ch 11 ppt

Prokaryotes Overview

• Focus on Domains: Bacteria and Archaea

Microbial Diversity

• PCR indicates up to 10,000 bacteria per gram of soil.
• Many bacteria remain unidentified due to:
  • Not being cultured.
  • Requiring special nutrients.
  • Existing as part of complex food chains relying on products from other bacteria.
  • Need for culturing to understand metabolism and ecological roles.

Domain Bacteria

• Consists of 24 phyla including:
  • Proteobacteria (major group of Gram-negative bacteria)
  • Nonproteobacteria (includes other Gram-negative bacteria)
  • Gram-positive bacteria
  • Chlamydiae
  • Spirochaetes
  • Bacteroidetes

Phylum: Proteobacteria

• Dominates Gram-negative, chemoheterotrophic bacteria.
• Derived from a common photosynthetic ancestor.
• Named after the Greek god Proteus.
• Classes under Proteobacteria:
  • Alpha
  • Beta
  • Gamma
  • Delta
  • Epsilon

Alpha Proteobacteria

• Thrive in low nutrient environments; may have structures called prosthecae.
• Includes agriculturally significant organisms:
  • Rhizobium: nitrogen-fixing bacteria (converts atmospheric nitrogen to ammonia).
  • Agrobacterium tumefaciens: a plant pathogen causing crown gall via DNA plasmid insertion.
  • Nitrobacter: oxidizes NO2^- to NO3^-.
  • Rickettsia:
  • Obligate intracellular parasites.
  • R. rickettsii causes Rocky Mountain Spotted Fever (transmitted by dog ticks).
  • R. typhi causes endemic typhus (from rodents via fleas).
  • R. prowazekii causes epidemic typhus (human-to-human via lice). High mortality rate.

Applications of Alpha Proteobacteria

• Wolbachia: influences insect behavior and can be targeted with antibiotics to treat roundworm infections.

Beta Proteobacteria

• Utilize nutrients emanating from anaerobic decomposition.
• Notable examples:
  • Thiobacillus: sulfur-oxidizing bacteria.
  • Nitrosomonas: oxidizes NH4^+ to NO2^- (historically confused with Nitrobacter).

Gonorrhea

• Caused by Neisseria gonorrhoeae (Gram-negative diplococci).
• Transmission via sexual contact (organism adheres to mucosal cells, leading to inflammation).
• Symptoms:
  • Males: urethral discharge.
  • Females: potential vaginal discharge, abdominal pain (Pelvic Inflammatory Disease).
• Treatment: antibiotics; prevention through condom use.

Gamma Proteobacteria

• Orders include:
  • Vibrionales: e.g., Vibrio cholerae (causes cholera).
  • Pseudomonadales: e.g., Pseudomonas aeruginosa (opportunistic pathogen).
  • Enterobacteriales (enteric bacteria): e.g., Escherichia coli, Salmonella (causes food infections).
• Yersinia pestis (Plague):
  • Transmitted by fleas from rats to humans; has a high mortality rate.
  • Known for causing historical pandemics. Transmitted primarily via flea bites; can also spread pneumonically.

Delta Proteobacteria

• Includes predatory taxa, e.g., Bdellovibrio that preys on other Gram-negative bacteria.

Epsilon Proteobacteria

• Features helical or vibrioid shapes.
• Includes:
  • Campylobacter jejuni (causes gastroenteritis).
  • Helicobacter pylori (associated with peptic ulcers and gastric cancer).

Gram-positive Bacteria

• Divided into:
  • Low G + C ratio (Firmicutes): includes organisms like Clostridium (e.g., C. botulinum, C. tetani).
  • High G + C ratio (Actinobacteria): includes Mycobacterium (causes tuberculosis, leprosy).
• Important for antibiotic production; e.g., Streptomyces.

Chlamydiae

• Known for unique intracellular life cycle. e.g., Chlamydia trachomatis causes blindness and sexually transmitted disease.
• Lifecycle involves forms that infect host cells (elementary bodies and reticulate bodies).

Spirochaetes

• Pathogenic members include:
  • Treponema pallidum: causes syphilis.
  • Borrelia burgdorferi: causes Lyme disease (transmitted via ticks).
• Symptoms of Lyme disease include localized rash, flu-like symptoms, joint issues.

Bacteroidetes

• Predominantly anaerobic, often found in human intestines.
• Considered to be one of the most prevalent groups of microbes in humans.

Summary

• Understand the diversity and critical roles of prokaryotic domains, emphasizing examples of significant bacteria and their impacts on health, agriculture, and ecosystems.