Environmental Engineering Reference
In-Depth Information
excrete biosurfactant into their medium.
Biosurfactant production has also been reported
for nonpathogenic
L. delbrueckii
by Thavasi
et al. (
2011a
). This organism showed maximum
glycolipid production of 5.35 mg L
−1
at 144 h
incubation with peanut oil cake as substrate, but
higher production was recorded after the station-
ary phase of growth. This was thought to be due
to the release of cell-bound biosurfactant in the
early stationary phase. In addition,
L. delbrueckii
could maximally degrade 61.25 % crude oil in
the presence of fertilisers; hence the organism is
both a biosurfactant producer and a hydrocarbon
degrader. Lactobacilli are probiotics and non-
pathogenic organisms designated “Generally
Recognized as Safe” (GRAS) by the American
Food and Drug Administration (FDA). The
organism's ability to utilise lactose instead of
glucose via an alternative metabolic pathway for
biosurfactant synthesis has proven them as ideal
hosts for biotechnological techniques especially
metabolic engineering towards large-scale pro-
duction of cell-bound biosurfactants (Rodrigues
et al.
2006c
). Although the biosurfactant yield by
these organisms is low, optimisation of culture
conditions may improve their production.
Rhodococcus
sp. are a group of aerobic, non-
sporulating, Gram-positive bacteria that can be
found in a wide range of environments. They are
usually considered as experimentally advanta-
geous due to their high growth rate and simple
developmental cycle. These organisms are
effective for the degradation of aromatic hydro-
carbons, production of bioactive steroids,
bio-desulphurisation of fossil fuel and biocon-
version of waste products to valuable com-
pounds (McLeod and Eltis
2008
). Strains of
these species have been reported as biosurfac-
tant producers including
R. erythropolis
IMV
Ac-5017 (Pirog et al.
2013
) and
Rhodococcus
sp. MTCC 2574 (Mutalik et al.
2008
).
Furthermore, Pacheco et al. (
2010
) have identi-
fi ed
Rhodococcus erythropolis
ATCC 4277 is a
producer of a biosurfactant exhibiting excellent
enhanced oil desorption from an oil shale.
Rhodococcus ruber
Z25 identifi ed by 16 rDNA
sequencing produced cell growth-associated
biosurfactants on n-hexadecane with maximum
yield of 13.34 g L
−1
at 44 h (Zheng et al.
2009
).
Rhodococcus
spp. produce surface-active treha-
lose lipids, and reports have shown that these
surface-active compounds present interesting
physico-chemical and biological properties.
Trehalose lipids can signifi cantly reduce the
surface tension of water from 70 mN m
−1
to
30.8 mN m
−1
(Mutalik et al.
2008
) and can form
microemulsions (Zaragoza et al.
2013
). In addi-
tion, trehalose lipids have been reported to
inhibit protein kinase activity in vivo (Isoda
et al.
1997
) and induce the cell lysis of
E. coli
IEM-1 as well as the vegetative and spore cells
of
Bacillus subtilis
BT-2 (Pirog et al.
2013
).
They have also been found useful in soil biore-
mediation and microbial enhanced oil recovery
(Philip et al.
2002
; Bell et al.
1998
). This group
of bacteria is considered as an ideal host for bio-
technological production of non-toxic biosur-
factant on industrial scales because of their
genetic and catabolic diversity (associated pre-
sumably with their large chromosome and three
large linear plasmids (van der Geize and
Dijkhuizen
2004
; McLeod et al.
2006
). These
organisms are usually nonpathogenic with only
two species
R. fascians
and
R. equi
(Goethals
et al.
2001
) identifi ed as plant and animal patho-
gens as well as causing infections in immune-
compromised individuals. Nonpathogenic
biosurfactant producers and their biosurfactants
are shown in
Table 2
.
3.3
Lipopeptides
and Phospholipids
Biosurfactants other than glycolipids produced
by nonpathogenic organisms have been docu-
mented in literature.
Bacillus subtilis
is a ubiqui-
tous Gram-positive rod-shaped bacterium, found
commonly in water, soil and air, and contributes
to nutrient cycling in the environment. This
organism is industrially useful as it is one of the
most widely used bacteria in the production of
enzymes (amylases, proteases, inosine, ribosides
and amino acids) and speciality chemicals including
biosurfactants (Erikson
1976
). This bacterium
has also been shown to produce a variety of
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