PNNL

Abstract

The Amazon River watershed and its associated plume comprise a vast continental and oceanic area. The microbial activities along this continuum contribute substantially to global carbon and nutrient cycling, yet there is a dearth of information on the diversity, abundance, and possible roles of viruses in this globally important river. The aim of this study was to elucidate the diversity and structure of virus assemblages of the Amazon river-ocean continuum. Environmental viral DNA sequences were obtained for twelve locations along the river’s lower reach (five) and plume (seven). Sequence assembly yielded 29,358 scaffolds, encoding 82,546 viral proteins, with 15 new complete viral genomes. Despite the spatial connectivity mediated by the river, virome analyses and physical-chemical water parameters clearly distinguished river and plume ecosystems. Bacteriophages were ubiquitous in the continuum, and more abundant in the transition region. Eukaryotic viruses occurred mostly in the river, while the plume had more viruses of autotrophic organisms (Prochlorococcus, Synechococcus) and heterotrophic bacteria (Pelagibacter). The viral families Microviridae and Myoviridae were the most abundant and occurred throughout the continuum. Viral structural and life cycle genes were the major functions in the continuum, and viruses from plume locations and Tapajós River showed highest functional diversity. The distribution patterns of the viral assemblages were defined not only by the occurrence of possible hosts, but also by water physical and chemical parameters, especially salinity. The findings presented here help to understand the possible roles of viruses in the organic matter cycle along the river-ocean continuum.