Survey of Bacteria: Low G + C Gram-Positive Bacteria

Low G + C Gram-Positive Bacteria

• Clostridia are rod-shaped, obligate anaerobes that form endospores and are important in medicine and industry.
• Clostridia are related to Epulopiscium, sulfate-reducing microbes, and Selenomonas.
• Mycoplasmas are facultative or obligate anaerobes that lack cell walls and are the smallest free-living cells.
• Mycoplasmas colonize mucous membranes of the respiratory and urinary tracts.
• Other low G + C Gram-positive bacilli and cocci include Bacillus, which forms endospores and is commonly found in soil.
• Bacillus thuringiensis toxin is used as an insecticide by farmers and gardeners, while Bacillus anthracis causes anthrax.

General Characteristics of Prokaryotic Organisms

• Epulopiscium and its relatives have a unique method of reproduction, known as viviparity, where live offspring emerge from the body of the dead mother cell.
• Prokaryotic cells can have different arrangements, such as chains or clusters, depending on the planes in which they divide and the separation of daughter cells.

Modern Prokaryotic Classification

• Modern prokaryotic classification is based on genetic relatedness of rRNA sequences.
• There are three domains: Archaea, Bacteria, and Eukarya.

Gram-Negative Proteobacteria

• Class Alphaproteobacteria includes pathogenic alphaproteobacteria, such as Rickettsia, which is transmitted through the bite of an arthropod and causes several human diseases, and Brucella, which causes brucellosis.
• Other alphaproteobacteria include Acetobacter, Gluconobacter, and Caulobacter.
• Class Betaproteobacteria includes pathogenic betaproteobacteria, such as Neisseria, which inhabits mucous membranes of mammals and causes numerous diseases, and Bordetella, which causes pertussis.
• Other betaproteobacteria include Thiobacillus, which recycles sulfur in the environment, and Zoogloea, which forms flocs that assist in the treatment of sewage.
• Class Gammaproteobacteria is the largest and most diverse class of proteobacteria, divided into subgroups such as purple sulfur bacteria, intracellular pathogens, methane oxidizers, glycolytic facultative anaerobes, and Pseudomonads.
• Intracellular pathogens include Legionella, which causes Legionnaires' disease, and Coxiella, which causes Q fever.
• Methane oxidizers use methane as a carbon and energy source and inhabit anaerobic environments.
• Glycolytic facultative anaerobes catabolize carbohydrates by glycolysis and the pentose phosphate pathway.
• Pseudomonads break down numerous organic compounds and are important pathogens of humans and animals.
• Class Deltaproteobacteria includes a wide variety of metabolic types, such as Desulfovibrio, Bdellovibrio, and Myxobacteria.
• Class Epsilonproteobacteria includes important genera such as Campylobacter and Helicobacter.