Non-photochemical quenching, a non-invasive probe for monitoring microalgal grazing: an early indicator of predation by Oxyrrhis marina and Euplotes sp.

Abstract

Microalgae are major primary producers in aquatic environments, and many synthesize an array of industrially important biomolecules such as pigments, lipids and proteins. As a result, there is considerable interest in and effort into growing algae for industrial purposes. An economical method to produce a large amount of biomass is the use of the open-raceway pond cultivation platform. However, the nature of the cultivation and the nutrient-rich profile of such cultures attract contaminants such as zooplankton predators, which can result in a sudden culture crash. For effective pond management, an early indicator of grazer presence is needed to implement timely interventions. Currently available tools are offline, time-consuming and dependent on predator concentration. This study explores grazingmediated changes in photosynthetic parameters during infestation of Dunaliella tertiolecta cultures by the heterotrophic dinoflagellate Oxyrrhis marina and the ciliate Euplotes sp. A significant reduction in non-photochemical quenching levels 24-48 h prior to the crash was observed in both bulk and singlecell prey samples. An increasing rate of grazer ingestion correlated with decreasing non-photochemical quenching levels as the culture progressed towards the crash. The reductions in the non-photochemical quenching levels were consistent in grazing cultures at different prey cell concentrations. Although the maximum photosynthetic yield remained unaltered, maximum relative electron transport rates were enhanced and the light-harvesting efficiency, alpha, reduced in comparison to controls. We suggest that, along with traditional methods, non-photochemical quenching monitoring could be used as a part of integrative pest management to minimize predator outbreaks.

Non-photochemical quenching, a non-invasive probe for monitoring microalgal grazing: influence of grazing-mediated total ammonia-nitrogen

“…Ammonia affects photosynthetic parameters such as NPQ, F v /F m , rETR max , light harvesting efficiency (alpha) and Q A reoxidation kinetics (Cao et al, 2013;MacLachlan et al, 1994;Markou et al, 2016). Deore et al (2020) report a reduction in the NPQ levels as a function of active predation by O. marina. However, the photosynthetic quantum efficiency F v /F m remains unaffected, which suggests that the overall photochemistry of PSII was unaltered.…”

“…Chlorophyll a fluorescence, measured using a Walz PhytoPAM II, was used to derive the photosynthetic parameters F v /F m , rETR max , alpha and NPQ as described in Deore et al (2020). To investigate the effects of ammonium chloride on NPQ levels, a healthy D. tertiolecta culture was treated with increasing concentrations of ammonium chloride, 0-50 mM, and incubated in the dark for 5 min prior to recording the chlorophyll a fluorescence response.…”

“…To investigate the effects of ammonium chloride on NPQ levels, a healthy D. tertiolecta culture was treated with increasing concentrations of ammonium chloride, 0-50 mM, and incubated in the dark for 5 min prior to recording the chlorophyll a fluorescence response. All the mentioned parameters were computed using equations described in Deore et al (2020). Q A re-oxidation kinetics were recorded using a PSI FL-3000 Fluorometer (Photon System Instruments, Drasov, Czech Republic).…”

“…However, for their timely implementation, early grazer-detection methods are essential. Deore et al (2020) demonstrated that a reduction in non-photochemical quenching (NPQ) levels in an algal prey species, Dunaliella tertiolecta, can indicate an outbreak of a predator, Oxyrrhis marina, 24-48 h prior to a culture crash. In the current study, we investigated whether the predator-mediated interference in full expression of NPQ in D. tertiolecta could be explained by increase in total ammonianitrogen (TAN) in the culture medium.…”

“…Here, we present data that further suggest that monitoring of NPQ profiles in the prey, D. tertiolecta, and the concentration of TAN in the culture in the presence of the predator, Oxyrrhis marina, can help in predicting the onset of a culture crash. In addition to validating the reduction in the level of NPQ (Deore et al, 2020) we also investigated the relationship between predatorprey interactions and other processes such as the maximum quantum yield of PSII (F v /F m ), the maximum relative electron transport rate (rETR max ), Q A reoxidation kinetics and the formation of ROS. The observed decrease in NPQ in the presence of O. marina appears to be associated with an accumulation of TAN, which can be taken up by D. tertiolecta cells.…”