Virus-Bacterium Coupling Driven by both Turbidity and Hydrodynamics in an Amazonian Floodplain Lake

Author:

Barros Nathan1,Farjalla Vinicius F.2,Soares Maria C.3,Melo Rossana C. N.4,Roland Fábio1

Affiliation:

1. Laboratory of Aquatic Ecology, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil, CEP 36036-900

2. Laboratory of Limnology, Department of Ecology, Institute of Biology, CCS-UFRJ, P.O. Box 68020, Rio de Janeiro, Brazil, CEP 21941-590

3. Department of Sanitary and Environmental Engineering, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil, CEP 36036-900

4. Laboratory of Cell Biology, Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil, CEP 36036-900

Abstract

ABSTRACT The importance of viruses in aquatic ecosystem functioning has been widely described. However, few studies have examined tropical aquatic ecosystems. Here, we evaluated for the first time viruses and their relationship with other planktonic communities in an Amazonian freshwater ecosystem. Coupling between viruses and bacteria was studied, focusing both on hydrologic dynamics and anthropogenic forced turbidity in the system (Lake Batata). Samples were taken during four hydrologic seasons at both natural and impacted sites to count virus-like particles (VLP) and bacteria. In parallel, virus-infected bacteria were identified and quantified by transmission electron microscopy (TEM). Viral abundance ranged from 0.5 × 10 7 ± 0.2 × 10 7 VLP ml −1 (high-water season, impacted site) to 1.7 × 10 7 ± 0.4 × 10 7 VLP ml −1 (low-water season, natural site). These data were strongly correlated with the bacterial abundance ( r 2 = 0.84; P < 0.05), which ranged from 1.0 × 10 6 ± 0.5 × 10 6 cells ml −1 (high water, impacted site) to 3.4 × 10 6 ± 0.7 × 10 6 cells ml −1 (low water, natural site). Moreover, the viral abundance was weakly correlated with chlorophyll a , suggesting that most viruses were bacteriophages. TEM quantitative analyses revealed that the frequency of visibly infected cells was 20%, with 10 ± 3 phages per cell section. In general, we found a low virus-bacterium ratio (<7). Both the close coupling between the viral and bacterial abundances and the low virus-bacterium ratio suggest that viral abundance tends to be driven by the reduction of hosts for viral infection. Our results demonstrate that viruses are controlled by biological substrates, whereas in addition to grazing, bacteria are regulated by physical processes caused by turbidity, which affect underwater light distribution and dissolved organic carbon availability.

Publisher

American Society for Microbiology

Subject

Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology

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