Prokaryotes

Microbiology, the study of microscopic organisms (microbes), has a historical context rooted in the skepticism and fear associated with these organisms.
Antonie van Leeuwenhoek, recognized as the "father of microbiology," was the first to observe microbes through a microscope.

The human body contains approximately 39 trillion microbes.
- Microscopic organisms include bacteria, archaea, and other similar entities.
In comparison, the average human body is composed of roughly 30 trillion human cells.
Human microbiome: Refers to the entire collection of microbes inhabiting and on human bodies.
- Influences multiple aspects of human health and characteristics.
- Gut health: Affects digestive processes and illness susceptibility.
- Brain function: Microbial health can influence mental health and neurological function.
- Body odor: Microbial composition contributes to an individual's scent.
- Risk of infection: Microbes can modulate the immune response.
- Attractiveness to others and mosquitoes: Microbial activity can influence natural pheromones and body odors that affect attractiveness.

There are three domains of life: Bacteria, Archaea, and Eukarya.
- Bacteria were the first to diverge from a common ancestor shared with Archaea and Eukarya.
Evidence from rocks called stromatolites indicates that bacteria existed approximately 3.7 billion years ago.
- Stromatolites exhibit patterns that signify bacterial activity.

Prokaryotes: Single-celled organisms that include both Bacteria and Archaea.
- Defining features include:
- A single loop of DNA
- Smaller size compared to eukaryotic cells
- Lack of membrane-enclosed organelles
- Rapid reproduction, capable of doubling in number in 10 to 30 minutes.
Prokaryotes dominate life on Earth, with Bacteria and Archaea constituting over two-thirds of all species.

Basic structural components:
- Cell wall: Protects the cell and surrounds the plasma membrane.
- Capsule: Present in some bacteria; aids in evading the immune system.
- Pili: Short, hair-like structures that help link bacteria together and adhere to surfaces.
- Flagella: Long, whiplike tails used to propel bacteria through liquid environments.

Microbes, including bacteria and archaea, communicate using quorum sensing:
- This is a form of cell-to-cell communication that allows bacteria to detect population densities and respond collectively.
Biofilm formation process explained:
1. Free-swimming bacteria attach to surfaces.
2. Slimy secretions protect and anchor the bacteria.
3. Signaling molecules enable bacteria to sense their numbers (quorum sensing).
4. Some bacteria might disperse from mature biofilms to find new areas to colonize.

Prokaryotes can be divided into two major metabolic types:
- Aerobes: Require oxygen for survival.
- Anaerobes: Can survive without oxygen; some are classified further as:
- Methanogens: Produce methane gas by feeding on hydrogen.
- Certain anaerobes perform fermentation.
Some prokaryotes can switch between aerobic and anaerobic metabolism.

The first photoautotrophs were prokaryotes, specifically cyanobacteria, an aquatic bacteria type.
Hypotheses regarding oxygen generation by cyanobacteria:
- Possible facilitation of the evolution of eukaryotic organisms, particularly multicellular forms.
- Membrane-bound organelles, like chloroplasts, may have played a role in oxygen accumulation in the atmosphere.

Nitrogen fixation: The conversion process where specific bacteria utilize nitrogen gas from the air and transform it into ammonia.
Importance: Plants require nitrogen in the form of ammonia or nitrate but cannot synthesize it independently.
- Earth’s atmosphere is approximately 78% nitrogen.

Without microbes, the consequences for humans and the environment would be dire:
- Absence of oxygen for breathing.
- Lack of plants for food sources.
- Inability to process critical micronutrients.
- Accumulation of dead skin cells.