Ectomycorrhizal fungus Pisolithus sp. produces extracellular phenolic compounds with antioxidant characteristics in response to in vitro osmotic and matric water stress

Abstract

Ectomycorrhizal fungi are known to synthesize phenolics, carotenoids, pulvinic acids, quinones and terpenoids which help in scavenging reactive oxygen species (ROS) produced due to stress conditions such as temperature, radiation, nutrient depletion, metal toxicity, salinity and competition. Pisolithus sp. PtC1, a basidiomycete fungus, was isolated from ectomycorrhizal association with roots of Acacia mangium tree from a mining site. Fourier Transform Infrared (FTIR) analysis of the extracellular culture broth showed presence of hydroxyl groups indicating antioxidant compounds. When studied for in vitro response towards osmotic stress, the isolate was able to grow till 2.0 percent sodium chloride. In response to matric stress, growth was seen till 15.0 percent polyethylene glycol 6000. In both cases, Pisolithus sp. PtC1 produced intense extracellular golden-brown colouration. The concentration of phenolic compounds released into the extracellular medium was determined in terms of total phenols. In absence of osmotic and matric stress, the concentrations were found to be 1.02 Mu g/mL and 2.34 Mu g/mL, respectively, and increased to 3.23 Mu g/mL in 2.0 percent sodium chloride and 6.96 Mu g/mL in 10.0 percent polyethylene glycol 6000. Antioxidant properties of the culture broth were measured using reducing power assay and total antioxidant activity assay. Statistical correlation analysis revealed very strong positive relationship between concentration of phenols and antioxidant characteristics. Thus, elaboration of phenols may be a water stress tolerance mechanism in Pisolithus sp. through non-enzymatic antioxidant response. These extracellular phenolic compounds can be a potential source of antioxidants.