Viruses, bacteria and suspended particles in a backwater and main channel site of the Danube (Austria)

Abstract

A short overview of currently available studies on the ecology of viruses in running waters is provided. Additionally, a survey was conducted on the dynamics of both viruses and bacteria in an isolated floodplain segment of the Danube River and in the main channel near Vienna (Austria) during the hydrologically most dynamic phase (spring -summer). The study evaluates the differences between the main channel and the floodplain segment for suspended particle abundance and quality in relation to bacterial and viral parameters; both free-living forms and those attached to particles are examined. The hydrological disconnection of these two contrasting sampling sites influenced particle abundance and quality as well as the distribution of free-living vs. attached bacteria and viruses. The per-cell activity of bacteria attached to particles was significantly higher than that of the free-living fraction, particularly in the isolated water body. The abundance of bacteria and viruses on particles depended on particle quality (size). In the main channel, bacteria were significantly more abundant on surfaces (per mm 2 ) of suspended matter > 5 μm (aggregates with organic constituents) compared to particles < 5 μm (mostly mineral grains). In the isolated water body, both bacteria and viruses were more abundant on the larger particles/ aggregates. Data from both locations revealed a positive correlation between abundance of particles > 5μm and attached viruses; free-living viruses were less abundant at high > 5μm particle loads. Only in the isolated floodplain section was viral abundance positively influenced by elevated per-cell productivity of potential host bacteria. The results demonstrate that system variability on a relatively small topographical scale (within a river-floodplain system) has consequences for microbial life, including viruses. KeywordsRiver-floodplain; seston; bacterial activity; virus ecology InroductionFollowing the discovery of high numbers of viruses in aquatic environments (now considered the most abundant biological entities in natural waters; Bergh et al., 1989), it soon was observed that this virioplankton is significantly linked to bacterio-and phytoplankton (Proctor and Fuhrman, 1990;Suttle et al., 1990). Since viruses infect all members of the microbial food web, they must be viewed as significant biological agents in microbial processes (for review see Wommack and Colwell, 2000;Weinbauer, 2004). Moreover, viral abundance is generally one to two orders of magnitude higher than that of bacterioplankton. Interestingly, there are indications that freshwater systems might differ from marine habitats regarding viral abundance and the ratio of viral to bacterial numbers (Maranger and Bird, 1995;Farnell-Jackson and Ward, 2003). Further surprising is that, although viruses play a significant role in marine and lake waters, many related aspects are largely ignored in research on the functioning of river systems.For many years the presence of viruses in river water has been a significant public ...

Deciphering the virus‐to‐prokaryote ratio (VPR): insights into virus–host relationships in a variety of ecosystems

“…As for extreme environments, the available information on viruses in aggregates is scarce, especially in river systems (Peduzzi & Luef, 2008). High viral numbers have been recorded on aggregates, ranging from 10 5 to 3 × 10 11 particles ml −1 Peduzzi, 2015).…”

Virus ecology of fluvial systems: a blank spot on the map?

“…The high degree of spatial heterogeneity in such systems (e.g. backwaters with often lacustrine conditions) also plays a role (Peduzzi & Luef, , ; Jacquet et al ., ; Ma et al ., ). Finally, virus abundance apparently varies more on seasonal scales in inland waters than in the marine environment (Wilhelm & Matteson, ).…”

Abundance and Biomass Responses of Microbial Food Web Components to Hydrology and Environmental Gradients within a Floodplain of the River Danube

“…As well as bacterioplankton, other members of the microbial community are affected by the variability in the system. Peduzzi and Luef [43] showed that abundance of virus-like particles was increased in conditions of hydrological isolation, and therefore could exert an impact on target microorganisms [48,56]. Traditionally, bacterioplankton abundance is considered to be under the control of heterotrophic nanoflagellates [7], as this component of the microbial food web has similar growth rates to bacteria.…”