Evaluation of antimicrobial and antioxidant activities of local microalgae isolates chorella sorokiniana (UKM2), Chlorella sp. (UKM8) and Scenedesmus sp. (UKM9)

Abstract

The potential of the local microalgae isolates as source for antimicrobial compounds are yet to be discovered. Therefore, this research aimed to investigate the biomass potential of three local microalgae namely Chlorella sorokiniana (UKM2), Chlorella sp. (UKM8) and Scenedesmus sp. (UKM9) for their antimicrobial and antioxidant properties. The following objectives were proposed to achieve this aim, 1) to assess the growth performance of UKM2, UKM8 and UKM92) to evaluate the antibacterial, cytotoxicity, antiviral and antioxidant activities of biomass extracts or selected fractions, as well as 3) to determine the chemical profile and extrapolate to the biological properties of the most active extracts. The study was initiated by determining the microalgae growth performance in Bold Basal Medium (BBM) followed by biomass extraction with methanol (-ME). Bio-guided assay was implemented to evaluate the antimicrobial and antioxidant properties of the microalgae. The antibacterial activity of UKM2-, UKM8-, UKM9-ME were screened on eighteen bacterial pathogens using the disc diffusion method, followed by cytotoxicity assay using MTT assay towards Vero cells. Microalgae-ME with the highest antibacterial activity was selected for fractionation and further analysis. Fractionation was performed using gradient of solvents systems for antibacterial evaluation by minimum inhibitory concentration (MIC). Fractions with the highest antibacterial activity were investigated for their cytotoxicity, antiviral and antioxidant properties. Antiviral activity was performed against human herpes virus (HHV-1) by plaque reduction assay. Antioxidant properties were determined by (2,2-diphenyl-1-picrylhydrazyl) DPPH radical scavenging activity and total phenolic content (TPC) assays. The chemical profile of the active fractions was determined using gas chromatography-mass spectrometry GC-MS. The growth performance of UKM2, UKM8 and UKM9 showed maximum specific growth rate of 0.3877, 0.4476 and 0.4465 day-1 , respectively. The yield of biomass extracted with methanol were as follows: UKM2 (0.95-0.16 g L -1 ), UKM8 (0.75-0.19 g L -1 ), and UKM9 (0.85-0.25 g L -1 ). UKM8-ME showed the highest antibacterial activity among the isolates. All the isolates did not exhibit cytotoxicity against Vero cells with CC50 values of UKM2 (0.971 mg mL-1 ), UKM8-ME (4.21 mg mL-1 ) and UKM9 ME (1.734 mg mL-1 ). Fractionation of UKM8-ME produces seven fractions (F1-F7) with MICs values ranging from 0.312 to 6.25 mg mL-1 . Fractions F5 and F6 with highest antibacterial activity were further evaluated and found to be non-cytotoxic towards Vero cells with CC50 values, 3.113 and 1.934 mg mL-1 , respectively. The highest selective index (CC50/MIC) was obtained for F6 against S. aureus, S. epidermidis, MRSA and E. coli at 46, 46, 25 and 13, respectively. Antiviral activity potential is noted in the selected extract and fractions from the calculated selective index (CC50/EC50) values: UKM8-ME (19), F6 (15) and F5 (13). Antioxidant evaluation showed higher IC50 for F6 followed by UKM8-ME and F5 with 149.65, 198.78 and 240.09 µg mL-1 , respectively. TPC assay revealed higher phenolic content in UKM8-ME and F6 followed by F5 (254.79, 206.06 and 81.11 mg GAE g−1 , respectively). The chemical profile of UKM8-ME, F5 and F6 accounts for a total of 150 compounds with significantly correspond to antimicrobial and antioxidant activities. The most obvious compound in UKM8-ME includes phenol, hexasadecatrienoic acid, phytol, tridecane and isopropyl miristate, 7,10,13-hexadecatrienoic acid, 9,12-Octadecadienoic (Z,Z) acid and tetratriacontane acid. In conclusion, Chlorella sp. UKM8 showed good antimicrobial and antioxidant potential in association with compounds that are worth for future commercial applications.