Trinucleotide microsatellite loci for the zebra mussel Dreissena polymorpha,an invasive species in Europe and North America

The high mutation rate at microsatellite loci can supply important demographic information on founder events and range expansion in an invasive species such as the zebra mussel Dreissena polymorpha, following its initial introduction. In order to facilitate studies into the colonization patterns of this species in new habitats in Europe and North America, five trinucleotide microsatellite loci were isolated from a partial DNA library. Allelic diversity at all described loci was high, ranging from 20 to 35 alleles per locus. Homologous loci were not amplified in a second related invasive species, Dreisenna bugensis, using the primers developed here.     

Specific amplification of the 18S rRNA gene as a method to detect zebra mussel (Dreissena polymorpha) larvae in plankton samples

An important issue in the management of zebra mussel (Dreissena polymorpha) populations is early, rapid, and accurate detection of the planktonic larvae (veliger) of the zebra mussel. The goal of this study was to explore the feasibility of developing a molecular approach for the detection of zebra mussel larvae in diverse environments. In this study a Dreissena polymorpha-specific 18S ribosomal RNA gene targeted oligonucleotide primer (ZEB-715a) and Polymerase Chain Reaction (PCR) assay was developed and compared with cross-polarized microscopy as a means to detect zebra mussel veligers in plankton samples. The design of the zebra mussel-specific primer was facilitated by sequencing nearly the complete 18S rRNA gene from the zebra mussel and three other closely related freshwater Veneroids including the quagga mussel (D. bugensis), the dark false mussel (Mytilopsis leucophaeata), and the Asian freshwater clam (Corbicula fluminea). The specificity of the primer for the zebra mussel was empirically tested by using the primer as a direct probe in a blot hybridization format. A single veliger in a plankton sample could be detected by PCR using this approach. Veliger detection sensitivity using the PCR approach was estimated to be over 300 times more sensitive than cross-polarized light microscopy based techniques. Cross-polarized light microscopy and the PCR technique were used to identify the presence of zebra mussel larvae in plankton samples that were collected from a variety of natural and industrial water sources. Detection results (presence or absence) were generally consistent between the two methods. Although additional studies will be required before routine application of molecular based veliger detection technology is available, a long-term goal of this work is the application of molecular technology to the development of a field device for the routine detection and quantification of zebra mussel veligers.     

Indigenous microflora and opportunistic pathogens of the freshwater zebra mussel, Dreissena polymorpha

Freshwater fouling invertebrate zebra mussels (Dreissena polymorpha) harbor a diverse population of microorganisms in the Great Lakes of North America. Among the indigenous microorganisms, selective species are opportunistic pathogens to zebra mussels. Pathogenicity to zebra mussels by opportunistic bacteria isolated from the mussels was investigated in this study. Among the more than 30 bacteria isolated from temperature-stressed mussels, Aeromonas media, A. veronii, A. salmonicida subsp. salmonicida, and Shewanella putrefaciens are virulent pathogens to juvenile zebra mussels. Inoculation of a bacterial concentration of A. media, A. salmonicida subsp. salmonicida and S. putrefaciens at 10⁷ cells per zebra mussel resulted in 100% mortality within 5 days, and only 64.9% for A. veronii. In contrast, mortality was less than 12.3% following inoculation of a sterile phosphate buffer solution as a control. In addition, mortality was dependent on the size of the pathogen population used in inoculation and the incubation temperature, indicating the close relationship between the bacterial population and subsequent death. On the mussel tissue, a dense microbial population was evident from the moribund mussels viewed with Scanning Electron Microscope (SEM). Opportunistic bacteria invaded and destroyed the D. polymorpha tissue after 7 days of incubation when the bacterial inoculation was larger than 10⁵ per zebra mussel. Our results suggest that mussels are reservoirs of opportunistic pathogenic microorganisms to aquatic organisms and humans and a better understanding of the microbial ecology of the mussels will provide insights to the possible health hazards from these microorganisms.     

Horizontal and Vertical Distribution of the Zebra Mussel (Dreissena polymorpha,Pallas) Larvae in the Modrac Reservoir,Bosnia and Herzegovina

In the Modrac Reservoir, loaded with coal separation suspended material, rapid development of the zebra mussel (Dreissena polymorpha) took place from at least 1987. It is probably the first distinguished “infection” for this part of Balkan Peninsula, caused by this organism. Horizontal and vertical distribution of this mussel, at 15 different reservoir profiles, had been investigated.