[Nhcoll-l] 95% vs. ~70% EtOH?

[Dirk Neumann]

Dear Sonia,

dehydration is not a caveat if you aim to preserve tissues for later / 
future DNA analysis - this is what you aim for, as residual water 
degrades the DNA helix. The long term preservation of DNA not only 
depends on the ethanol you use (for tissues storage use only undenatured 
pure ethanol and avoid technically dried alcohols above 96% for this 
purpose), but also on general storage settings. Tissues should be stored 
frozen, at least at -25°C, better would be -80°C, best option surely is 
liquid nitrogen - which is not feasible in many institutions / 
collections for various reasons however.

Dehydration and osmolarity surely is an issue for the preservation of 
the soft tissues and lead to cell rupture, which should be avoided in 
any case.

If your collections aims in both directions, keeping tissues fit for DNA 
analysis and voucher specimens for morphological comparison, I would 
advise indivdualised tissue subsamples in pure ethanol at -25/-80°C.

For normal collection storage, the ethanol concentration should not drop 
below 50%, as the water supports tissue degradation, especially in 
marine invertebrates. Specific marine invertebrates such as bryozoans 
might require special attention towards fixation / preservation of 
tissues, but I am not an expert in these groups. However, keep in mind 
that if you use highly concentrated denatured / undenatured ethanol for 
specimen storage, that you might trigger pH issues for long term 
storage, as carbonates might be dissolved out of the coral skeleton but 
pure ethanol has nearly zero buffering capacity. This might not be that 
much of an issue with coral specimens, but with other soft tissued 
invertebrates in your collection that receive the same treatment.

All the best
Dirk




Am 29.07.2014 10:31, schrieb Sonia Rowley:
> Dear List
>
> I am writing with regards any experience and evidence for and against 
> the use of 95% or ~70% EtOH for longterm invertebrate (specifically 
> gorgonian coral) specimen preservation for collections. More and more 
> institutions seem to be turning to 95% EtOH, however, there are 
> numerous conflicting thoughts and evidence with regards the use of 
> higher concentrations for longterm specimen storage. Furthermore, I 
> understand that there are 2 types of high EtOH concentration; clean 
> and dirty with the latter being far cheaper but unsuitable for genetic 
> analyses.
>
> Whilst collections are indeed a taxonomic concern, this does include 
> the use of molecular work as part of the suite of tools in determining 
> species differences. The collections I have worked in using ~95% EtOH 
> have had good success with both storage and genetic work, but these 
> specimens may often be a maximum of 1 - 2 decades old. Conversely, 
> others mention caveats such as the high concentration dehydrating the 
> specimen to such an extent that it disrupts the integrity of both 
> specimen and DNA. At the same time the often high water content of 
> specimens is said to bring down the EtOH concentration which may also 
> cause issues with specimen degradation.
>
> Please excuse the somewhat rudimentary nature of my question, there 
> does seem a tremendous amount of confliction in what is recommend and 
> therefore it would be really valuable to hear what people have to say 
> and recommend from the list.
>
> Thank you for your time with this matter and look forward to hearing 
> any responses
>
> Sonia
>
> -- 
> Sonia J. Rowley PhD
> Research Affiliate
> Bernice Pauahi Bishop Museum
> 1525 Bernice St, Honolulu,
> HI 96817,,USA
> +1 808 348 6224
>
> Research Affiliate
> University of Hawai'i at Manoa
> 2538 McCarthy Mall, Edmondson 312
> Honolulu, HI 96822
>
>
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-- 
Dirk Neumann

Tel: 089 / 8107-111
Fax: 089 / 8107-300
email: Dirk.Neumann(a)zsm.mwn.de

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---------

Dirk Neumann

Tel: +49-89-8107-111
Fax: +49-89-8107-300
email: Dirk.Neumann(a)zsm.mwn.de

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