Later, in manganese nodules, other species of microorganisms were found which were capable of accumulating iron and manganese. Although the function of microorganisms in manganese and the mechanism of oxidation are still under debate, it is believed that the biogenic factor determines to a considerable extent the manganese destiny on its ways to the ocean. The fine terrigenous material and the greater part of hydrothermal material that enter into the ocean pass through the biogenic filter before they reach the bottom. Manganese species in water and suspension are associated with the occurrence of organic mater and activity of sea bacteria. At the oceanic bottom, manganese and other metals are also affected by the biogenic factor, beginning with the downward flux of organic matter and terminating with benthic activity.
Bacterial activity can affect the growth, structure and composition of nodules.