The correct answer is option 'A' - Anaerobic bacteria.

Explanation:
Bacteria that decompose organic wastes are called anaerobic bacteria. Let's understand why anaerobic bacteria are the correct answer:

1. Decomposition of organic wastes: Organic wastes such as dead plants, animals, and other organic matter contain complex molecules that need to be broken down into simpler forms for recycling in the ecosystem. This process is called decomposition.

2. Oxygen requirement: Aerobic bacteria require oxygen to carry out the process of decomposition. They use oxygen to break down complex molecules into simpler ones. On the other hand, anaerobic bacteria do not require oxygen and can carry out decomposition in the absence of oxygen.

3. Anaerobic conditions: Organic waste often accumulates in environments where oxygen is limited, such as deep layers of soil, sediments at the bottom of lakes or oceans, and the digestive tracts of animals. In such anaerobic conditions, anaerobic bacteria thrive and play a crucial role in decomposing organic matter.

4. Types of anaerobic bacteria: There are various types of anaerobic bacteria that are involved in decomposition. For example, methane-producing bacteria break down organic matter and produce methane gas as a byproduct. Sulfate-reducing bacteria break down organic matter using sulfate instead of oxygen.

5. Importance of decomposition: Decomposition is an essential process in nature as it helps in the recycling of nutrients. When organic matter is decomposed, nutrients like carbon, nitrogen, and phosphorus are released back into the environment, making them available for other organisms to use. This nutrient cycling is important for the functioning of ecosystems.

In conclusion, anaerobic bacteria are the bacteria that decompose organic wastes. They can carry out the process of decomposition in the absence of oxygen and play a vital role in nutrient recycling in ecosystems.