Functional heterogeneity of metabolites excreted by fungal and bacterial biofilms and their effects on seedling growth

Abstract

Environmental conditions and physical interactions between microbial cells may alter the metabolites released by them. The present study examined the functional differences of metabolites excreted by three biofilms viz., a fungal biofilm of Aspergillus sp. (FB), a bacterial biofilm of Enterobactor sp. (BB), and their mixed-culture biofilm (FBB). All three biofilms were formed under in vitro conditions and their cell-free exudates were analyzed for functional properties using Fourier Transform Infrared (FTIR) spectroscopy. Further, a germination assay was carried out using lettuce seeds. Functional molecules produced by the FBB have clustered separately from the rest showing the distinctiveness of molecules produced by FBB. All three biofilms showed a higher accumulation of functional molecules during their mature stages than that in the early stages of their development. The lettuce seeds treated with FBB exudates showed a noteworthy growth increment in comparison to FB and BB treated seedlings. The highest seedling vigor was shown by lettuce seeds treated with 0.5 day old FBB exudates, while the least was demonstrated in seeds treated with 6 day old BB, FB and FBB exudates. The results suggest that the accumulation of functional molecules seems to incur phytotoxic effects on lettuce seedlings. In conclusion, 0.5 day old FBB exudates can be used to promote the growth of lettuce seedlings. The study emphasizes the importance of selecting specific biofilms over microbes at species level in developing biofertilizers.