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

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.

Changes in infectious titer of Black sea algal virus of the microalgae tetraselmis viridis under the influence of a constant magnetic field

In three experiments aimed at studying the effect of a constant magnetic field with a magnetic induction of 600 G and a duration of experiments of 24 and 36 h, it was found that with a low initial titer of the algal virus of the microalgae Tetraselmis viridis, its stay in a magnetic field for 24 h led to an increase in the infectious titer by one order of magnitude. However, when the virus with a higher infectious titer was in a magnetic field for 24 h, no changes in the titer were observed, and after 36 h, its decrease by one order of magnitude was recorded. The results obtained indicate the need for further research in this direction, with using a wider range of algal viruses.

Monitoring of Black Sea algal viruses Tetraselmis viridis and Phaeodactylum tricornutum in bays of Sevastopol as a component of ecological monitoring of the studied aquatories

Virus monitoring is a widespread control of their background circulation. Since 2002, the monitoring of algal viruses that infect microalgae Tetraselmis viridis and Phaeodactylum tricornutum has been carried out in the bays of Sevastopol differing in ecological conditions. The purpose of this work is to analyze and assess the results of this long-term (2002–2020) monitoring. The results obtained with taking into account the exactingness or resistance to environmental conditions of hosts of algal viruses that infect microalgae T. viridis and P. tricornutum were the basis for the following conclusions regarding the ecological well-being of the studied bays of Sevastopol: – relatively favorable ecological conditions in 2007–2008, 2017–2018 and in 2020. (maximum frequency of isolation PtV, and/or minimum TvV, and / or maximum difference in frequency of isolation between PtV and TvV); – unfavorable ecological conditions in 2002–2003, 2006 and 2015 (maximum frequency of isolation TvV, and/or minimum PtV, and/or maximum difference in frequency of isolation between TvV and PtV). Analysis of the monitoring results of algal viruses of T. viridis and P. tricornutum in 2015–2020 revealed that the studied relatively ecologically safe bays are characterized by the maximum number of all isolates of algal viruses (both TvV and PtV) and the numerical predominance of strains of algal virus of P. tricornutum, which is demanding to environmental conditions. At the same time, the minimum amount of all viral isolates was recorded in the ecologically unfavorable bay. The results of a long-term monitoring of algal viruses of T. viridis and P. tricornutum have established the possibility of using the monitoring of marine viruses, in particular of algal viruses of microalgae which are indicative of the ecological situation, as a component of complex ecological monitoring as ecological indicator.