Effect of carbon and nitrogen input on the bacterial community structure of Neocaledonian nickel mine spoils

Neocaledonian mine spoils are considered as an extreme environment because of their edaphic conditions, which are unfavourable for life. The principal characteristics of this soil are the high nickel content (20,000 ppm) and the very low carbon (0.2%) and nitrogen (0.01%) levels, which are certainly among the major limiting factors for heterotrophic bacterial growth. The aim of this work was to determine what changes could occur in the bacterial community structure of the mine spoils when a carbon and a nitrogen source were added. Soil bacterial response to nutrient addition was examined in both the mine spoils and an agricultural soil, which is characterized by normal levels of nutrients. 16S rRNA gene clone libraries constructed to characterize changes occurring in the different soil bacterial communities showed an important selection of Actinobacteria in the mine spoils as a consequence of nutrient amendment: Actinobacteria represented 75% and 96% of the bacterial community structure after succinate and glucose addition, respectively. This was observed only in the mine spoils and is probably a consequence of the extreme environmental conditions. Carbon amendment in the agricultural soil led to an increase in Firmicutes, mainly Bacillus sp.