Trehalose Biosurfactants - Biosurfactants: Research Trends and Applications - page 204

C arBon s ourCe anD G rowth C onDitions
It was assumed that the alkanothrophic Rhodococcus strains respond specifically
to the presence of hydrocarbons in the medium by producing cell-bound trehalose
lipid surfactants (Lang and Philp 1998). Several studies were conducted confirm-
ing this capability. For example, we tested various hydrocarbons as substrates for
Rhodococcus wratislaviensis biosurfactant production and found that strain BN38
was able to utilize n -alkanes ranging from n -octane to n -heptadecane (Table 8.1).
Short-chain n -alkanes (C 5 -C 7 ) were not able to support growth and only after
n -undecane the organism produced significant amounts of biomass and biosurfactant
with the surface tension lowered to 29-32 mN m −1 . Surfactant concentration reached
the maximal level of 3.1 g L −1 on hexadecane. Similar results were obtained by Philp
et al. (2002) with the alkanotrophic strain Rhodococcus ruber IEGM 231. The sur-
factant production of R. ruber increased with the increase in n -alkanes chain length.
Thus, during growth on undecane and dodecane, the surfactant concentrations were
minimal, but increased from 1.8-2.2 g L −1 on tridecane and tetradecane, to 4.0 g L −1
on pentadecane, reaching its maximal level of 9.9 g L −1 on hexadecane. Haddadin
et al. (2009) tested four carbon sources (diesel, naphtalene, crude oil, and benzene)
and found that biosurfactant production of R. erythropolis and R. ruber strains was
optimal on naphthalene and diesel oil. More recently, some authors reported the
production of extracellular trehalose lipids from n -alkanes. Thus, Rhodococcus sp.

TABLE 8.1
Growth and Surfactant Production of R. wratislaviensis BN38
on n -Alkanes

Surfactant
Concentration (g L −1 )

Growth Substrate Biomass (g L −1 ) Surface Tension (mN m −1 )

Pentane — 59.0 —

Hexane — 62.0 —

Heptane — 62.0 —

Octane 0.54 40.3 0.05

Nonane 0.73 39.0 0.15

Decane 0.86 35.0 1.50

Undecane 0.90 32.0 0.75

Dodecane 1.65 23.3 1.20

Tridecane 1.53 29.0 1.20

Tetradecane 1.80 30.2 1.50

Pentadecane 2.30 29.0 1.85

Hexadecane 3.35 28.4 3.10

Heptadecane 2.54 29.0 2.75

Source: Tuleva, B., Christova, N., Cohen, R., Stoev, G., and Stoineva, I.: Production and structural
elucidation of trehalose tetraester (biosurfactant) from a novelalkanothrophic alkanothrophic
Rhodococcus wratislaviensis strain. J. Appl. Microbiol . 2008. 104. 1703-1710. Copyright
Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.