Bioprocessing of Biosurfactants from Microbial Sources and their Applications

Abstract

BioSllrfactants are extrncellul llr microbial products that show a high degree of structu ral. functional and chemical heterogeneity. In compnrison with synthe tic !>urfaclants, biosurfactants exhibit environmental compatibility, biod egradnbiJit y~ high reaction rate, astonishing chemical diversity, und better physiochemical characters. In the first phase of study, physicochemical characterization of crude oil affected and unaffected so il of Chak Naurang, Punjab, Pa kistan was done. Results demonstrated that the contaminated soi l was slightly alkaline clay- loam with TPH of 22.2 g/kg and TOe of 23. 11 g/kg. The concentration of nitrogen, phosphorus and potassium was found to be quite low i.e. 0.644 g/kg, 12.46 mglkg and, 20 mwkg, respectively. Enrichment and isolat ion experiments were typi cally dcsi!,1f1ed t.o obtain indigenous biosurfactants producing nucroorganisms of crude oil contaminated soil. Amongst forty isolates, qualitative !U1d quantitative screening for biosurfactants production cOllfinned fourteen potential microorgani sms, which were identified through morphologi cal) microscopic, biochemical and molecular studies. The two 1110st efficient bjosurfactants producing microorganisms i.e. Pseudomonas oerugillDsa MF069166 with 84 % of E.124, 26.6 mN/m of S.T, 8 em of oil displacement zone and, Meyerozyma s1'p. MF1381 26 with 82 % ofE.b .J, 26 mN/m ofS.T and 1.4 em of oil displacement zone were selected for further stlldies of bioprocess optimjzation, characterization and environmen tal applications of biosurfnctants. tn the second phase of study out of five different fennenlation media, M 2 was found 10 be the most suitable for P. aerllgi1l0Sa MF069 I 66 whereas, M 5 for Meyerozyma spp. MF138126. Plackett·Bunnan optimization showed that glycerol, KaHPO.1, peptone, KNOJ, NaCI, yeast ex tract and MgS04 were significant components ofM 2 for maximum rhamnolipids production (3.46 giL) from P. ael'lIglnosa MF069166 whereas, peptone, glycerol, NaH2P04, yeast extract and MgS04 were significant components of M 5 for maximum sophorolipids production (4.02 giL) from Meyerozyma spp. MF138 126. Opti mi zation of cultme conditions using Response Surface Methodology revealed thut the predicted values of pH; 6.5, T; 35 °C, SOl; 3.4 % and agi tation speed of 120 RPM resulted in maximum growth of 3.06 and rhamnoli pids production of 4.3 1 giL fi'om P. (lerl/ginosa MF069 1 66. Lo case of Meyerozyma spp. MF138126, the predicted values of pH; 5.5, T; 33 .2 °C, SOl; 3.3 % and agitation speed of 161 RPM resulted in maximum growth of 3. 17 and sopborolipids production of 6.9 giL. Chemical characterization techniques of TLC, FTIR, RP-HPLC, I Hand 13CNMR and LC-ES I-MS con finned that biosllrfactants produced by P. aemgi/losa MF069166 and Meyerozyma spp. MF138126 were rhamnolipids and sophorolipids, respectively. The stability of rhamnolipids was witnessed from 15-121 IlC T, 4-1 J pH and 2- 10 % NaCI whereas, the stability of sophorolipids W~IS observed from 5-1 15 °C T, 3- 10 pH and 2- 10 % NaCI. Cell surface hydrophobicity (CSH) studies showed more than 50 % affinity of the two isolates for crude oil, hexadecane and dodecane whereas, more than 70 % emulsification activi ty was observed by their respective rhamnolipids and sophorol ipids in the presence of different hydrocarbons. cmc of rhamnolipids was found to be 40 mglL whereas, the cmc of sophorolipids was 50 mglL. z-average diameter of purified rhamnolipids and sophorolipids was noted under the effect of varying elfie, pH and electro lytes through Dynamic Light Scattering technique. In the final phase of study. role of P. aerllgillosa MF069166 and Aleyel'ozyma spp. MF1 38 126 and, their respective rhamnolipids and sophorolipids was evaluated in biodegradation of cnlde oil and bioremediation of heavy metals. In crude oil degradation c:xperimcnts, gntvimetric Hnd GC-MS analysis demonstrated that the bacterial strain degraded 90 % of the petroleum hydrocarbons while the yeast species showed 85 % biodegradation efficiency after 14 days of incubation period. Results of heavy metals bioremediation studies indicated more than 75 % removal of zinc from aqueous phase ancl contaminated soil through metal chelating activity of rhamnolipids. Simil arly, sophorolipids were able to precipitate out more than 80 % of lead from the two phases. Kinetic study of biosurfactants mediated soil washing demonstrated a gradual increase in percentage removal oflead and zinc with the passage of time. TIlese findings suggested thai biosurfactants producing P. aerllgillosa MF069 166 and Meyerozyma spp. MF 138126 have high potential to be used in different environmental applications and can be considered as su itable candidates for field scale bioremediation studies.