Monera is one of five kingdoms of life, the others of which are Protista, Fungi, Plantae, and Anamalia. The Monera kingdom includes both cyanobacteria, or blue-green algae, and true bacteria, also called eubacteria. The discovery of archaebacteria, which are distinctly different in many ways from other bacterial species, resulted in the split of the originally unified Monera kingdom into two sub-kingdoms: Archaebacteriobionta and Eubacteriobionta.
Nuclear Characteristics
Members of the Monera kingdom are more easily referred to simply as bacteria, all of which are single-cell prokaryotic organisms. Prokaryotes, according to "Biochemistry" authors Reginald Garrett, Ph.D., and Charles Grisham, Ph.D., are non-nucleated cells. The prefix "pro," in this case, means "before," while the Greek root "karyot" means "nucleus." The lack of a nucleus distinguishes bacteria from eukaryotes, a word meaning "true nucleus."
Membrane Characteristics
Unlike eukaryotic cells, which form the uni- and multicellular organisms of the other four kingdoms, prokaryotes have only a single membrane. Drs. Garrett and Grisham point out that they can, however, form an internal mesosome, or membranous structure, but the membrane surrounding this area is continuous with the cellular membrane. The function of a mesosome is largely unknown, and it's hypothesized that these structures form only under artificial conditions, including chemical fixation of bacteria for microscopic study.
Organelle Characteristics
While eukaryotes possess a wide variety of membrane-bound organelles, or sub-cellular functional structures, prokaryotes have only non-membranous organelles. Principal among these are the ribosomes, which are cellular machinery responsible for protein production. Some bacteria also have propulsive filaments called flagella.
Shape Characteristics
Bacteria fall into several shape categories, note Drs. Thomas Pollard and William Earnshaw in their text "Cell Biology." Cocci are round, and many coccus-shaped bacteria group together into clusters. The human pathogen Streptococcus, responsible for strep throat, is among these. Bacilli are rod-shaped bacteria, and are the most common of the bacterial shapes. Bacillus anthracis, the human pathogen responsible for anthrax, falls into this shape category. Finally, spiral bacteria, called spirilla, include Chlamydia trachomatis---the bacterial species responsible for the sexually transmitted infection Chlamydia.
Special Characteristics of Archaebacteria
The oldest class of living organisms, Archaebacteria, are Monera that can live in some of the most extreme climates on Earth. Among these special bacteria are the thermophiles, which thrive in hot springs and deep-sea thermal vents, the halophiles, which are capable of surviving in extremely salty ponds and lakes, and methanogens, which produce methane from carbon dioxide and hydrogen gas.
References
- "Biochemistry"; Reginald Garrett, Ph.D., and Charles Grisham, Ph.D.; 2007
- "Cell Biology"; Thomas Pollard, M.D., and William Earnshaw, Ph.D.; 2007
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