067). The total abundance of viruses determined by means of electron microscopy ranged

from 1.91×107 ml−1 to 5.06×107 ml−1 without significant differences (p = 0.15; df 11) between the freshwater and saline zones of the lagoon. In terms of abundance, Myoviridae were dominant at all the study sites ( Table 1), and the numerical distribution of this family as well as of Podoviridae and non-tailed phages between the freshwater and saline parts of the lagoon was insignificant (p > 0.05; df 11). However, the distribution of Siphoviridae did differ significantly (p = 0.002; df 11) between the northern and central parts of the lagoon. The minimum (45.70 μg l−1) chlorophyll a concentration was recorded in the saline part of the lagoon, the maximum (186.60 μg l−1) in its freshwater part. The differences Y-27632 chemical structure (p > 0.05) between these zones were random LY294002 supplier and did not correlate with the total number of viruses, but were positively

correlated (r = 0.89; p < 0.001) with the abundance of Myoviridae. The total bacterial abundance varied between 0.64×106 ml−1 and 1.66×106 ml−1 and did not differ between fresh and saline waters either. The virus to bacteria ratio (VBR) varied from 15.6 to 49 at different stations, without a significant increase in the freshwater part of the Curonian Lagoon. However, VBR was negatively correlated with the total number of bacteria (r = –0.60; p < 0.05). It should be noted that only Podoviridae were positively correlated (r = 0.57; p = 0.052) with VBR, whereas the total number of phages were not correlated with VBR or the total abundance of bacteria. Twenty-six different phages from the Curonian Lagoon are described on the basis of morphological properties. The importance of this phenotypic diversity is of interest not only within a particular aquatic environment or at a particular time but could be useful in considerations of annual shifts of interactions between phages

and their hosts and for comparisons between similar environments. There are still no data ever on the diversity of phage-like particles from other Baltic Sea lagoons. However, the morphology of the members of the Podoviridae found in the Curonian Lagoon was similar to that observed by Wichels et al. (1998) and less diverse than the morphology of the members of the Myoviridae and Siphoviridae. Most of the phages possessed tails, which suggests that they are not viruses of eukaryotes. However, tailless phage-like particles ca 200 nm in size were found very occasionally at three different sites (1, 8 and 11; Figure 2aa). Sommaruga et al. (1995) described similar phage-like particles with sizes between 195 and 210 nm from a eutrophic water body, suggesting an association between the occurrence of these particles and anthropogenic impact. In our case it was hard to define the occurrence of these large phage-like particles owing to their low frequency of occurrence and distribution throughout the study area.