Iron-Manganese Nodules Harbor Lower Bacterial Diversity and Greater Proportions of Proteobacteria Compared to Bulk Soils in Four Locations Spanning from North to South China

The bacterial abundance and community composition in four types of soils and their associated Fe-Mn nodules from Queyu (QY) in Shandong Province, Zaoyang (ZY), Wuhan (WH) in Hubei Province and Guiyang (GY) in Hunan Province, China were investigated using real-time PCR, cloning and sequencing approaches. It was found that the bacterial 16S rRNA gene copy numbers in the soils were almost 3 magnitudes greater than those in their corresponding nodules and positively correlated with OM. The bacterial diversity as indicated by Simpson and Shannon indices, were significantly lower in the nodules than in the soils. Remarkable divergence in bacterial community structure was observed between the soils and the nodules, and the difference was the mainly explained by OM. In contrast, the differences within the soils and within the nodules were minor, suggesting significant habitat filtering for the bacterial community composition in the nodules. Acidobacteria was the most abundant group (accounting for 28.6%–51.6%) in soil bacterial community while nodule bacterial community was predominated by Proteobacteria (accounting for 62.8%– 90.5%). A number of clones closely related to well-known Mn-oxidizing, Fe-oxidizing and Fe-reducing bacteria within Proteobacteria were retrieved mainly from nodules.