1 Stimulation of rhamnolipid biosurfactants production in Pseudomonas 2 aeruginosa AK6U by organosulfur compounds provided as sulfur 3 sources 4 Wael Ismail a, * Q1 , Sultanah A.L. Shammary a , Wael S. El-Sayed b,1 , Christian Obuekwe c , 5 Ashraf M. El Nayal a , Abdul Salam Abdul Raheem a , Abdulmohsen Al-Humam d 6 a Life Sciences Department, Q2 Biotechnology Program, College of Graduate Studies, Arabian Gulf University, Manama, Bahrain 7 b Taibah University, Faculty of Science, Biology Department, Al-Madinah Al-Munawarah, 344, Saudi Arabia 8 c Department of Biological Sciences, College of Science, Kuwait University, Kuwait 9 d Research & Development Center, P.O. Box 62, Dhahran, Saudi Aramco, Saudi Arabia A R T I C L E I N F O Article history: Received 1 December 2014 Received in revised form 21 February 2015 Accepted 2 March 2015 Available online xxx Keywords: Surface tension Biodesulfurization Dibenzothiophene A B S T R A C T A Pseudomonas aeruginosa AK6U strain produced rhamnolipid biosurfactants to variable extents when grown on MgSO 4 or organosulfur compounds as sulfur sources and glucose as a carbon source. Organosulfur cultures produced much higher biosurfactants amounts compared to the MgSO 4 cultures. The surface tension of the growth medium was reduced from 72 mN/m to 54 and 30 mN/m in cultures containing MgSO 4 and 4,6-dimethyldibenzothiophene (4,6-DM-DBT), respectively. AK6U cultures produced different rhamnolipid congener profiles depending on the provided sulfur source. The dibenzothiophene (DBT) culture produced more diverse and a higher number of rhamnolipid congeners as compared to the DBT-sulfone and MgSO 4 cultures. The number of mono-rhamnolipid congeners in the DBT culture was also higher than that detected in the DBT-sulfone and MgSO 4 cultures. Di-rhamnolipids dominated the congener profiles in all the analyzed cultures. The sulfur source can have a profound impact on the quality and quantity of the produced biosurfactants. ã2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). 10 1. Introduction 11 Biosurfactants are amphiphilic tensioactive natural products 12 produced by a diversity of microorganisms [16,39]. They are 13 capable of reducing the surface and interfacial tension [39]. 14 Moreover, effective biosurfactants are characterized by their ability 15 to enhance the aqueous solubility of hydrophobic compounds and 16 to emulsify hydrocarbons in water [16]. As compared to petro- 17 leum-based (synthetic) surfactants, biosurfactants are environ- 18 mentally compatible, less or non-toxic, more efficient, stable under 19 extreme conditions and can be produced from inexpensive 20 renewable substrates [38]. These advantages render biosurfac- 21 tants, interesting biotechnological products that have various 22 applications, and are likely to replace synthetic surfactants in the 23 future [16,36]. 24 Environmental applications of biosurfactants include bioreme- 25 diation and soil washing. They can also be applied in various 26 processes in the oil industry such as microbial enhanced oil 27 recovery, upgrading of crude oil, clean-up of oil containers and 28 storage tanks, and formulation of petrochemicals [34]. Biosurfac- 29 tants also offer many interesting biomedical and agricultural 30 applications [9,30]. The commercialization of biosurfactants has 31 been impeded by the high production costs and low yield of the 32 producing strains. There is ongoing research and development 33 work aiming to improve the economics of the biosurfactant 34 production process. This can be achieved by optimizing various 35 aspects like the yield, the growth conditions, the downstream 36 processing, etc. [24]. 37 Many studies have investigated the effect of the carbon source 38 in the growth medium on biosurfactants production by some 39 microorganisms. Both the type and concentration of the carbon 40 source were shown to be essential determinants of biosurfactants 41 yield and physicochemical properties. Hydrophobic carbon sour- 42 ces were found to be superior to hydrophilic ones in promoting 43 biosurfactants production [1,33,37]. Other growth medium com- 44 ponents that were found to have an impact on biosurfactants * Corresponding author. Tel.: +973 36146948; fax: +973 17239664. E-mail address: waelame@agu.edu.bh (W. Ismail). 1 Permanent address: Ain Shams University, Faculty of Science, Microbiology Department, 11566 Cairo, Egypt. http://dx.doi.org/10.1016/j.btre.2015.03.001 2215-017X/ ã 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Biotechnology Reports xxx (2015) xxx–xxx G Model BTRE 79 1–9 Please cite this article in press as: W. Ismail, et al., Stimulation of rhamnolipid biosurfactants production in Pseudomonas aeruginosa AK6U by organosulfur compounds provided as sulfur sources, Biotechnol. Rep. (2015), http://dx.doi.org/10.1016/j.btre.2015.03.001 Contents lists available at ScienceDirect Biotechnology Reports journal homepage: www.else vie r.com/locat e/btre