1. Probiotics: These beneficial bacteria live in our gut and help with digestion, nutrient absorption, and immune function. They can be found in fermented foods like yogurt and kimchi, or taken as supplements.

2. Nitrogen-fixing bacteria: These bacteria play a crucial role in the nitrogen cycle, converting atmospheric nitrogen into usable forms that plants can absorb. This is essential for plant growth and overall ecosystem health.

3. Decomposers: These bacteria break down dead organic matter, such as leaves, wood, and animal waste. This process releases nutrients back into the soil, which is essential for plant growth and nutrient cycling.

4. Lactic acid bacteria: These bacteria are used in food production, such as yogurt, cheese, and sauerkraut. They create lactic acid, which gives these foods their characteristic sour flavor and also acts as a natural preservative.