Evaluation of preservation methods for veliger detection field samples
A variety of different methods are currently in use for preservation of dreissenid mussel detection field samples.
Previous research has demonstrated that proper preservation of these samples is critical for subsequent detection of
both veliger shells by microscopy and mussel-specific DNA by polymerase chain reaction (PCR). The US Bureau of
Reclamation's (USBR) mussel detection laboratory in Denver, CO recommends the usage of isopropyl alcohol
(isopropanol/rubbing alcohol) and baking soda (sodium bicarbonate) for preservation of field collected water samples.
Isopropyl alcohol provides preservation of tissues and DNA, allowing for detection by PCR. Baking soda buffers
against acidification of the sample, thereby preserving the calcareous shells of veligers and allowing detection by
cross polarized light microscopy (CPLM). Isopropyl alcohol and baking soda where selected as the preservatives of
choice because they are inexpensive and readily obtained even in remote sampling locations.
A study by the Western Regional Panel subcommittee on mussel field sampling methods has evidenced that other
laboratories vary in the preservation methods they request for field samples. For alcohol preservation, some
laboratories request the use of absolute or reagent grade ethyl alcohol (ethanol). This choice is based on the general
belief that ethyl alcohol is a superior preservative of DNA integrity, as compared to isopropyl alcohol. However,
research on this topic is scant and studies of other tissue types have suggested that isopropyl alcohol and ethyl
alcohol may be equally effective for short term preservation. There is also concern that rubbing alcohol obtained from
retail stores may contain additives which could inhibit extraction and recovery of DNA from samples. With regards to
practicality for field sampling, while absolute or reagent grade ethyl alcohol is frequently used for sample preservation
in research laboratories, it is significantly more expensive
Need and Benefit
Invasive dreissenid mussels represent a significant risk to USBR operations, having the potential to interrupt both
water conveyance and hydroelectric power generation.
USBR has a robust long-term sampling program for early detection of mussels across the western United States.
Multiple different preservation methods are currently in use by different laboratories, and the relative benefits and
shortfalls of these methods have yet to be evaluated in a rigorous and comparative manner.
USBR managers and other stakeholders are uncertain as to why multiple methods are in use for sample
preservation, how they compare to one another, and how the choice of preservation method may impact the results of
mussel early detection analyses.
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