Effects of bacterial nitrogen transfer on fungal growth in nitrogen-deprived environments

Biotransformation of organic contaminants is often impeded by a lack of nutrients relevant for growth and metabolic (co-metabolic) activity of fungal and bacterial degraders. While a growing number of studies have addressed the promoting role of fungal mycelia in bacterial activity and contaminant turnover, less is known on bacterial effects potentially supporting fungi in their functional interaction in the soil mycosphere (the zone surrounding and affected by hyphae). For instance, fungi are unable to fix atmospheric nitrogen and, hence, partly rely on the partnership with nitrogen-fixing bacteria. Here, we hypothesise that nitrogen-fixing bacteria in the mycosphere provide nitrogen to fungi to support growth and potential contaminant degradation in nitrogen-deprived environments. To challenge our assumption, we tested the impact of N-fixing soil bacteria (i.e. polycyclic aromatic hydrocarbon (PAH) degrading Pseudomonas sp SK1, Sphingomonas sp. LH162, and non-PAH degrading Azotobacter vinelandii B671) on growth of contaminant degrading basidiomycetes Coprionopsis cinerea and Pleurotus ostreatus using N-free agarose plates and liquid media at ambient air conditions. Relative to bacteria-free controls, bacterial-fungal co-cultures showed significantly increased fungal growth suggesting a fungal uptake and utilization of fixed nitrogen. Using stable isotope probing approaches, current work quantifies dynamic biomass development and concomitant N and C-flows between Azotobacter vinelandii B671 and Coprinopsis cinerea, and its impact on biodegradation of soil contaminants such as PAH.