Biosurfactants are produced by a variety of
microorganisms and can be either of low molecular weight type or high-molecular
weight type (known as bioemulsifiers). Biosurfactants have a range of
applications, including in petroleum and cosmetic industries, in medicine and
in bioremediation. When used for bioremediation, biosurfactants can be used to
increase the bioavailability of hydrophobic compounds (e.g. hydrocarbons).
Despite this, they are not used in response to oil spills occurring in the
marine environment, where chemical dispersants are solely used. However, the
toxicity and negative effects of chemical dispersants on the activity of
natural oil-degrading microorganisms has raised concerns.
As biosurfactants are biodegradable and
have low toxicity, they could be used to develop biodispersants and provide an
alternative to chemical dispersants. This has led to an increased interest in
identifying biosurfactant-producing marine microbes that are able to function
in marine ecosystems with low water activity and extreme temperatures. A study
by Raddadi et al. (2017) aimed to identify marine bacteria capable of producing
biosufactants when grown on soybean oil and/or glucose-based media and then
characterise the activity and stability of the biosurfactants produced under
the challenging conditions seen in the marine environment.
Bacteria
collected in marine sediment samples from harbours in southern Italy were
isolated using three successive spreading serial dilutions. Based on colony
morphology, 43 isolated strains were then inoculated in modified mineral salt
medium (mMSM) with either glucose or soybean oil as a carbon source and once bacterial
growth had occurred the cell-free culture supernatants were collected using
centrifugation. The supernatant was then filter-sterilised and screened for
biosurfactant/bioemulsifiers (BS/BE) production by measuring emulsification
activity, drop collapse and interfacial surface tension; 26 isolates were found to
produce BS/BE when grown with glucose while 16 of these isolates were found to
produce BS/BE when grown on soybean oil (a cheap and readily available source
of carbon) with the results suggesting that mainly bioemulsifiers were produced.
Identification of the 26 BS/BE-producing isolates using 16S rRNA sequencing
showed the isolates belonged to the genera Bacillus, Thalassospira, Halomonas and Marinobacter. The BS/BE produced by the isolates
were found to be active and stable at extreme temperatures and low water
activity, reflecting the challenging conditions of the marine environment, as
well as up to 30 months of incubation. The BS/BE were also shown to have good
environmental compatibility as they exhibited low toxicity and were capable of
dispersing crude oil in artificial marine water. Based on their
findings, the authors conclude that the nonpathogenic Marinobacter sp. are suitable for
large-scale BS/BE production.
In summary, the authors identified a range of marine bacteria capable
of producing BS/BE which were active and stable under the challenging
conditions seen in the marine environment and were also environmentally compatible;
the nonpathogenic Marinobacter sp. was suggested to be the most suitable
option for large-scale BS/BE production. The results of this study are
promising as an alternative to chemical dispersants. However, the statement
that the BS/BE produced by the isolates have low toxicity and thus good
environmental compatibility is perhaps premature as the only measure of toxicity
was the effect on bioluminescence of Vibrio fischeri; only having one
measurement of toxicity could be misleading as other measures may produce
different results and so presents a possible limitation of this study and an
area that requires further research.
Reviewed paper:
Raddadi, N., Giacomucci, L., Totaro, G., & Fava, F. (2017).
Marinobacter sp. from marine sediments produce highly stable surface-active
agents for combatting marine oil spills. Microbial cell factories, 16(1), 186.
Hi Georgia,
ReplyDeleteThank you for your interesting review on this paper! I certainly agree that the use of biosurfactant producing microbes is a much better solution for clearing up oil spills than the use of chemical dispersants.
I have read a paper which might be of some interest to you as it also looks at the bioremediation of an oil spill in Italy, but focusses on the fungal community as it has recently been found that fungi can produce biosurfactants too. It is called "The culturable mycobiota of a Mediterranean marine site after an oil spill: isolation, identification and potential application in bioremediation. Bovio et al. (2017)".
Many thanks,
Sophie
Hi Sophie,
ReplyDeleteThank you for pointing me towards this paper, it was a very interesting read and biosurfactants are definitely an exciting area of research.
Thank you,
Georgia