Ethanol-preserved Tissue Research Articles

Recovering the genomes hidden in museum wet collections.

Natural history museums hold vast collections of biomaterials. The collections in museums, often painstakingly sampled, are largely unexplored treasures that may help us better understand biodiversity on the planet. Museum collections can provide a unique window into the past of species long gone or currently declining due to human activity. From a molecular perspective, however, many museum samples are stored under conditions that hasten the damage of DNA, RNA and proteins. For example, samples in wet collections are those stored in liquid preservatives, typically ethanol. These ethanol-preserved tissues are often, although not always, formalin-fixed prior to storage, which may damage DNA. In this and recent issues of Molecular Ecology Resources, Straube et al (2021), O'Connell et al (2021) and Hahn et al (2022) explore different types of specimens from museum wet collections as new sources of DNA for scientific studies. All three articles found that for wet museum collections, overall specimen condition mattered most for recovering high-quality genomic DNA.

Decade-scale stability and change in a marine bivalve microbiome.

Predicting how populations and communities of organisms will respond to anthropogenic change is of paramount concern in ecology today. For communities of microorganisms, however, these predictions remain challenging, primarily due to data limitations. Information about long-term dynamics of host-associated microbial communities, in particular, is lacking. In this study, we use well-preserved and freshly collected samples of soft tissue from a marine bivalve host, Donax gouldii, at a single site to quantify the diversity and composition of its microbiome over a decadal timescale. Site-level measurements of temperature, salinity and chlorophyll a allowed us to test how the microbiome of this species responded to two natural experiments: a seasonal increase in temperature and a phytoplankton bloom. Our results show that ethanol-preserved tissue can provide high-resolution information about temporal trends in compositions of host-associated microbial communities. Specifically, we found that the richness of amplicon sequence variants (ASVs) associated with D.gouldii did not change significantly over time despite increases in water temperature (+1.6°C due to seasonal change) and chlorophyll a concentration (more than ninefold). The phylogenetic composition of the communities, on the other hand, varied significantly between all collection years, with only six ASVs persisting over our sampling period. Overall, these results suggest that the diversity of microbial taxa associated with D.gouldii has remained stable over time and in response to seasonal environmental change over the course of more than a decade, but such stability is underlain by substantial turnover in the composition of the microbiome.

Enzymatic detection of formalin-fixed museum specimens for DNA analysis and enzymatic maceration of formalin-fixed specimens

Abstract A simple enzymatic screening method has been developed to detect whether a tissue sample has been preserved with formalin or with ethanol only because such a method is a useful tool for predicting the quality of genetic test results. The method is based on enzymatic digestion at 55°C at neutral pH. The screening method shows that only ethanol-preserved tissue samples are dissolved, whereas formalin-preserved samples remain undissolved. The method was developed by the incorporation of laboratory rats preserved under controlled conditions in either 4% neutral buffered formalin or 96% ethanol. The method was subsequently tested on wild-living preserved specimens and an archived specimen. The protease enzyme used was Savinase® 16 L, Type EX from Novozymes A/S. The enzymatic screening test demands only simple laboratory equipment. The method is useful for natural history collections in museums where DNA analyses of archived specimens are performed. Wasted time and resources can be avoided through the detection of formalin-fixed specimens because these specimens yield low-quality, damaged DNA. In addition to the screening method, it is shown that formalin-preserved specimens can be macerated by enzymatic digestion under alkaline conditions at 55°C.

DNA and Mini-DNA barcoding for the identification of Porgies species (family Sparidae) of commercial interest on the international market

The morphological similarity among Sparidae species, which are characterized by a different market price, represents a serious problem for their trade and for stock management, since it encourages frauds for substitution. The most accredited morphological method for their identification is based on the dental-plate, but this approach is not simple and cannot be used for prepared products. When molecular methods are used the DNA degradation induced by cooking is the main drawback. In this work, we collected 314 reference tissues belonging to 75 Sparidae species and we produced a dataset of full (FDB) and mini-barcode (MDB) reference sequences starting from DNA extracted from fresh and ethanol-preserved tissues using universal primes. Moreover, some fresh samples were cooked. The FDB was successfully amplified in 91% (fresh), 50% (cooked) and 81% (ethanol-preserved) samples, while the amplification rates of the MDB were considerably higher in case of cooked (100%) and ethanol-preserved (94%) samples. The same primers were used for the amplification of the DNA obtained from 58 market samples (MS). All the DNA barcodes were compared with BOLD and GenBank using IDs and BLAST analysis. FDB was able to provide unambiguous species-level identifications for 53 (78%) and 44 (64.7%) reference samples analyzed on BOLD and GenBank, respectively. The Mini-DNA barcode (MDB) showed a lower discriminating power with 32 (45.7%) and 29 (41.4%) sequences unambiguously matched to a species on BOLD and GenBank. However, the MDB allowed to identify all the reference sequences as belonging to the Sparidae family. FDB and MDB showed a similar performance in analyzing the MS, allowing to highlight 21 (38%) mislabeled MS. Our study, while confirming the FDB as a reliable tool for fish authentication, proposes the MDB as a promising tool to recover molecular information in case of cooked products.

Genome size estimates for crustaceans using Feulgen image analysis densitometry of ethanol-preserved tissues.

Crustaceans are enormously diverse both phylogenetically and ecologically, but they remain substantially underrepresented in the existing genome size database. An expansion of this dataset could be facilitated if it were possible to obtain genome size estimates from ethanol-preserved specimens. In this study, two tests were performed in order to assess the reliability of genome size data generated using preserved material. First, the results of estimates based on flash-frozen versus ethanol-preserved material were compared across 37 species of crustaceans that differ widely in genome size. Second, a comparison was made of specimens from a single species that had been stored in ethanol for 1-14 years. In both cases, the use of gill tissue in Feulgen image analysis densitometry proved to be a very viable approach. This finding is of direct relevance to both new studies of field-collected crustaceans as well as potential studies based on existing collections.

The complete mitochondrial genome of a turbinid vetigastropod from MiSeq Illumina sequencing of genomic DNA and steps towards a resolved gastropod phylogeny

A need to increase sampling of mitochondrial genomes for Vetigastropoda has been identified as an important step towards resolving relationships within the Gastropoda. We used shotgun sequencing of genomic DNA, using an Illumina MiSeq, to obtain the first mitochondrial genome for the vetigastropod family Turbinidae, doubling the number of genomes for the species-rich superfamily Trochoidea. This method avoids the necessity of finding suitable primers for long PCRs or primer-walking amplicons, resulting in a timely and cost-effective method for obtaining whole mitochondrial genomes from ethanol-preserved tissue samples. Bayesian analysis of amino acid variation for all available gastropod genomes including the new turbinid mtgenome produced a well resolved tree with high nodal support for most nodes. Major clades within Gastropoda were recovered with strong support, with the exception of Littorinimorpha, which was polyphyletic. We confirm here that mitogenomics is a useful tool for molluscan phylogenetics, especially when using powerful new models of amino acid evolution, but recognise that increased taxon sampling is still required to resolve existing differences between nuclear and mitochondrial gene trees.

Tissue sampling methods and standards for vertebrate genomics.

The recent rise in speed and efficiency of new sequencing technologies have facilitated high-throughput sequencing, assembly and analyses of genomes, advancing ongoing efforts to analyze genetic sequences across major vertebrate groups. Standardized procedures in acquiring high quality DNA and RNA and establishing cell lines from target species will facilitate these initiatives. We provide a legal and methodological guide according to four standards of acquiring and storing tissue for the Genome 10K Project and similar initiatives as follows: four-star (banked tissue/cell cultures, RNA from multiple types of tissue for transcriptomes, and sufficient flash-frozen tissue for 1 mg of DNA, all from a single individual); three-star (RNA as above and frozen tissue for 1 mg of DNA); two-star (frozen tissue for at least 700 μg of DNA); and one-star (ethanol-preserved tissue for 700 μg of DNA or less of mixed quality). At a minimum, all tissues collected for the Genome 10K and other genomic projects should consider each species’ natural history and follow institutional and legal requirements. Associated documentation should detail as much information as possible about provenance to ensure representative sampling and subsequent sequencing. Hopefully, the procedures outlined here will not only encourage success in the Genome 10K Project but also inspire the adaptation of standards by other genomic projects, including those involving other biota.

Population genetic structure of the salmon louse,Lepeophtheirus salmonis(Krøyer) on wild and farmed salmonids around the Pacific coast of Canada

The population genetic structure of the salmon louse (Lepeophtheirus salmonis: Caligidae) is of considerable interest because of indirect evidence suggesting transmission of this ectoparasite between wild salmon and farmed salmon (reviewed by Boxaspen 2006). Consequently several studies have looked for farm-speci¢c molecular markers that would allow the path of transmission to and from wild ¢sh to be traced. Unfortunately, an early report of RAPD markers that were speci¢c to Scottish salmon farms (Todd,Walker,Woli, Northcott,Walker, Ritchie, Hoskins, Abbott & Hazon 1997) was not found in a second RAPD study (Dixon, Shinn & Sommerville 2004) or in a more extensive study using six microsatellite markers (Todd, Walker, Ritchie, Graves & Walker 2004). Nevertheless, interest in ¢nding farmspeci¢c molecular markers continues. It is still not possible to follow the salmon lice larvae during the 4^14-day period they spend in the plankton before they infect a host (Johnson & Albright 1991). We therefore tested the research hypothesis that population genetic structure existed among salmon lice populations collected from diierent geographical regions of British Columbia, Canada, because of restricted gene £ow. Samples of the salmon louse, L. salmonis, were obtained from three diierent wild Paci¢c salmon species by sports ¢shing and during creel (sports ¢shery catch) surveys and from farmed Atlantic salmon by netting (Table 1). Sea lice were removed from each salmon host with forceps and preserved in 95% ethanol. To test for population genetic structure with the largest sample size possible, we decided to use a fragment of the mitochondrial cytochrome c oxidase subunit 1 (COI) (Folmer, Black, Hoeh, Lutz & Vrijenhoek1994) that has been extensively used for DNA barcoding (Hebert, Cywinska, Ball & deWaard 2003). This allowed us to make use of a large number of existing salmon louse COI sequences and to easily compare the sequence divergence that we observed among diierent clades with that of other species of animals (Hebert et al. 2003). Template DNA was extracted from individual salmon lice using modi¢ed proteinase K methods. A 1mm piece of ethanol-preserved tissue was obtained fromeach specimenand placed directly into 96-well plates containing lysis buier and proteinase K. Subsequent DNA extraction used a glass ¢bre protocol (Ivanova, deWaard & Hebert 2006). A 710-bp fragment of the COI genewas polymerase chain reaction (PCR) ampli¢ed using the primer pairs LCO1490 and HCO2198 (Folmer et al.1994) or LepF1and LepR1 (Hebert, Penton, Burns, Janzen & Hallwachs 2004) and visualized ina 96-well E-Gel (Invitrogen Canada, Burlington, ON, Canada). The PCR mix included 6.25 mL of 10% trehalose, 1.25 mL 10 PCR buier, 0.625 mL (50mM) MgCl2,0.125 mL (10 mm) of each primer, 0.0625 mL (10mM) dNTPs, 0.0625 mL Platinum Aquaculture Research, 2009, 40, 973^979 doi:10.1111/j.1365-2109.2008.02159.x

A simplified protocol for routine total DNA isolation from salmonid fishes

An efficient total DNA isolation protocol, suitable for routine population genetic screening purposes is described. This phenol based extraction can utilize fresh, frozen or ethanol preserved tissues.

Animal Colonies — Development and Function through Time

A need to increase sampling of mitochondrial genomes for Vetigastropoda has been identified as an important step towards resolving relationships within the Gastropoda. We used shotgun sequencing of genomic DNA, using an Illumina MiSeq, to obtain the first mitochondrial genome for the vetigastropod family Turbinidae, doubling the number of genomes for the species-rich superfamily Trochoidea. This method avoids the necessity of finding suitable primers for long PCRs or primer-walking amplicons, resulting in a timely and cost-effective method for obtaining whole mitochondrial genomes from ethanol-preserved tissue samples. Bayesian analysis of amino acid variation for all available gastropod genomes including the new turbinid mtgenome produced a well resolved tree with high nodal support for most nodes. Major clades within Gastropoda were recovered with strong support, with the exception of Littorinimorpha, which was polyphyletic. We confirm here that mitogenomics is a useful tool for molluscan phylogenetics, especially when using powerful new models of amino acid evolution, but recognise that increased taxon sampling is still required to resolve existing differences between nuclear and mitochondrial gene trees.