentalize their genetic material). As
it happens, Class Eubacteria contains all of the bacterial organisms that are
known to be pathogenic in humans. The Archaeans are non-pathogenic; most
are extremophiles, capable of living in hostile environments (e.g., hot
springs, salt lakes), but some Archaean species can occupy less-demanding
biological niches (e.g., marshland, soil, human colon). Class Archaea does
