Effects of UV Radiation on the Chlorophyte Micromonas polaris Host-Virus Interactions and MpoV-45T Virus Infectivity.

Charlotte Eich,Sven B E H Pont,Corina P D Brussaard

doi:10.3390/microorganisms9122429

Charlotte Eich, Sven B E H Pont + Show 1 more

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https://doi.org/10.3390/microorganisms9122429

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Abstract

Polar seas are under threat of enhanced UV-radiation as well as increasing shipping activities. Considering the ecological importance of marine viruses, it is timely to study the impact of UV-AB on Arctic phytoplankton host–virus interactions and also test the efficacy of ballast water (BW) UV-C treatment on virus infectivity. This study examined the effects of: (i) ecologically relevant doses of UV-AB radiation on Micromonas polaris RCC2258 and its virus MpoV-45T, and (ii) UV-C radiation (doses 25–800 mJ cm−2) on MpoV-45T and other temperate algal viruses. Total UV-AB exposure was 6, 12, 28 and 48 h (during the light periods, over 72 h total). Strongest reduction in algal growth and photosynthetic efficiency occurred for 28 and 48 h UV-AB treatments, and consequently the virus production rates and burst sizes were reduced by more than half (compared with PAR-only controls). For the shorter UV-AB exposed cultures, negative effects by UV (especially Fv/Fm) were overcome without impacting virus proliferation. To obtain the BW desired log−4 reduction in virus infectivity, a UV-C dose of at least 400 mJ cm−2 was needed for MpoV-45T and the temperate algal viruses. This is higher than the commonly used dose of 300 mJ cm−2 in BW treatment.

Highlights

Phytoplankton depend on photosynthetic active radiation (PAR) for their primary production, but are exposed to UV radiation in the surface waters of the ocean [1].Natural UV-radiation reaching the Earth’s surface is a combination of UV-A (315–400 nm) and UV-B (280–315 nm), while UV-C (100–280 nm) is largely absorbed in the Earth’s atmosphere [2]
Exposure of Micromonas polaris to UV-AB up to 28 h led to an initial reduction of the growth of M. polaris, growth resumed when UV-AB exposure was stopped
The growth rates for M. polaris during recovery from 6 to 28 h UV-AB radiation were with 0.16–0.31 d−1 which was largely comparable to the 0.21 ± 0.04 (n = 3) of the PAR-only controls

Summary

Introduction

Phytoplankton depend on photosynthetic active radiation (PAR) for their primary production, but are exposed to UV radiation in the surface waters of the ocean [1].Natural UV-radiation reaching the Earth’s surface is a combination of UV-A (315–400 nm) and UV-B (280–315 nm), while UV-C (100–280 nm) is largely absorbed in the Earth’s atmosphere [2]. The exact concentration of light (both PAR and UV) that phytoplankton in the surface ocean experience, depends on atmospheric ozone depletion, vertical mixing, ice cover, cloud cover and the turbidity of the water [2,3,4]. In the Arctic, the formation of so called ozone holes are more variable, increasing by 10% from 1983 to 2003 [14] and reaching a new maximum in 2020 [15]. These polar ozone depletions occur at the same time as phytoplankton blooms begin [16], and are estimated to decrease annual primary production from 0.25% [17] up to

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