Bacteria
Overview
Bacteria are prokaryotic organisms without a nuclear membrane, among the oldest and most diverse life forms on Earth. As single-celled microorganisms, they typically measure 0.5–5 μm in size and exhibit various shapes such as rod-shaped (bacilli), spherical (cocci), and spiral (spirilla). Bacteria exist in nearly all environments, including soil, water, air, and inside the human body, profoundly influencing ecosystem nutrient cycling and human health.
Main Content
Structure and Classification of Bacteria
Bacteria are composed of a cell wall, cell membrane, cytoplasm, ribosomes, and genetic material (DNA). Based on Gram staining, they are classified into Gram-positive bacteria (thick peptidoglycan layer) and Gram-negative bacteria (thin peptidoglycan layer and outer membrane). Representative Gram-positive bacteria include Staphylococcus and Streptococcus, while Gram-negative bacteria include E. coli and Salmonella. Additionally, based on oxygen requirements, bacteria are divided into aerobes, anaerobes, and facultative anaerobes.
Ecological Role of Bacteria
Bacteria act as decomposers in ecosystems, breaking down organic matter into inorganic compounds and supplying nitrogen compounds usable by plants through nitrogen fixation. For example, rhizobia (Rhizobium) live symbiotically in the roots of leguminous plants, fixing nitrogen. Furthermore, the human gut microbiota aids digestion, synthesizes vitamin K and B vitamins, and regulates the immune system.
Bacteria and Disease
Some bacteria act as pathogens, causing infectious diseases. Mycobacterium tuberculosis causes tuberculosis, Vibrio cholerae causes cholera, and Helicobacter pylori causes gastric ulcers and stomach cancer. Bacterial infections are treated with antibiotics, but the emergence of antibiotic-resistant bacteria (e.g., methicillin-resistant Staphylococcus aureus, MRSA) has become a serious public health concern.
Usefulness of Bacteria
Bacteria are utilized in various fields such as industry, medicine, and agriculture. Lactic acid bacteria (Lactobacillus) are used in the production of fermented foods like yogurt and cheese, while E. coli is employed in recombinant DNA technology to produce pharmaceuticals such as insulin and growth hormones. Additionally, Bacillus thuringiensis is used as a biological pesticide, and Pseudomonas species are used for environmental pollutant degradation (bioremediation).
History of Bacterial Research
In the 17th century, Antonie van Leeuwenhoek first observed bacteria under a microscope. In the 19th century, Louis Pasteur demonstrated that fermentation and putrefaction are caused by bacteria, and Robert Koch discovered the causative agents of anthrax, tuberculosis, and cholera, establishing 'Koch's postulates.' In the 20th century, Alexander Fleming discovered penicillin, ushering in the antibiotic era.
Recent Trends
As of 2024–2025, bacterial research focuses on overcoming antibiotic resistance and utilizing the microbiome (human microbial community). Phage therapy using bacteriophages is gaining attention as an alternative for treating antibiotic-resistant bacteria, and CRISPR-Cas9 gene editing technology is being used to manipulate bacterial genomes for research into new biocatalysts or biofuel production. Additionally, the connection between gut microbiota and the gut-brain axis has been revealed, leading to active research on the relationship between mental health and bacteria. In 2024, the WHO updated the 'Global Action Plan on Antimicrobial Resistance,' emphasizing international cooperation for the development of new antibiotics and alternative therapies.
Related Topics
- [[Virus]]
- [[Antibiotic]]
- [[Microbiome]]
- [[Immune system]]
- [[Bioremediation]]
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