Although occurring less, oil spills have huge environmental impacts. Several
different techniques have been used to removal oil from marine ecosystems, one
with potential is bioremediation. Previous work in this areas has focused
largely on Bacteria and those who have looked into the use of fungi have not,
as yet, demonstrated if fungi isolated from contaminated sites, can use crude
oil as their sole carbon source. Bovio et al (2017) made use of a spill off the
coast of Sicily, in 2013 to help provide some insight into this question as
well as investigating the mycobiota post disaster.
Three days after the spill, seawater and sediment was collected and
marine fungi were cultured. The numbers of Colony Forming Units were estimated and
fungi were identified. A fluorochrome was used to evaluate if fungi were
actively growing. Actively growing colonies were isolated and exposed to crude
oil within the medium and the percentage of stimulation was calculated. Four strains
that grew the best with crude oil were assessed for the ability to use oil as
their sole carbon source.
Nearly all of the taxa identified in the water column and sediment were
Ascomycota (94%), this was in accordance with previous research. But, a lower
biodiversity was observed within the sediment. Several unrecorded species were present,
12 species in the water column and 14 in the sediment. All 142 fungi
isolated could grow on crude oil but differed in efficiencies; not all were
positively affected, 27% (water column) and 33% (sediment) were inhibited. For
the four strains that responded positively to crude oil (Aspergillus terreus MUT 271; Lulworthiales sp. MUT 263; Penicillium citreonigrum MUT 267 75; Trichoderma harzianum MUT 290), biomass
was higher in the presence of crude oil. These strains also showed moderate
ability to remove petroleum hydrocarbons, greater than n-C30. Other species within these genera have been attributed to oil
degradation previously.
I think this is a good paper, helping to
add to the promising field of bioremediation, with possible oil degrading strains
of fungi for future research. One element of this paper which is of concern to me
is how quickly the sample was taken after the oil spill. Although focusing on
another domain of life, Kimes et al (2014) found that Obligate
hydrocarbonoclastic bacteria took a little while to increase in abundance.
Although increases occurred shortly after, this did not represent a long term
oil affected community. Despite this, I think it is also important to know how
the fungal community is affected short term too. Therefore I think it would be
interesting to resample this previously unstudied system to gain a better
understanding of how this dynamic system changes with a major damaging
environmental change, such as an oil spill.
Hi Chlobro123456789
ReplyDeleteCongratulations on finding such a newly published paper! I think this is a really great paper, and you've really nicely summarised the key points. I agree with you in regard to the time scale, and if the experiment was continued for longer it would be interesting to see whether the same fungal species maintained their positive or negative growths; 3 days really isn't long enough to determine any real relationship. It's also interesting that the majority of diversity was found within the water column, as most fungal diversity is within sediment. It would be interesting to see whether the diversity in the sediment increased over time.
Thank you!
Harriet
Chlobro123456789,
ReplyDeleteThank you for your review of this paper. Harriet congratulates you above for 'finding such a newly published paper', however, Tabitha Figgins already reviewed this paper last year (http://2015-mbio322.blogspot.co.uk/2016/11/marine-fungi-as-bioremediators.html). I would like to know what your thoughts on her previously stated criticism are and why you agree/disagree with her?
Thank you
Scott
Chlobro123456789,
ReplyDeleteFollowing on from my previous response. Both you and the authors talk of marine fungi using crude oil as their sole carbon source. As you may know crude oil is a complex mix of hydrocarbons, organic compounds containing oxygen, nitrogen and sulfur, trace amounts of various metals such as iron, nickel and copper and many other compounds. I have attached a reference below with some more information on the composition of crude oil if you're interested (Westlake et al., 1974). As such I have a few questions:
1) I was wondering what your opinion is on the author using crude oil as a sole carbon source?
2) Do you perhaps think there would be a better method to study degradation of crude oil by separating out the carbon based components and testing them as pure individual carbon sources or do you think the addition of the other components makes it for a more realistic experiment as naturally marine fungi would not degrade pure hydrocarbons like that?
3) As all crude oil is different do you think that by chance if this experiment was done again on a different sample of oil collected elsewhere that the results would be drastically different? Do you think that the 'four strains which grew the best' would differ? This being due to a different ratio and presence of carbon based compounds in the oil being more or less usable by these species of marine fungi.
You mention that 'those who have looked into the use of fungi have not, as yet, demonstrated if fungi isolated from contaminated sites, can use crude oil as their sole carbon source'. I was wondering if you had seen the paper by Kirk and Gordon on hydrocarbon degradation and what your opinion on it is (Kirk and Gordon, 1988)? Whilst it does not focus on oil spills directly it does look closely at the ability of marine fungi to degrade hydrocarbons in oil polluted and non polluted sites. The authors also look at a specific hydrocarbons found in crude oil, hexadecane.
I look forward to your response.
Cheers,
Scott
Kirk, P. and Gordon, A. (1988). Hydrocarbon Degradation by Filamentous Marine Higher Fungi. Mycologia, 80(6), p.776.
Westlake, D., Jobson, A., Phillippe, R. and Cook, F. (1974). Biodegradability and crude oil composition. Canadian Journal of Microbiology, 20(7), pp.915-928.
Hi,
DeleteI agree with Tabby on everything she said. The authors do not consider the SML and they could have a very important role in bioremediation.
In answer to your questions:
1) I am uncertain as to how realistic it is than an organism would use only carbon. But I do not know enough about the biology of these organisms to make a fully informed decision.
2)I think both methods could be viable. Knowing individual compounds that fungi (and other oil degraders, such as OHCB) could be useful to know the perfect and optimal mix of organisms for bioremediation. But I also think knowing how it works as a whole is also essential as individual components may not have the same effect as crude oil as a pollutant.
3)A different sample of oil may well have a similar affect, as the authors suggest in the paper these are commonly attributed to oil degradation or being able to degrade complex molecules. But with such little work in this area, I feel it is difficult to know whether this community would be the same with a slightly different composition.
As for elsewhere, this experiment was carried out on samples taken in the Mediterranean. With warmer average temperatures than some areas in North Pacific and Atlantic, it is possible that assemblages are different, if samples were taken from these locations. Although they may still have the same core ones, e.g Aspergillus spp. and Penicillium spp.
The Kirk and Gordon (1988) paper was cited by Bovio et al, but I have not read this paper and cannot get access to read it fully. But the authors use it to support Lulworthiales being able to degrade various grades of oil, including crude oil.
Thanks,
Chloe
Chloe,
ReplyDeleteThank you for your response. It appears there may be some confusion about my first question. I was wondering your opinion on the author using crude oil as a sole carbon source when it isn't a pure source of carbon. Crude oil is so varied in its composition and contains many other organic and inorganic compounds. These other varying compounds surely flaw the methods as they're not being controlled for?
Cheers,
Scott
Hi Scott,
DeleteI think the authors use crude oil, rather than specific constituents, since they are looking at how effective different fungi are at using it as a carbon source - with the intention of assessing their suitability as bioremediators, i.e. how well they could clean up a crude oil spill.
Looking at their ability to utilise specific hydrocarbons may be useful, but using crude oil as a whole is a more realistic experimental scenario for this particular study's aims.
Hope this answers your query, Tabby
Also, I forgot to mention, the authors do look at which apliphatic hydrocarbons are depleted after 10 days of incubation (of the pure fungal cultures with crude oil). This removes the need for them to look at each group of hydrocarbons separately.
DeleteThanks, Tabby
Tabby,
DeleteThank you for your response. I understand that the authors have chosen to use crude oil so they can assess how easy it would be to remove it from the environment. My point is that crude oil is complex, so differs in every case. So they are assessing the ability to degrade this batch of crude oil only. If they looked at specific hydrocarbons which are broken down, then they will know which exact compounds are being removed from the environment if fungi were used in future spills. This would allow them in future studies to look for other ways to remove the remaining constituents. I see from your second comment that they do indeed do this. I must have missed this from my read of the paper.
My other point is that they use it as a sole carbon source, but it isn't just a carbon source. How can we know that it isn't one of the metal compounds present in that batch of oil which is allowing the fungi to break down the hydrocarbons or the nitrogen compounds. Next time there is a spill, that compound might not be in as large a concentration and the ability of the fungi to break down the crude oil could be hindered.
Cheers,
Scott
Hi Scott,
DeleteI understand your point, because oil from different geographic regions does vary drastically in its composition. Knowing what sized hydrocarbons different microbial groups can degrade will be useful regardless of the type of oil, since the oil will likely contain similar constituents just in different amounts depending on it's origin.
Also, the results from this study seem to show that one species can degrade many hydrocarbons within a certain size range (see Table 5 in Bovio et al 2017), so repeating this study with every variation of crude oil available would be unnecessary and would probably not yield any surprising results that cannot be determined from studies such as this one.
Also, metals make up less than 0.01% of crude oil, and the metals aren't necessarily the most concerning constituent of crude oil.
Thanks, Tabby
Tabby,
DeleteUnfortunately I have to disagree. Crude oil's constituents will vary on their origin as different areas of the world have different mineral in the rocks. I am not suggesting that the study is repeated with each type of crude oil. I think the study would be better if the authors had used pure hydrocarbons instead of oil. I agree with you that metals make up very little of the oil, it was an extreme example I have to admit.
Thank you for your response,
Scott