Rhamnolipids Characteristics, Production, Applications, and Analysis - Biosurfactants: Research Trends and Applications - page 61

of the early rhamnolipid producers. This strain is able to produce rhamnolipids
containing fatty acyl chains with 14 carbons in length. Haussler et al. (1998) stated
that B. pseudomallei is able to produce a heat-stable toxin and is resistant against
alkaline and acidic conditions. They also reported about the production of dirham-
nolipids (Rha-Rha-C 14 -C 14 ) with a molecular mass of 762 Da.
Burkholderia glumae
Costa et al. (2011) conducted some experiments on rhamnolipid production by
B. glumae AU6208, a gram-negative soil bacterium, on canola oil as the carbon
source and urea as the nitrogen source. Their experiments verified that B. glumae,
a pathogen member of Burkholderia genus, is able to produce substantial quantities
of rhamnolipids. They reported that after 7 days, 1000.7 mg/L of rhamnolipids were
produced with a CMC of 25-27 mg/L, and they were able to reduce the interfacial
tension of hexadecane from 40 to 18 mN/m. The produced rhamnolipids also demon-
strated exceptional emulsifying properties for long-chain alkanes. The rhamnolipids
produced by B. glumae consisted of a variety of mono-and dirhamnolipid congeners,
but the main portion of the mixture is made of dirhamnolipids (Rha-Rha-C 14 -C 14 ).
It has been reported that the side chains in these rhamnolipids varied between
C 12 -C 12 and C 16 -C 16 and are much longer than the one produced by P. aeruginosa .
Moreover, the produced rhamnolipids showed excellent surface-active properties.
Burkholderia plantarii
Hoermann et al. (2010) studied the rhamnolipid production by B. plantarii DSM
9509(T), a gram-negative soil bacterium. Their experiment showed that when they
used glucose as the only source of carbon, 45.74 mg/L of rhamnolipids were obtained.
Their analysis showed that the structure of produced rhamnolipids by B. plantarii
DSM 9509(T) was different from the ones produced by P. aeruginosa . It was mainly
made by rhamnolipid Rha(2)-C 14 -C 14 , and its CMC was between 15 and 20 mg/L,
and it was able to lower surface tension of distilled water to 29.4 mN/m. Vatsa
et al. (2010) stated that B. plantarii is able to produce heat-stable dirhamnolipids
(Rha-Rha-C 14 -C 14 ), which are structurally similar to the rhamnolipids produced
by P. aeruginosa and are able to stimulate mononuclear cells in human to produce
tumor necrosis factor.
Burkholderia thailandensis
Dubeau et al. (2009) conducted some experiments on the process of rhamnolipid
production by noninfectious, gram-negative bacteria, B. thailandensis . It has been
indicated that B. thailandensis carries the genes (rhlA, rhlB, and rhlC) responsible
for the rhamnolipid synthesis (Dubeau et al., 2009; Toribio et al., 2010). Therefore,
it is expected that these bacteria produce rhamnolipids using similar pathways as
P. aeruginosa , and the produced rhamnolipid's structures would be similar, although
it has been indicated that B. thailandensis had the ability to produce rhamnolipids
with long side chains containing 3-hydroxy fatty acid moieties as opposed to the
short-chain rhamnolipids produced by P. aeruginosa .
The rhamnolipids produced by B. thailandensis were mainly composed of dir-
hamnolipids, and the minor portion of the mixture is made of monorhamnolipids.