Fungi are a monophyletic group that has
been found across all parts of the world. These fungi are very diverse, some
being filamentous and containing structures known as hyphae, whilst other fungi
are single celled with no hyphae. Many of these filamentous fungi produce
hydrophobins - small proteins of about 100 amino acids that are the most
powerful surface-active proteins to our current knowledge. Hydrophobins have an
amphiphilic structure, with their hydrophobic aliphatic side chains able to
create a coating on the surface of an object. These properties have been shown
to have uses in coating of spores, which allows the fungus to move about and to
attach to different surfaces.
Cicatiello et al (2016) aimed to identify
marine fungi as a source of hydrophobins. Hydrophobins were split into Class I
and Class II, depending on their properties. Class I form highly stable, highly
insoluble aggregates and have distinct rodlets, whereas Class II are less
stable and lack the ability to form rodlets.
Marine fungi was isolated from the seagrass
Posidonia oceanica, the green alga Flabellia petiolata and the brown alga Padina pavonica near Elba island in the
Mediterranean sea. Each marine fungal strain was maintained on an agar plate at
20OC. To extract Class I and Class II hydrophobins from the culture
broth, proteins were aggregated by bubbling air using a Waring blend, and the
foam was collected and treated with 20% trichloroacetic acid.
To extract Class II hydrophobins from the
mycelium, mycelia were washed with water and proteins were extracted using 60%
ethanol in a bath sonicator. Class I hydrophobins were extracted using 2%
sodium dodecyl sulphate, water, 60% ethanol and trifluoroacetic acid.
The results showed that 23 out of the 100
strains of marine fungi were chosen due to their foam producing capabilities in
shaken cultures, thus showing the production of biosurfactants. The isolation
of Class I and Class II hydrophobins from the culture broth and the mycelium
allowed the identification of 6 new putative hydrophobins that could be used in
biotechnological instances in the future.
This study provided evidence for marine
fungi as sources of hydrophobins, and seemed to go beyond the aims they set by
trying to look at the functions of the identified hydrophobins. Whilst this is
a good thing, it did seem to get confusing at times as to what they were trying
to achieve. The way it was written was also confusing at times as the parts of
the methods seemed to appear in the results and discussion sections. This paper
could be more clear and concise on just what it was trying to show, and could
be written better, but I think the overall conclusion and results seemed to
show that the study was successful in reaching its aim.
Reviewed paper: Cicatiello, Paola.,
Gravagnuolo, Alfredo. Maria., Gnavi, Giorgio., Varese, Giovanna. Cristina., and
Giardina, Paola. (2016). Marine fungi as a source of new hydrophobins.
International journal of biological macromolecules. 92: 1229-1233. http://www.sciencedirect.com/science/article/pii/S0141813016311928
Hi Amy,
ReplyDeleteGreat post, you mentioned that the authors aimed to look at the function of the hydrophobins, did they conclusively determine any of the functions?
Do you think that the marine fungal hydrophobins seen in this study are widespread in marine fungi as they are in terrestrial species?
Thanks
Natasha
Hi Natasha,
ReplyDeleteThank you for your questions. They showed the ability for the putative hydrophobins to self-assemble into a stable amphiphilic layer, and to functionalize a solid surface. This helped them to determine which hydrophobins were in Class I and in Class II. The emulsification capacity was also tested in the 6 new putative hydrophobins, and all 6 were able to produce oil/water emulsions.
I think that it is highly possible that these hydrophobins are widespread in marine fungi, as being able to create surfactants seems to be incredibly useful, especially in the marine environment where the fungi needs to move through the liquid medium.
I hope this answers your questions.
Thanks,
Amy
Hi Amy,
ReplyDeleteLove this sort of paper, looking into possible biotechnological uses. I was wondering though, is the Class I and Class II system universal or just used by the authors?
Along with possible biotech uses, could these Hydrophobins be possible used for bioremediation purposes as I have seen it mentioned that many biosurfactants also enhanced emulsification with biodegradation potential of hydrocarbon pollutants.
Yadav, A., Manna, S., Pandiyan, K., Singh, A., Kumar, M., Chakdar, H., Kashyap, P. and Srivastava, A. (2016). Isolation and characterization of biosurfactant producing Bacillus sp. from diesel fuel-contaminated site. Microbiology, 85(1), pp.56-62.
Hi Stefan,
DeleteThank you for your question. It looks to me as though this system is universal as it seems to be mentioned in other papers (e.g. Askolin et al, 2006).
You've raised an interesting point that I hadn't actually considered. In a paper by Hobley et al, 2013, it's shown that biofilms have critical roles in bioremediation, and assembles with the help of a small secreted protein known as BslA. BslA is a structurally defined hydrophobin, so I suppose you could say that hydrophobins are used in bioremediation as this is evidence, and I expect there will be more evidence if there isn't already.
I hope this answers your question.
Thanks,
Amy
Askolin, S., Linder, M., Scholtmeijer, K., Tenkanen, M., Penttila, M., de Vocht, M. L., and Wosten, H. A. (2006). Interaction and comparison of a class I hydrophobin from Schizophyllum commune and class II hydrophobins from Trichoderma reesei. Biomacromolecules. 7(4): 1295-1301. https://www.ncbi.nlm.nih.gov/pubmed/16602752
Hobley, L., Ostrowski, A., Rao, F. V., Bromley, K. M., Porter, M., Prescott, A. R., MacPhee, C. E., van Aalten, D. M. F. and Stanley-Wall, N. R. (2013). BslA is a self-assembling bacterial hydrophobin that coats the Bacillus subtilis biofilm. PNAS. 110(33): 13600-13605. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3746881/