Antibacterial effect of the Trichoderma viride fungi on soil microbiome during PAH's biodegradation

• The presence of T. viride influenced the dynamics of bacterial community.
• The presence of fungi reduced the number of bacterial species within community.
• The maximal PAH degradation reached 78% in the soil inoculated with S3 consortium.
• The PAH biodegradation by T. viride as a sole microorganism did not exceed 47%.
• Trichoderma viride had negative effect on consortial degradation of PAH.

The aim of this study was to evaluate the influence of Trichoderma viride on the metabolic activity and the community dynamics of soil bacteria during polyaromatic hydrocarbons (PAHs) biodegradation. Sixteen PAHs were introduced into soil microcosms mimicking natural conditions to achieve an initial concentration of 2000 mg kg−1 of soil. After 12 months of treatment, the efficiency of PAH removal was of 78% for the microcosms inoculated with a PAH-degrading bacterial consortium designated S3, 64% for those inoculated with the consortium S3 + T. viride, whereas an efficiency of only 47% was achieved in the microcosms inoculated with T. viride alone. Flow cytometry analysis of the bacterial metabolic activities, expressed as the oxidation-reduction potential, allowed differentiating single cells with regard to their metabolic activities. Prior to its introduction in soil microcosms, the consortium S3 consisted of 195 bacterial species which were identified by employing next generation sequencing (MiSeq, Illumina). It has been established that significant changes in the composition of the bacterial community occurred during the biodegradation process when it was carried out in the presence of T. viride. After such treatment only 73 bacterial species were identified from the metabiome, with the dominance of Stenotrophomonas retroflexus (47.46%), Ochrobactrum intermedium (25.83%) and Citrobacter freundii (19.87%). T. viride was able to degrade PAHs; however its presence mainly contributed to modify the bacterial metabiome via antagonistic interactions with the bacteria, which notably reduced the biodegradation efficiency and biodiversity in the microcosms.