Which of the following organisms is often studied for its role in nutrient cycling?

Bacteria are key players in nutrient cycling due to their diverse metabolic abilities and roles in various biogeochemical processes. They are responsible for decomposing organic matter, which releases nutrients back into the soil, making them available for plants and other organisms. Bacteria also play a vital role in processes such as nitrogen fixation, where atmospheric nitrogen is converted into forms usable by living organisms. Furthermore, certain bacteria are involved in the mineralization of dead organic material, which is crucial for maintaining ecosystem health and soil fertility.

While other organisms like protozoa and helminths can influence nutrient cycling, their roles are generally less central than those of bacteria. Protozoa, for instance, can help control bacterial populations and contribute to organic matter decomposition but do not have the same extensive role as bacteria in nutrient transformation. Helminths are primarily associated with parasitism and their specific contribution to nutrient cycling is often indirect. Viruses can impact microbial communities and nutrient dynamics through lysis of bacteria, but they do not directly participate in the recycling of nutrients in the same way that bacteria do. Thus, bacteria stand out as the primary organisms studied for their direct involvement in nutrient cycling.