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Virus concentrations, virus-to-bacterium ratios ( VBRs) and levels of lysogenic phage were measured throughout the 110-m water column of epishelf Beaver Lake during the austral summer of 2003/2004. The aim was to determine which factor(s) controlled viral dynamics using detailed concomitant published data on inorganic nutrients, chlorophyll a, dissolved organic carbon ( DOC) and bacterial production for Beaver Lake ( Freshwater Biology, 51, 2006, 1119). Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the bacterial community was also undertaken to investigate the potential relationship between bacterial community composition and viral dynamics., Virus concentration ranged between 1.43 × 104 and 302.4 × 104 viruses mL−1 and showed a clear increase over the summer, while bacterial concentrations exhibited no seasonal pattern (range: 9.6 × 104 to 44.6 × 104 cells mL−1). Consequently, VBR varied with highest values in January (3.32-7.33)., The percentage of lysogenic phage was low, ranging from 0 to 11.69%, suggesting that other life cycles (i.e. lytic or possibly pseudolysogeny) were taking place. Attempts to measure viral production using both the Td R incorporation technique and the dilution technique failed to produce consistent results, in common with other ultra-oligotrophic Antarctic lakes., There were significant correlations between viral concentration and each of chlorophyll a, DOC, ammonium and nitrate concentrations and bacterial production, but not between bacterial abundance and either soluble reactive phosphorus or temperature., Lack of change in the dominant bacterial community composition over summer suggests that changes in viral concentrations were a function of changes in other biological and physicochemical factors, rather than changes in host/phage infection., The results suggest a significant connection between viruses and bacteria, with the DOC pool acting as a conduit for the movement of carbon between the two components. [ABSTRACT FROM AUTHOR]

There is now compelling evidence that microbially mediated reactions impart a significant effect upon the dynamics, composition, and abundance of nutrients in glacial melt water. Consequently, we must now consider ice masses as ecosystem habitats in their own right and address their diversity, functional potential, and activity as part of alpine and polar environments. Although such research is already underway, its fragmentary nature provides little basis for developing modern concepts of glacier ecology. This paper therefore provides a much-needed framework for development by reviewing the physical, biogeochemical, and microbiological characteristics of microbial habitats that have been identified within glaciers and ice sheets. Two key glacial ecosystems emerge, one inhabiting the glacier surface (the supraglacial ecosystem) and one at the ice-bed interface (the subglacial ecosystem). The supraglacial ecosystem is characterized by a diverse consortium of microbes (usually bacteria, algae, phytoflagellates, fungi, viruses and occasional rotifers, tardigrades, and diatoms) within the snowpack, supraglacial streams, and melt pools (cryoconite holes). The subglacial system is dominated by aerobic/anaerobic bacteria and most probably viruses in basal ice/till mixtures and subglacial lakes. A third, so-called englacial ecosystem is also described, but it is demonstrated that conditions within glacier ice are sufficient to make metabolic activity and its impact upon nutrient dynamics negligible at the glacier scale. Consideration of the surface and internal heat balances of the glacier show that all glacial ecosystems are sensitive to climate change, although at different timescales. Thus, while rapid, melt-driven habitat changes lead to melt-out, resuscitation, and redistribution of microorganisms in many supraglacial ecosystems, much slower climatic and glacial mass-balance processes effect such changes in the subglacial ecosystem. Paradoxically, it is shown that these forces have brought about net refreezing and the onset of cryostasis in the subglacial ecosystems of many Arctic glaciers subject to thinning in recent decades. [ABSTRACT FROM AUTHOR]

We examined the response of bacteria and proto- and metazooplankton to photomodified dissolved organic matter (DOM). Sterile filtered water from a eutrophic and a humic lake, that was either exposed to artificial ultraviolet (UV) radiation or kept dark, was added to semicontinuous laboratory microcosms that lasted for 7 weeks. Bacterial production responded positively to photochemical modification of DOM regardless of lake type. Final heterotrophic biomass (bacteria + proto + metazooplankton) was 47 ± 5 and 37 ± 5 µg carbon (C) L-1 in microcosms with UV-exposed and unaltered eutrophic water DOM and 15 ± 4 and 11 ± 2 µg C L-1 in microcosms with UV-exposed and unaltered humic water DOM, respectively. For the eutrophic water, there were no significant differences in proto- or metazooplankton biomasses between microcosms receiving UV-exposed or nonexposed DOM. Differences between eutrophic water microcosms were not significant when flagellates, ciliates, cladocerans, and copepods were examined separately. In microcosms with UV-exposed humic water, biomasses of heterotrophic flagellates, rotifers, nauplii, and cladocerans were higher than in those with nonexposed DOM. Higher final metazooplankton biomass following addition of UV-exposed humic water indicates that photochemically modified DOM can be effectively transferred through the microbial loop. [ABSTRACT FROM AUTHOR]