The correct answer to the question is option 1: bacteria. Bacteria play a crucial role in the decomposition and recycling of organic matter from dead organisms. When organisms die, bacteria break down the organic matter into simpler compounds through a process called decomposition. These bacteria feed on the dead organic matter and release enzymes that help in breaking down complex molecules, such as proteins and carbohydrates, into smaller components.

The decomposition carried out by bacteria is essential for the recycling of nutrients back into the ecosystem. As bacteria break down the organic matter, they release nutrients, such as nitrogen, phosphorus, and carbon, which can then be used by other living organisms for their growth and development. This recycling of nutrients is important for the sustainability of ecosystems.

While options 2 (protozoa) and 3 (virus) are also microscopic organisms, they do not play a significant role in decomposition and recycling of organic matter. Protozoa are primarily involved in consuming bacteria and other small organisms, while viruses are not considered living entities and do not have the ability to decompose organic matter.

Therefore, the correct answer is option 1: bacteria.