Short-term dynamics of culturable bacteria in a soil amended with biotransformed dry olive residue

Dry olive residue (DOR) transformation by wood decomposing basidiomycetes (e.g. Coriolopsis floccosa) is a possible strategy for eliminating the liabilities related to the use of olive oil industry waste as an organic soil amendment. The effects of organic fertilization with DOR on the culturable soil microbiota are largely unknown. Therefore, the objectives of this study were to measure the short-term effects of DOR and C. floccosa-transformed DOR on the culturable bacterial soil community, while at the same time documenting the bacterial diversity of an agronomic soil in the southeastern Iberian Peninsula. The control soil was compared with the same soil treated with DOR and with C. floccosa-transformed DOR for 0, 30 and 60 days. Impact was measured from total viable cells and CFU counts, as well as the isolation and characterization of 900 strains by fatty acid methyl ester profiles and 16S rRNA partial sequencing. The bacterial diversity was distributed between Actinobacteria, Alphaproteobacteria, Gammaproteobacteria, Betaproteobacteria, Bacilli, Sphingobacteria and Cytophagia. Analysis of the treatments and controls demonstrated that soil amendment with untransformed DOR produced important changes in bacterial density and diversity. However, when C. floccosa-transformed DOR was applied, bacterial proliferation was observed but bacterial diversity was less affected, and the distribution of microorganisms was more similar to the unamended soil.