This study investigates the spatial distribution of viruses and prokaryotes in the central Indian Ocean. Samples were collected during cruise MR19-04. Samples for microbial enumeration were determined by flow cytometry. Prokaryotic cell and virus particle densities varied by up to three orders of magnitude (4.3 x 10³ - 1.3 x 10⁶ cells mL^-1) and one order of magnitude (2.4 x 10⁵ - 8.3 x 10⁶ particles mL^-1), respectively. The vertical distribution of the ratio of virus to prokaryote density showed a monotonically increasing trend with depth at all stations. In the surface layer the ratio was 10.2 ± 5.7 (mean ± SD, n = 145), while in the mesopelagic layer it was 14.3 ± 9.8 (n = 153). In the bathypelagic layer the mean ratio was 27.4 ± 14.2 (n = 219) and in the bottom layer 39.6 ± 19.6 (n = 56). The mean values in the bathypelagic and bottom layers were higher and more variable than those in the surface and mesopelagic layers. This variability is mainly due to the horizontal (latitudinal) variation of the ratio. These results suggest that the distribution patterns of viruses and prokaryotes in the central Indian Ocean differ between depth layers. These differences can be attributed to the different mechanisms of reproduction and decay of viruses and prokaryotes. In particular, the latitudinal variation in the ratio in the bathypelagic and the bottom layer (increasing from high to low latitudes) is likely to be explained by the fact that virus particles are less easily removed from the environment (less easily degraded) than prokaryotic cells.

Primary Presenter: Taichi Yokokawa, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) (taichi.yokokawa@jamstec.go.jp)

Authors:

Masahito Shigemitsu, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)  (ma-shige@jamstec.go.jp)