Rhamnolipids Characteristics, Production, Applications, and Analysis - Biosurfactants: Research Trends and Applications - page 60

high salinity environment (up to 10% NaCl) and exposure to a wide range of pH.
Following the investigations of Abouseoud et al. (2008a) on rhamnolipid produc-
tion by P. fluorescens Migula 1895-DSMZ, using olive oil as the sole carbon and for
5 days at ambient temperature and at neutral pH showed that after 40 h, the values
of surface tension of supernatant reached 30 mN/m with an emulsification of 67%,
but after 72 h, its surface tension was 35 mN/m and emulsification reached to 62%.
Furthermore, results from the investigations of Abouseoud et al. (2010) on the pro-
duction of rhamnolipids by P. fluorescens Migula 1895-DSMZ growing on olive oil
as the carbon source was aligned with results from the past experiments. In their
experiments, the product displayed the CMC of 290 mg/L, and it was stable at higher
pH and showed resilience toward high salinity.
P seudomonas alcaligenes
P. alcaligenes is a gram-negative, aerobic, motile bacterium that is found in soils.
Oliveira et al. (2009) are the pioneers in research on the production of rhamnolipids
by P. alcaligenes by using palm oil as the sole carbon source. For their experiments,
they isolated the strain of P. alcaligenes polyepsilon-caprolactone (PCL) from crude
oil-contaminated soil. They conducted some experiments by varying the palm oil
concentration (0.5% and 5.5%, v/v), with initial pH of the media (6 and 8), as well as
the agitation rate (80 and 220 rpm). Their experiment showed that change in the con-
centration of palm oil has the highest effect on the rhamnolipid production; on the
other hand, agitation could slightly affect the oil biodegradation, and varying pH had
no effect on the production. It has been shown that the rhamnolipid mixture produced
by the P. alcaligenes strain consisted of four types of dirhamnolipids and two types
of monorhamnolipids. The product had the CMC value of 30 mg/L and decreased
the surface tension of substrate (palm oil) to 31 mN/m. They observed the emulsi-
fication of more than 55% for crude oil after 72 h. Their results revealed that the
P. alcaligenes strain is a rhamnolipid producer. These bacteria can be used in in situ
treatment of polluted soils and for many other environmental applications.
B urkholderia s trains
The Burkholderia genus used to be a branch of Pseudomonas genus and was classi-
fied as the same genus until 1992, before the analysis of their rRNA sequence showed
that they belong to two different genera. Still they share many of the physiochemi-
cal characteristics such as the ability to produce rhamnolipids (Abdel-Mawgoud
et al., 2011). Furthermore, Abdel-Mawgoud et al. (2011) introduced some less known
but nonpathogenic strains of Burkholderia that are able to produce rhamnolipids,
strains such as B. glumae, B. plantarii , and B. thailandensis .
Burkholderia pseudomallei
B. pseudomallei is a gram-negative, aerobic, pathogenic, motile, and nonspore-forming
bacteria that can be found in contaminated soil, water, and fruits. This bacte-
rium could live in nutrient-depleted and also highly acidic environment (Pathema,
2006). According to Gunther et al. (2006), this pathogenic strain is known as one