Preprint volume - SIBM

Pre-print Volume - Posters
VARIOUS TOPICS
Reduction of surface tension (ST) was determined with a digital tensiometer TSD
(Gibertini), according to Wilhelmy method. Further techniques were performed as
Bacterial Adhesion To Hydrocarbons (BATH) assay, hemolysis of erythrocytes by
rhamnolipids (Blood Agar Test). Finally C-TAB Agar Plate Assay was performed to
all strains, a semi-quantitative assay for detection of extracellular glycolipids or other
anionic surfactants production.
Results – Pseudomonas strains showed best growth on glucose and vegetable oil as
carbon source. Corresponding to the maximum value of OD600 on glucose as carbon
source, 100% of emulsifying activity was measured, and an E24 index value of 30%
was detected. Lower values of OD600 were observed on tetradecane and soybean oil as
substrates in relation to a lower emulsifying activity (75 and 60% respectively).
Acinetobacter strain gave better results on soybean oil and tetradecane, showing values
of emulsifying activity between 80 and 40%, accompanied by a reduction of surface
tension after only 48 hours with a value of 19.7 mN/m on soybean oil. Pseudomonas
strains had a higher hydrophobicity (BATH) in comparison to Acinetobacter.
Biosurfactants produced by every tested strains had hemolytic activity, confirmed by a
clear or green zone (β or α-hemolysis) on a blood agar plate. The only positive result
recorded on C-TAB Agar Plate Assay was obtained by a Pseudomonas sp. strain grown
with vegetable oil as carbon source.
Conclusions – The production of the biosurfactant was found to be a function of cell
growth, with maximum production occurring during the exponential phase.
All the strains produced emulsion, but only a Pseudomonas sp. was able to gave a
stable emulsion. Acinetobacter sp. was the better strain for biosurfactant production but
was unable to metabolize glucose, while Pseudomonas strains degrade in an optimal
way all the substrates, as confirmed by the BATH test results. Biosurfactants showed
hemolytic activity, and a Pseudomonas sp. strain gave positive result for anionic
surfactant production. Finally, we can assume that use of soybean oil as substrate in the
culture medium represents a good alternative at lower cost to improve further
application. However, could be useful increase studies in this field.
References
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KITAMOTO D., ISODA H., NAKAHARA T. (2002) - Functions and Potential Applications of
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Bioscience and Bioengineering, 94 (3): 187-201.
MUKHERJEE S., DAS P., SEN R. (2006) - Towards commercial production of microbial surfactants.
Biotech., 24 (1): 509-515.
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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