Rucete ✏ Campbell Biology In a Nutshell
Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 27.6 Prokaryotes Have Both Beneficial and Harmful Impacts on Humans
While prokaryotes are often associated with disease, the vast majority play beneficial roles in human health, agriculture, biotechnology, and environmental management. Understanding both sides of prokaryotic interactions is essential to human well-being and scientific advancement.
Mutualistic Bacteria in the Human Body
- The human gut microbiome contains 500–1,000 species of bacteria, outnumbering human cells 10 to 1.
- These bacteria help:
- Digest foods we can’t break down ourselves.
- Synthesize essential nutrients (e.g., vitamins).
- Regulate intestinal development and immune responses.
- Example: Bacteroides thetaiotaomicron has genes for digesting carbohydrates and signaling human cells to build capillaries and produce antimicrobial compounds.
Pathogenic Bacteria and Disease
- All known pathogenic prokaryotes are bacteria.
- They cause about half of all human diseases, including:
- Tuberculosis (Mycobacterium tuberculosis)
- Cholera (Vibrio cholerae)
- Lyme disease (Borrelia burgdorferi, transmitted by ticks)
- Illness is typically caused by toxins:
- Exotoxins: Proteins secreted by bacteria (e.g., cholera, botulism).
- Endotoxins: Released only when gram-negative bacteria die and their cell walls break down (e.g., Salmonella).
- Horizontal gene transfer can turn harmless bacteria into dangerous pathogens (e.g., E. coli O157:H7 contains over 1,000 genes absent in normal E. coli).
Antibiotic Resistance Crisis
- Overuse of antibiotics in medicine and agriculture has selected for resistant strains.
- Resistance evolves rapidly due to:
- Fast reproduction
- Mutation accumulation
- Horizontal gene transfer spreading resistance genes
- Examples:
- XDR-TB (extensively drug-resistant tuberculosis) killed 52 out of 53 patients in a 2006 South African outbreak.
- MRSA (methicillin-resistant Staphylococcus aureus) has become widespread and difficult to treat.
- New hope: Malacidins (soil-derived antibiotics) and teixobactin show promise against multidrug-resistant bacteria.
Prokaryotes in Biotechnology and Industry
- Long used in food production: yogurt, cheese, beer, wine, soy sauce.
- Engineered bacteria are used to:
- Produce vitamins, hormones, antibiotics
- Clean up pollution (bioremediation)
- Synthesize biodegradable plastics (e.g., PHA)
- Convert biomass to ethanol
- CRISPR-Cas system, derived from bacterial immunity, now revolutionizes genetic engineering in research and medicine (e.g., targeting HIV-infected cells).
In a Nutshell
Prokaryotes impact humans both positively and negatively. While some cause disease and evolve resistance to antibiotics, many more are essential for digestion, agriculture, and biotechnology. Their metabolic versatility and rapid evolution make them both powerful allies and formidable challenges in health and science.