In vitro antioxidant activity of haloalkaliphilic fungal extracts from lake Magadi

Abstract

The wide-ranging saline-alkaline ecological setting is steadily acquiring appreciation as a rich source harbouring a repertoire of extremophilic fungal diversity exerting exclusive biological activities ranging from anti-inflammatory, antipyretic, analgesic among other varied medicinal capacities. However, studies characterizing biochemical functionalities from structurally unique haloalkaliphilic fungal biota remain scanty and undocumented. Importantly, saline emitting hot-springs situated in Rift valley soda lakes are gaining recognition as natural reservoirs with enormous fungal microbial community bearing potential for antioxidation capacity. Therefore, we conducted a cross-sectional laboratory based experimental study through random sampling aimed at characterizing in vitro antioxidant activity from haloalkaliphilic fungal strains of Lake Magadi in Kenya. Sample types comprising wet sediments, soils and surface water were cultured in sabouraud’s dextrose agar (SDA), potato dextrose agar (PDA) and malt extract agar (MEA) plates at temperatures of 250 c and 410 c respectively, for 1-3 weeks. Resulting pure isolates underwent molecular identification. PCR proceeded using ITS-1 & 4 universal primers followed by Sanger sequencing. NCBI’s nBLAST supported molecular identification with ≥90% identity cut-off values. Fermentation and extracts production progressed for 28 days at 250 c accompanied by lyophilisation. Yielded freeze-dried extracts were profiled for antioxidant activity through hydroxyl, superoxide, DPPH, hydrogen peroxide, FRAP and lipid peroxidation inhibition assays. Extracts’ total phenolics and flavonoids content were also estimated. IC50 was tabulated based on dose-response curves against standards through linear regression. One-way ANOVA compared means across treatments and Tukey’s post hoc used for pairwise group comparisons. Statistical significance was considered at P≤0.05. Genera Cladosporium exhibited dominance (n=4) among sampled fungal biota. Samples P1, P6, P9 and P5 extracts exhibited maximal scavenging activity at higher concentrations against hydroxyl (76.53% ± 1.27), superoxide (78.90% ± 1.29), H202 (76.19% ± 0.40) and DPPH (80.19% ± 0.94) radicals, respectively. Ferric reductive (0.583 ± 0.005) and lipid peroxidation inhibitive (80.95% ± 1.07) activities for isolate P5 was statistically higher relative to other profiled extracts. Radical scavenging capacity of respective antioxidant standards was substantially higher against assayed extracts. Profound IC50 scavenging effect occurred at extract concentrations between 2.5 - 3.5 mg/ml. P7 extracts revealed peak total phenolic content of 3.61 ± 0.05 mg gallic acid equivalents/mg crude extract at 4mg/ml, while P6 expressed comparable total flavonoid content of 3.32 ± 0.04 mg quercetin equivalents/mg crude extract. Overall, fungi extracts showcased free radicals scavenging ability against reactive species in assorted antioxidant assays. Besides safety profile validation, our extracts demonstrate applicability for antioxidative potential that may further be discerned via comparative in vivo and ex vivo murine experimentation models.