Relationship between viral and prokaryotic abundance on the Bajo O’Higgins 1 Seamount (Humboldt Current System off Chile)

Abstract

SUMMARY: There is little known about the ecology of microbial communities living in the water column over seamounts. Here, for the first time, the spatial distribution and abundance of virus-like particles (VLP) are described over a seamount. The association between VLP distribution, prokaryotic abundance, and environmental variables is also analyzed. Sampling was conducted in December 2004 on the Bajo O'Higgins 1 seamount (32°54'S, 73°53'W) located in the Humboldt Current System off Chile. A oxygen minimum layer (OMZ) was clearly present between 130 and 280 m in the water column over the seamount. Water samples were taken with Niskin bottles at 10 oceanographic stations over the seamount at depths of 5, 20, 50, 75, 100, and 150 m and at the benthic boundary layer (BBL; 5-12 m over the sediments). Temperature, salinity, oxygen, chlorophyll a, and phaeopigments were measured at each station. Viral and prokaryotic abundances were determined with fluorochrome SYBR Green I. Viral abundance ranged from 1.53 x 10 9 VLP L -1 -16.48 x 10 9 VLP L -1 , whereas prokaryotic abundance ranged from 1.78 x 10 8 cell L -1 -14.91 x 10 8 cell L -1 . The virus-like particle/prokaryote ratio varied widely among the analyzed layers (i.e. surface, OMZ, and BBL), probably due to the presence of different prokaryotic and viral assemblages in each layer. Our results indicate that the environmental conditions, mainly the concentration of dissolved oxygen in the water column over Bajo O'Higgins 1 seamount, shape the association between viral and prokaryotic abundance.Keywords: virus-like particles, prokaryotes, seamount, oxygen minimum zone, benthic boundary layer, Humboldt Current System. RESUMEN: RELACIÓN ENTRE LA ABUNDANCIA VIRAL Y PROCARIÓTICA SOBRE EL MONTE SUBMARINO BAJO O'HIGGINS 1 (SISTEMA DE LA CORRIENTE DE HUMBOLDT FRENTE A CHILE). -La ecología de comunidades microbianas que habitan en la columna de agua sobre montes submarinos es escasamente conocida. Aquí, por primera vez, se describe la distribución y abundancia de partículas virales (VLP) sobre un monte submarino. La asociación entre la distribución de VLP, abundancia de procariotas y variables ambientales es también analizada. El muestreo fue realizado en Diciembre del 2004 sobre el monte submarino Bajo O'Higgins 1 (32°54'S, 73°53'W) localizado en el Sistema de la Corriente de Humboldt frente a Chile. Una zona de mínimo oxígeno se detectó entre 130 y 280 m en la columna de agua sobre el monte submarino. Las muestras de agua fueron tomadas con botellas Niskin desde 10 estaciones oceanográficas a 5, 20, 50, 75, 100, y 150 m de profundidad y en la capa de interfase bentónica (BBL; 5-12 m sobre el sedimento). Las variables temperatura, salinidad, oxígeno, clorofila a y feopigmentos fueron medidas en cada estación. La abundancia de virus y procariotas se determinó utilizando el fluorocromo SYBR Green I. La abundancia viral varió entre 1.53 x 10 9 VLP L -1 -16.48 x 10 9 VLP L -1 , mientras que la abundancia de células procariotas lo hizo entre 1.78 x 10 8 células L -1 -14.91 x 10 ...

Study of Virioplankton Abundance and Morphological Diversity in a Brazilian Coastal Region Influenced by Upwelling System

“…The virus to bacteria ratios (VBR) observed in this study (1.17 to 5.93) didn't fell in the range of values recorded for tropical waters, once we found a low VBR ratio (Figure 2). One of the reasons to explain this fact could be a non-significant rate of infection, either a low number of viruses by host cell, or high virus decay rate [17,56] . Besides those, another alternative hypothesis for the low VBR may be due specifically to viral infection on its host [65,66] .…”

“…Several studies on virus abundance and distribution have been performed in polar regions as the Arctic [11][12][13] and Antarctica [8,14] , and also in different temperate and tropical ocean portions, as Pacific [9,15,16] and Atlantic [4,17,18] . However, few virus ecology studies have addressed the assessment of virioplankton community in tropical aquatic ecosystems [4,19] .…”

Virioplankton distribution in the tropical western Pacific Ocean in the vicinity of a seamount

“…At present, little is known about the influences of seamounts on virioplankton. In the only known study on virioplankton distributions in seamounts, Chiang and Quiñones (2007) stated that comparatively elevated viral and HP abundances were detected in the benthic‐boundary layer over the Bajo O'Higgins 1 seamount summit. However, taking the depth differences between summit (376 m) and other stations (437–841 m) into account, the higher VLP abundance might not be completely attributed to the influence of seamount.…”

“…Further, virioplankton have received the least attention of all members of this microbial community. To the best of our knowledge, only the spatial virioplankton abundance for the Bajo O'Higgins 1 seamount (32°54′S, 73°53′W) has been reported (Chiang & Quiñones, 2007). Viral abundance and production have been explored in the deep‐sea sediments around two seamounts at 3,000‐m depth in the Tyrrhenian Sea (Danovaro et al, 2009).…”

Colonial life under the Humboldt Current System: deep sea corals from O Higgins I seamount

“…Scarce oxygen levels reflect the influence of the Equatorial Subsurface Water (ESSW) associated to an oxygen-minimum zone (OMZ). Below this layer, the Antarctic Intermediate Water (IAW) is responsible for low temperatures and higher oxygen levels, which increased to a maximum of almost 4 mL O 2 L -1 around 550 m depth (Chiang & Quiñones, 2007). On the summit of O'Higgins I seamount (400 to 500 m depth), oceanographic conditions were: temperatures from 5.8 to 6.9ºC, dissolved oxygen from 2 to 3 mL O 2 L -1 and the salinity ≈34.3 psu (Chiang & Quiñones, 2007).…”