The manner in which fungal endophytes activate host stress response systems is unknown; the occurrence of additional mechanisms involved in symbiotically-conferred stress tolerance in mangrove plants (the primary producers of estuarine food chain) is also an unresolved issue. Here, we report antioxidant potentials of four different mangroves and their endophytic fungi. We elucidated the possible roles of antioxidants in symbiotic association between mangroves and their endophytic fungi. Four different mangrove species and the predominant endophytic fungus Aspergillus flavus were analyzed using various in vitro assay systems (such as iron chelating capacity, reducing power, and hydroxyl radicals/hydrogen peroxide/l-diphenyl-2-picrylhydrazyl radical scavenging and inhibition of lipid peroxidation using the β-carotene–linoleate model system). In vitro models clearly established the antioxidant potency of extracts of mangrove plants and their respective endophytic fungi, which aids in understanding the mutualistic associations of plant and endophyte against various biotic and abiotic stresses. Re-infection analysis of endophytic A. flavus in tobacco plants confirmed the endophytic status of the fungus and its enhancement effect on plant growth.

Alkaline cellulases were screened from 54 fungal isolates obtained from mangrove leaves and mangrove wood litters as endophytes and wood litter fungi, respectively. Only three fungal isolates tested positive for alkaline cellulases under plate assay, among which Chaetomium sp. (NIOCC 36) was found to grow in a wide range of pH (between 4 and 12). This alkaline tolerant fungus was further tested for production of alkaline cellulases (β-endoglucanase, β-exoglucanase, β-glucosidase) using agricultural and industrial wastes as substrates in submerged fermentation (SMF) and solid state fermentation (SSF) processes. Cotton seed under SSF conditions had maximum enzyme production at high alkaline pH. Cellulase enzymes produced under alkaline cotton seed SSF conditions at 50°C had higher stability and activity than under non-alkaline conditions (range tested: pH 5, 7, 12). The agricultural and industrial wastes used as carbon sources were economical for commercial production of cellulose. The high specific activity, and stability of cellulases under neutral to alkaline pH and high temperature will be of use in various industrial and biotechnological applications.

No abstract