Trehalose Biosurfactants - Biosurfactants: Research Trends and Applications - page 206

and R. ruber strains producing nonionic glycolipids (Rapp et al. 1979; Philp et al.
2002; Haddadin et al. 2009). The formation of trehalose-2,2′,3,4-tetraesters was
favored both by nitrogen limitation and temperature shift from 30°C to 22°C dur-
ing growth of R. erythropolis DSM432215 on hydrocarbons (Ristau and Wagner
1983). Trehalose-2,2′,3,4-tetraester production was growth-linked in a biosurfactant-
producing Rhodococcus sp. 51T7 (Espuny et al. 1996), while the extracellular accu-
mulation of mono- and disuccinoyl trehalose lipids by a strain R. erythropolis SD -74
was evidently not growth-associated (Uchida et al. 1989b). Kim et al. (1990) used both
nitrogen limitation and resting cells for enhanced synthesis of an anionic tetraester
during cultivation on n -alkanes and the successful conversion of the technical grade
C10 n -alkane into more than 20 g L −1 of trehalolipids.
o Ptimization of P roDuCtion
According to Mukherjee et al. (2006), a large number of biosurfactant producers
belonging to the genera Rhodococcus , Gordonia , and Acinetobacter have not yet been
exploited properly for the economic production of naturally occurring surface-active
compounds. This refers particularly to trehalose lipids that are often cell-bound; there-
fore, product recovery costs increase and production yields are low. Some practical
approaches have been adopted with the aim of reducing biosurfactant production costs:
(1) use of cheap and waste substrates, (2) bioprocess development including optimal pro-
duction and recovery, (3) development of overproducing strains (Mukherjee et al. 2006).
As pointed earlier, there are still limited attempts for reducing production costs
by using cheap substrates for trehalose lipid production. However, recent publica-
tions proved that rhodococci could grow well on vegetable oils and successfully
produced biosurfactants. Thus, Sadouk et al. (2008) reported that R. erythropolis
16 LM.USTHB, grown on residual sunflower frying oil, produced extracellular gly-
colipids, lowering in their crude form the surface tension of water until 31.9 mN m −1 .
Ruggeri et al. (2009) isolated Rhodococcus sp. BS32 capable of producing extracel-
lular biosurfactants on rapeseed oil.
Several studies are focused on optimization of the cultural factors affecting
biosurfactant production. For example, Uchida et al. (1989) reported that the pro-
duction of succinoyl trehalose lipids in R. erythropolis SD-74 was optimized at
high concentration of phosphate buffer and neutral pH and a yield of 40 g L −1 was
achieved. Improvement of the cultivation conditions (oxygen supply, pH) and usage
of 100 g L −1 technical grade C10 n -alkane resulted in a yield of 32 g L −1 trehalos-
elipid in 20 L bioreactor (Kim et al. 1990). Espuny et al. (1996) optimized sodium
nitrate, potassium phosphate, and iron concentration, and the production of trehalose
tetraester by Rhodococcus strain 51T7 increased from 0.5 to 3.0 g L −1 . More recently,
the production of biosurfactant from Rhodococcus spp. MTCC 2574 was effec-
tively enhanced by response surface methodology (Mutalik et al. 2008). The yield
of biosurfactant before and after optimization was 3.2 and 10.9 g L −1 , respectively.
Franzetti et al. (2009) applied a steepest ascent procedure and a Central Composite
Design to obtain a second-order polynomial function fitting the experimental data
near the optimum. In the optimized cultural condition, they obtained a fivefold
increase in the biosurfactant concentration compared to the unoptimized medium.