Isolation of biosurfactant producers and characterization of produced biosurfactants from Sungai Dungun Estuary, Terengganu

Surface-active agent or surfactant is a compound that can reduce surface tension of liquid, air interface, and interfacial tension of immiscible liquid phases. The main concern regarding surfactant is the usage of chemical surfactants that have several disadvantages including less biodegradable, more toxic and can lead to dermatological problems. Biosurfactant, a natural surfactant which is mainly produced by bacteria, yeasts, and fungi has become a subject of interest by many researchers as an alternative to substitute the long-established chemical surfactants due to its properties such as more environmentally friendly, biodegradable, biocompatible, and low in toxicity. Therefore, this study was conducted to isolate the potent biosurfactant producers from Sungai Dungun estuary and characterize the produced biosurfactants by qualitative and quantitative assays. Biosurfactant production was screened through several assays based on a) surface activity (oil spreading test, drop collapse test and surface tension measurement), b) emulsification activity (emulsification index (EI24)), and (c) specific tests (hemolytic test and CTAB methylene blue agar tests). Twelve potent biosurfactant producing bacteria were successfully isolated from Sungai Dungun estuary by using Minimal Salt Media (MSM) with an addition of 1 % (v/v) engine oil. Based on the BLAST analyses of 16S rRNA gene sequences, the isolated bacteria was identified to have close relatedness with bacteria species as follows: DSA1 (Bacillus albus, 99%), DSA6 (Acinetobacter venetianus, 98%), DSB7 (Pseudomonas aeruginosa, 99%), DWA5 (Acinetobacter seifertii, 93%), DWA9 (Pseudomonas plecoglossicida, 97%), DWB5 (Chryseobacterium cucumeris, 87%), DWC1 (Aeromonas taiwanensis, 98%), DWC2 (Aeromonas caviae, 98%), DWC4 (Aeromonas caviae, 99%), DWC7 (Delftia lacustris, 99%), DWC8 (Pseudomonas protegens, 99%) and DWC9 (Alcaligenes faecalis, 98%). Four strains which are DSA1, DSB7, DWA5 and DWC1 were highlighted based on significant activities of their biosurfactants in surface tension reduction and emulsification. Biosurfactant of P.aeruginosa DSB7 showed the highest surface activity when it presented the lowest value in surface tension measurement (38.48 ± 0.44 mN/m), and the highest emulsification index towards kerosene with the value of 53.57 %. Meanwhile, B.albus DSA1, A.seifertii DWA5 and A.taiwanensis DWC1 were remarked to produce bio-emulsifiers with better emulsification activity towards used engine oil with index values of 73.81 %, 75.61 % and 85.67 % respectively, which were higher than index value of synthetic surfactant, Sodium Lauryl Sulfate (SLS). The FT-IR spectroscopy analysis revealed that the crude biosurfactants extracted by chloroform-methanol (2:1) solvent extraction from B.albus DSA1 and P.aeruginosa DSB7 to have nature of glycolipid due to the presence of aldehyde group in the Infra-Red (IR) spectra. Meanwhile, crude biosurfactants of A.seifertii DWA5 and A.taiwanensis DWC1 might be a polymeric compound that contains combination of carbohydrates and protein in the structure.