Environmental Engineering Reference
In-Depth Information
cyclooctane, toluene, carbon tetrachloride,
dichloromethane, cottonseed, jojoba and ground-
nut oil at 1 mg mL
−1
. The inherent properties
of the biosurfactant make it a potential candidate
for bioremediation of oil and hydrocarbons.
However,
Cronobacter sakazakii
is a Gram-
negative pathogenic bacterium (Lai
2001
),
reported as the cause of meningitis bacteraemia,
necrosis and enterocolitis in infants. Infections
have been associated with the use of powdered
infant formula contaminated with the bacterium
(Bowen and Braden
2006
; CDC
2002
).
The industrial application of pathogenic bio-
surfactant producers is clearly problematic
based on the pathogenic effects of the organisms
and their products on humans and animals.
Additionally, some of these pathogens exhibit
multidrug resistance and have recorded high
mortality rates from their associated diseases.
Therefore, they are now considered as potential
biological warfare agents and as such are not
potential biological models for industrial bio-
technological processes (Walter
2009
). For this
combination of security and health reasons,
there is a need to develop industrial processes
based on nonpathogenic biosurfactant-produc-
ing strains.
biosurfactant types identifi ed to date have been
reported (Table
2
).
3.1
Rhamnolipids
Novel natural producers of rhamnolipids identi-
fi ed as
P. clemancea
nov. and
P. teessidea
nov.
have been reported by Rahman et al. (
2010
).
Rhamnolipid production can be achieved with
Pseudomonas
sp. other than
P. aeruginosa.
Pseudomonas fl uorescens
is a nonpathogenic
Gram-negative, rod-shaped bacterium that has
been found to produce biosurfactants as well as
useful enzymes (cellulase, pectinase), self-
defence factors (hydrogen cyanide), siderophores
(pyochelin, pyoverdine), antibiotics (pyrrolnitrin,
pyoluteorin) and 2,4-diacetylphloroglucinol, a
molecule that can break down plant-derived car-
bohydrates, enhance host immune mechanisms
and inhibit phytopathogens and bacteriophages
(Stover et al.
2000
; Paulsen et al.
2005
). This
organism has been reported as a degrader of cer-
tain environmental pollutants such as styrene,
TNT and polycyclic aromatic hydrocarbons and
as a result has been employed in many bioreme-
diation processes.
The production of a thermostable rhamnolipid
biosurfactant with excellent foaming and emulsi-
fying stability by
P. fl uorescens
was reported by
Abouseoud et al. (
2007
). The biosurfactant was
stable at 100 °C and retained its positive effect on
surface tension (34-30 mN m
−1
) even at high pH
values. Stoimenova et al. (
2009
) isolated from
industrial wastewater
P. fl uorescens
HW-6 capa-
ble of producing rhamnolipid biosurfactants at
relatively high levels on various carbon substrates
including hexadecane, vegetable oil, mineral oil
and glycerol. The culture supernatant of the strain
exhibited a reduction in surface tension to
28.4 mN m
−1
. Vasileva-Tonkova et al. (
2006
) also
reported production of rhamnolipid biosurfactant
by
P. fl uorescens
HW-6 at concentrations of
14-20 g L
−1
on hexadecane and interfacial tension
of 35 mN m
−1
, possessing a low critical micelle
concentration value of 20 mg L
−1
. Recently, a
rhamnolipid exhibiting high antimicrobial
3
Biosurfactant Production
Using Nonpathogenic
Organisms
Recently, due to the health and safety issues asso-
ciated with some biosurfactant-producing strains,
research towards identifying new nonpathogenic
producers and biotechnological production of
biosurfactants using recombinant/mutant strains
has been given more attention. The advantages
of using nonpathogenic organisms may include
production of biosurfactants with various con-
gener species, including the possibility of bio-
surfactants with less or no cytotoxic effects on
living cells, and disconnection of their synthetic
pathways from complex mechanisms such as
quorum sensing in rhamnolipid synthesis.
Nonpathogenic natural producer strains and their
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