Fungal-Bacterial Combinations in Plant Health under Stress: Physiological and Biochemical Characteristics of the Filamentous Fungus and the Actinobacterium sp. ISTPL4 under In Vitro Arsenic Stress.

Fungal-bacterial combinations have a significant role in increasing and improving plant health under various stress conditions. Metabolites secreted by fungi and bacteria play an important role in this process. Our study emphasizes the significance of secondary metabolites secreted by the fungus alone and by an actinobacterium sp. ISTPL4 under normal growth conditions and arsenic (As) stress condition. Here, we evaluated the arsenic tolerance ability of alone and in combination with sp. ISTPL4 under in vitro conditions. The growth of and sp. ISTPL4 was measured in varying concentrations of arsenic and the effect of arsenic on spore size and morphology of was determined using confocal microscopy and scanning electron microscopy. The metabolomics study indicated that alone in normal growth conditions and under As stress released pentadecanoic acid, glycerol tricaprylate, L-proline and cyclo(L-prolyl-L-valine). Similarly, d-Ribose, 2-deoxy-bis(thioheptyl)-dithioacetal were secreted by a combination of and sp. ISTPL4. Confocal studies revealed that spore size of decreased by 18% at 1.9 mM and by 15% when in combination with sp. ISTPL4 at a 2.4 mM concentration of As. Arsenic above this concentration resulted in spore degeneration and hyphae fragmentation. Scanning electron microscopy (SEM) results indicated an increased spore size of in the presence of sp. ISTPL4 (18 ± 0.75 µm) compared to alone (14 ± 0.24 µm) under normal growth conditions. Our study concluded that the suggested combination of microbial consortium can be used to increase sustainable agriculture by combating biotic as well as abiotic stress. This is because the metabolites released by the microbial combination display antifungal and antibacterial properties. The metabolites, besides evading stress, also confer other survival strategies. Therefore, the choice of consortia and combination partners is important and can help in developing strategies for coping with As stress.