Environmental Engineering Reference
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two nonpathogenic species such as C. kutscheri
and C. alkanolyticum ATCC 21511, respectively
(Thavasi et al. 2007 ; Crosman et al. 2002 ).
Halomonas contained high levels of K, Ca, Mg
and several trace metals such as Zn, Cu, Fe and
metalloid Si and has the specifi c ability to bind
Ca, Si, Fe, Mn, Mg and Al in marine sediments.
Furthermore, the growth of marine diatom
Thalassiosira weissfl ogii was enhanced in the
presence of purifi ed EPS or to marine sediments
exposed to EPS, indicating that the trace metals
bound to the EPS become biologically available
for the diatoms to utilise for growth. This bacte-
rium therefore has the potential for the biotech-
nological development of safe antimicrobial and
anticancer drugs as well as eco-friendly environ-
mental products.
3.4
Heteropolysaccharides
Halomonas are a group of Gram-negative, non-
sporing bacteria usually found in many different
extreme water and soil environments, mainly
saline, hypersaline or alkaline ecosystems. They
belong to the family of Halomonadaceae and are
classifi ed as Gammaproteobacteria currently
made up of 10 genera. They are considered to be
nonpathogenic (von Graevenitz et al. 2000 ) and
are potential industrial microbes due to their abil-
ity to synthesise microbial exopolysaccharides.
Levan and mauran are examples of microbial
polysaccharides from Halomonas spp. with a
considerable market due to their exceptional per-
formance at extreme industrial conditions (Poli
et al. 2009 ; Llamas et al. 2006 .) Although a few
strains have been associated with certain human
infections and contamination in a dialysis centre
(Stevens et al. 2009 ), several Halomonas species
have been classifi ed as nonpathogens and also
identifi ed as biosurfactant producers. According
to Donio et al. ( 2013 ), Halomonas sp. BS4 iso-
lated from solar salt works has produced a het-
eropolysaccharide biosurfactant that suppressed
the proliferation of mammary epithelial carci-
noma cells by 46.77 % at 25
4
Production of Biosurfactant
by Recombinant Strains
Pathogenicity may be avoided by the expression
of biosurfactant production in heterologous
microbial strains and mutants. Rhamnolipids can
be synthesised by nonpathogenic heterologous
strains provided with the rhamnosyltransferase
genes rhlA , rhlB and rhlC . According to Cha
et al. ( 2008 ), nonpathogenic heterologous P.
putida 1067 (pNE2) expressing the rhlABRI gene
from pathogenic P. aeruginosa EMS1 cultured in
the mineral salt medium for 7 days in the pres-
ence of 2 % soybean oil as the sole carbon source
exhibited rhamnolipid productivity that was
greater than that of P aeruginosa EMS1. Scope
remains for optimisation of the production condi-
tions potentially leading to increased biosurfac-
tant production making this organism useful for
industrial biosurfactant production. Furthermore,
Ochsner et al. ( 1995 ) investigated the heterologous
expression of rhlAB in P. fl uorescens , P. putida
and E. coli . The results showed 0.25 g L βˆ’1 , 0.6 g
L βˆ’1 and no rhamnolipid, respectively, for the
organisms, but Wang et al. ( 2007 ) have reported
rhamnolipid production in E. coli BL21 with the
expression of rhlAB operon (Table 3 ).
In another study, rmlBDAC operon involved in
dTDP- L -rhamnose biosynthesis was introduced
into E. coli W3110 in addition to rhlAB operon,
and a total fi nal concentration of 120.6 mg L βˆ’1
mono-rhamnolipid was achieved using glucose as
L concentration. In
addition, the pure biosurfactant exhibited
antibacterial activity on Staphylococcus aureus ,
Klebsiella pneumoniae , Streptococcus pyogenes
and Salmonella typhi and antifungal activity on
Aspergillus niger , Fusarium sp., Aspergillus
fl avus and Trichophyton rubrum . The biosurfac-
tant was also found to display antiviral activity on
white spot syndrome virus at high percentage
(60, 80 and 100 %) and effectively suppressed the
pathological effect of the virus. Gutierrez et al.
( 2013 ) have also shown the signifi cance of
exopolysaccharide (EPS) produced from marine
Halomonas sp. TG39 in trace metal biogeochem-
ical cycling. Calvo et al. ( 2002 ) have also docu-
mented the production of EPS from Halomona
eurihalina . This research revealed that EPS from
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