Application of the biosurfactants produced by Bacillus spp. (SH 20 and SH 26) and Pseudomonas aeruginosa SH 29 isolated from the rhizosphere soil of an Egyptian salt marsh plant for the cleaning of oil - contaminataed vessels and enhancing the biodegradation of oily sludge

Abstract

During the screening for biosurfactant-producing bacteria isolated from the rhizosphere soil of an Egyptian salt marsh plant, three bacterial strains (Bacillus spp. SH 20 and SH 26, and Pseudomonas aeruginosa SH 29) were most active strains. Biosurfactants produced by the three bacterial strains were stable at wide range of pH (1 to 14), wide range of temperature (0 to 121°C) and salinity (5 to 15% NaCl). The two Bacillus species were able to produce high E24 values for petroleum oil (75 to 84.4%), while P. aeruginosa was able to produce E24 value of 62%. Accordingly, the sterilized broth culture (supernatants) containing the biosurfactants produced by the two Bacillus spp. were used for enhancing the bioremediation of oily sludge-contaminated soil. On the other hand, the sterilized supernatant of P. aeruginosa was applied for cleaning oil-contaminated vessels. The results show that addition of the supernatant of Bacillus sp. SH 26 stimulated the biodegradation of the oily sludge (34.0% w/w); this is in contrast to biodegradation of 28.0 and 22.2% of the oil in presence of uninoculated medium and the supernatant of Bacillus sp. SH 20. When the contaminated soil was treated with the mixture of the two supernatants of the two Bacillus spp., no biodegradation of the oil above 26.3% was observed. This may indicate inhibitory effect on some of the oil degraders present in this system, due to the presence of the biosurfactant produced by Bacillus sp. SH 20. When the phytogenic biosurfactant was applied as a comparison, it was of interest to find that this biosurfactant was able to degrade 53.8% of the oil, and this represent excellent candidate for enhancing bioremediation of oil contaminated sites. This was followed by the microbial biosurfactant (34%) produced by Bacillus sp. SH 26. The results of cleaning oil-contaminated vessels by applying the supernatant of P. aeruginosa SH 29 show that after 15 min of the addition of the supernatant, the oil was recovered from the bottom and walls of the vessels and floated on the supernatant as a distinct phase. This indicates that the sterilized supernatant of P. aeruginosa SH 29 can be used directly for cleaning oil storage tanks and other vessels used for transportation and storage of crude petroleum oil. Key words: Biosurfactants, Pseudomonas aeruginosa, Bacillus sp., bioremediation, cleaning oil-contaminated vessels