Responses of soil bacterial community after seventh yearly applications of composted tannery sludge

Composted tannery sludge (CTS) contains organic compounds and inorganic elements, mainly chromium (Cr), and its long-term application in soil can alter the bacterial structure and diversity. Thus, we used the next-generation sequencing to assess the structure and diversity of bacterial communities in soils after 7 years of CTS application. CTS was applied at 0, 2.5, 5, 10, and 20 Mg ha− 1 and the soil samples were collected at 75 days after application in the seventh year. The most abundant phyla were Actinobacteria, Proteobacteria, Firmicutes, and Chloroflexi. The abundance of some specific groups increased with application of CTS, such as Anaerolinea S0208 and Firmicutes. Six bacterial genera differed between amended and unamended soil. The abundance of Bacillus, Paenibacillus, Symbiobacterium, Clostridium, Microlunatus, and Actinomadura increased after application of CTS. The Redundancy Analysis between the structure of the bacterial community and chemical variables in soil did not cluster all treatments clearly, but showed Cr, pH, and organic C as significant chemical variables that influenced the bacterial communities. Application of CTS in soil has a primary effect on the bacterial communities that, negatively, alter the bacterial diversity and community similarity, while that, positively, it permits to select specific bacterial groups able to resist and biodegrade contaminants