Environmental Engineering Reference
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activities on both Gram-positive and Gram-negative
pathogenic strains - Listeria monocytogenes ,
Staphylococcus aureus , methicillin- resistant
S. aureus , E. coli , Salmonella typhimurium and
Candida albicans - has been reported to be pro-
duced from Pseudomonas fl uorescens MFS03
(Govindammal and Parthasarathi 2013 ). The bio-
surfactant was effective as a surface and emulsi-
fying agent and could have potential applications
in the bioremediation of hydrocarbon-polluted
sites. Rhamnolipid production was also reported
for nonpathogenic P. chlororaphis (Gunther et al.
2005 ) and P. putida BD2 (Janek et al. 2013 ).
Dubeau et al. ( 2009 ) reported production of
0.4-1.5 g L −1 rhamnolipid by Burkholderia thai-
landensis at 34 °C with 4 % glycerol or canola oil
in nutrient broth. B. thailandensis is a Gram-
negative, mesophilic bacterium closely related to
B. pseudomallei but rarely causes infections in
humans or animals (Wuthiekanun et al. 1996 ;
Smith et al. 1997 ; Lertpatanasuwan et al. 1999 ).
The lethal inoculum size for B. thailandensis is
approximately 1,000 times higher than that for B.
pseudomallei (Joost Wiersinga et al. 2008 ). This
organism does not require biosafety level 3 con-
ditions and has no restriction on the use of antibi-
otics or resistance markers for its genetic
manipulation. The organism is not considered as
a biosecurity threat and therefore is a potential
industrial tool (Haraga et al. 2008 ; Glass et al.
2006 ). Recently, Hošaková et al. ( 2013 ) identi-
fi ed Enterobacter asburiae as nonpathogenic
rhamnolipid producers. Rezanka et al. ( 2011 )
reported on three novel rhamnolipid-producing
organisms and were identifi ed as Thermus sp.,
Thermus aquaticus and Meiothermus ruber .
These organisms have been categorised as bio-
safety level 1 organisms and are not pathogenic
to humans. Pantazaki et al. ( 2010 ) have reported
the simultaneous production of polyhydroxyal-
kanoates (PHAs) and rhamnolipids by a non-
pathogenic thermophilic bacterium Thermus
thermophilus HB8 (DSM 579) cultivated in min-
eral salt medium at 75 °C using glucose and
sodium gluconate as sole carbon sources. Other
new nonpathogenic rhamnolipid producers
include Enterobacter hormaechei PTCC 1799
(Rabiei et al. 2013 ), Tetragenococcus koreensis
(Lee et al. 2005 ) and Pseudoxanthomonas sp.
(Nayak et al. 2009 ).
3.2
Glycolipids
The Streptococcus thermophilus bacterium is
used widely in the dairy industries for the produc-
tion of yogurt and cheese and is considered as
benefi cial to health since it aids digestion of dairy
products in lactose-intolerant individuals (Kiliç
et al. 1996 ; Hutkins 2002 ; Taylor and Mitchell
2007 ). According to Busscher et al. ( 1997 ), a bio-
surfactant released from S. thermophilus was used
in the control of fouling of heat-exchanger plates
in pasteurisers because it inhibited the colonisa-
tion of other thermophilic and pathogenic strains
of Streptococcus responsible for fouling. Two
probiotic bacteria Lactococcus lactis 53 and
S. thermophilus A have been identifi ed as produc-
ers of cell-bound biosurfactants at the stationary
growth phase in the presence of lactose and cheese
whey as carbon substrates (Rodrigues et al. 2006a ,
b ). A protein-containing biosurfactant from
Lactobacillus acidophilus has also been demon-
strated to reduce the adhesion and biofi lm forma-
tion of Streptococcus mutans on glass slides
(Tahmourespour et al. 2011 ), indicating that the
treatment of teeth with this biosurfactant may be
an alternative dental control for biofi lm develop-
ment and adhesion of the pathogens on teeth.
Similarly, Gudiña et al. ( 2011 ) investigated
the production of cell-bound and excreted biosur-
factant by three lactobacilli strains and
Leuconostoc mesenteroides strains. The lactoba-
cilli strains were L. coryniformis sp. torquens
CECT 25600, L. paracasei sp. paracasei A20
and L. plantarum A14. The studies revealed a
decrease in surface tension of the culture broth
for all the strains after 72 h incubation and the
surface tension ranged from 1.4 to 6.4 mN m −1 .
The highest excreted biosurfactant rate was
recorded for L. paracasei sp. paracasei A20 with
surface tension of 6.4 mN m −1 . However, the level
of cell-bound biosurfactant was found to be
higher than that of excreted molecules for all the
strains. This is in contrast to other microorganisms
such as Pseudomonas and Bacillus that primarily
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