P. aeruginosa PAO1 releases a molecule
that shows potential for inducing biofilm dispersal. Its life cycle involves a
planktonic stage, a fixed stage, and a stage in which groups of cells detach
from the biofilm surface. It is the molecule cis-2-decenoic acid released
during the final stage that is potentially responsible. This could be applied
to surfaces in the marine environment when the biofilm is unwanted.
Davies and Marques (2009)
tested the effect of several potential dispersal inducers produced by P. aeruginosa PAO1on biofilm dispersal
and inhibition of the same strain, and on biofilm dispersal of 6 bacterial
isolates and 1 fungal isolate, which all occur within marine environments. A
random assortment of air-born microbes was also investigated.
Potential
dispersal inducers were isolated from P.
aeruginosa PAO1 cultures grown continuously over 7 days: spent medium (SM),
all organic compounds found in SM, purified with a chloroform extraction (CSM),
and several individual compounds from CSM. A combination of centrifugation,
filtration, chloroform extraction and high-performance liquid chromatography
were used, depending on the isolate. Several concentrations were tested.
Continuous
cultures of P. aeruginosa PAO1 were
grown in flow cells for 4 days prior to treatment. Biofilm dispersal and
inhibition were assessed by observing the surface of the flow cells through an
attached microscope, and determining the cell densities of dispersed cells using
a spectrophotometer on spent medium collected throughout time points of the
trial. SM induced some dispersal, CSM induced complete dispersal after 30
minutes and cis-2-decenoic acid, isolated from the CSM, induced the same amount
of dispersal as CSM. Dispersal began from the outside of colonies as opposed to
the middle, contrary to natural dispersions which begin in the middle and form voids. CSM also
inhibited biofilm formation of P.
aeruginosa PAO1.
Similar
techniques used on the species Escherichia
coli; Klebsiella pneumonia; Proteus mirabilis; Streptococcus pyogenes;
Bascillus subtilis; Staphylococcus aureus and Candida albicans, cultured in microtiter plate wells, found only
CSM (containing cis-2-decenoic acid) induced dispersal. Concentrations equal to
that in natural biofilms (2.5 nM) caused these effects. Various
levels of pH, temperature and medium salt, and filtered spent medium, induced
no dispersal, supporting the theory of cis-2-decenoic acid being responsible
for all strains tested.
All
microbes were grown in the same conditions in terms of temperature (room) and
medium (modified EPRI), which may not be optimum for each strain, however this
is more representative of natural conditions in that all organisms would
experience the same external conditions.
A
benefit of using molecules from a strain of P.
aeruginosa is the ease of culturing it under laboratory conditions. A
molecule is applied as opposed to attempting to apply organisms directly,
removing the chance of unwanted side effects. Applying this molecule to
biofilms on surfaces in marine environments may be hard considering dispersal
of the molecule in the water. However the application is successful when the
medium is flowing, therefore the molecule may not need to linger for long to
induce dispersal.
The
compound cis-2-decenoic acid disperses biofilms of all bacteria species stated,
as well as the fungus. This is likely to translate to further species considering
the wide range of species affected. Potentially biofilm formation can be
inhibited, although this was only confirmed for P. aeruginosa. The application on surfaces in the marine
environment needs more research to perfect the application.
Davies, D. and Marques, C. (2009) A Fatty Acid Messenger Is Responsible for Inducing
Dispersion in Microbial Biofilms J Bacteriol. 191(5): 1393–1403
Megan
Hi Meg,
ReplyDeleteThis is a interesting post! If a method could be found and applied to the environment it would be great as an alternative to toxic antifoulants. I was just wondering if the authors mention much about the mechanism by which the dispersal of the biofilm is achieved?
Thanks, Georgia
Hi Georgia,
ReplyDeleteThe researchers did not state the specific mechanisms as such for any strain investigated. One of my ideas was that the removal of oxygen from the biofilm could induce dispersal considering cis-2-decenoic is an unsaturated fatty acid, and oxygen depletion has been linked with biofilm dispersal. Some of the other isolated compounds from CSM were mono-unsaturated fatty acids, which provided no dispersal so this is unlikely the cause. Also this would surely result in aggregates breaking down as opposed to intact clusters of cells remaining in the samples, as is observed here.
They stated the most likely reason for dispersal of P. aeruginosa is the molecule acting as a vector for cell-to-cell communication that stimulates the detachment of cells from the substratum but not each other. One of the impacts induced by this in other species is altered gene regulation: phenotypical changes have been observed such as filamentation. These changes prepare the cells for the detached phase, in this example the filaments could benefit the cells by allowing the control of movement.
The mechanism may be similar for the other strains of bacteria and the fungus that do not naturally have detachment phase of their lifecycle, however they were once planktonic. This molecule could induce changes that revert the cells back to their a state similar to their original, however this does not explain why the cells maintain clusters.
The detachment at low levels supports this idea of cell-to-cell communication for all strains investigated, even though there are still questions about the specific mechanisms.
I hope this helps!
Megan