ON THE ROLE OF THE CYTOSKELETON IN COCCOLITH MORPHOGENESIS: THE EFFECT OF CYTOSKELETON INHIBITORS¹

Abstract

The coccolithophore Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler was cultured in natural seawater with the addition of either the microtubuleinhibitor colchicine, the actin-inhibitor cytochalasin B, or the photosynthesis inhibitor 3-(3,4 dichlorophenyl)-1,1-dimethyl-urea (DCMU). Additionally, E. huxleyi was cultured at different light intensities and temperatures. Growth rate was monitored, and coccolith morphology analyzed. While every treatment affected growth rate, the percentage of malformed coccoliths increased with colchicine, cytochalasin B, and at higher than optimal temperature. These results represent the first experimental evidence for the role of microtubules and actin microfilaments in coccolith morphogenesis.

Phosphorus limitation and heat stress decrease calcification in <i>Emiliania huxleyi</i>

“…Although a similar decrease in growth rate was not observed in batch culture, measurements of growth rate in semi-continuous cultures are more robust because growth rate is measured as an average of numerous dilution cycles. The doubling in coccolith malformations provides further evidence that 24 • C cultures were heat-stressed (Watabe and Wilbur, 1966;Langer et al, 2010;Milner et al, 2016).…”

“…In all of the above studies, however, growth rate increased from low to high temperature and none of the tested temperatures were therefore above the optimum for growth (Eppley, 1972). To our knowledge, this study is the first to show that heat stress is not only detrimental for coccolith morphology (Watabe and Wilbur, 1966;Langer et al, 2010;Milner et al, 2016) but also for coccolith production in E. huxleyi. Certainly, the potential for long-term adaptation needs to be considered, as temperature increases are unlikely to occur on timescales short enough to preclude adaptation in a rapidly growing species.…”

“…Only a few studies have specifically dealt with the effect of temperature on the occurrence of coccolith malformations. These studies suggest that higher than optimum temperature leads to an increase in malformations (Watabe and Wilbur, 1966;Langer et al, 2010). Although the effect of temperature on carbon production in E. huxleyi has been addressed in numerous studies (Sorrosa et al, 2005;Feng et al, 2008;Satoh et al, 2009;De Bodt et al, 2010;Borchard et al, 2011;Sett et al, 2014;Matson et al, 2016;Milner et al, 2016;Rosas- Navarro et al, 2016), none of these studies tested the effect of above-optimum temperature.…”

“…Despite the high percentage of partially dissolved coccoliths in Plimited batch culture, the detrimental effect of heat stress on morphogenesis is evident. As all E. huxleyi strains tested so far show this response, it could be widespread if not ubiquitous (Watabe and Wilbur, 1966;Langer et al, 2010; this study). Interestingly, we observed similar malformations e.g.…”

“…In addition, coccolith ballast can accelerate the removal of organic carbon from upper water layers and aid long-term burial of carbon (Ziveri et al, 2007). Many studies have therefore addressed the production of organic and inorganic carbon (calcite) in E. huxleyi, as well as its modification by environmental factors such as carbonate chemistry (Riebesell et al, 2000;Meyer and Riebesell, 2015), nutrient availability (Paasche and Brubak, 1994;Langer and Benner, 2009), temperature (Watabe and Wilbur, 1966;Langer et al, 2010), salinity (Paasche et al, 1996;Green et al, 1998) and light (Paasche, 1968(Paasche, , 1999.…”