New Light on the Scaling of Metabolic Rate With the Size of Algae

Abstract

The scaling of metabolic rate with the size of algae has been discussed and researched at length. The observation that algae usually have exponents b in the equation R ϭ a ؒ W Ϫ b (where R is the specific growth rate, W is the organism [cell] biomass, and a and b are constants) equal to or higher than the value of Ϫ 0.25 for many other organisms is generally related to resource-saturated (maximal) values of R. Recent work has shown that the exponent b for lightlimited growth is more negative than Ϫ 0.25. This was predicted from considerations of the package effect in photon absorption, as modulated by the volumespecific pigment content of the cells, and the photosynthetic unit size. Further work is needed to extrapolate these findings to fluctuating light environments. This minireview puts the recent work into a broader context and suggests how further work could quantify the roles of optical thickness and of spatial and temporal variations in the radiation field in determining metabolic rates.

Genome analysis of the smallest free-living eukaryote Ostreococcus tauri unveils many unique features

“…However, genes putatively encoding all of the enzymes required for C 4 photosynthesis were identified (see Table 10). Whereas C 4 photosynthesis has yet to be unequivocally shown in unicellular organisms (24,25,37,38), C 4 in the absence of Kranz anatomy is now well documented, especially in Hydrilla verticillata, a facultative C 4 aquatic monocot (39). Unlike T. pseudonana, which appears to lack plastid-localized NADP-dependent malic enzymes (NADP-ME), O. tauri has two NADP-ME orthologs most similar to H. verticillata (40) with at least one apparently targeted to the chloroplast based on ChloroP and TargetP predictions.…”

“…Much less is known about eukaryotic phytoplankton, because only one, the diatom Thalassiosira pseudonana, has a complete genome sequenced (24). Picoeukaryotes are especially interesting in the context of marine primary production, given the combination of their broad environmental distribution and the fact that their surface area to volume ratio, a critical factor in resource acquisition and success in oligotrophic environments (25), is similar to that of prokaryotic counterparts generally considered superior in uptake and transport of nutrients.…”

A Novel Mechanism, Linked to Cell Density, Largely Controls Cell Division in Synechocystis

“…Considering that the metabolism does not control the rate of cell division, we tested whether already known factors were responsible, such as (1) nutrient starvation (Lazazzera, 2000;Berla and Pakrasi, 2012), (2) quorum sensing (Sharif et al, 2008), and (3) reduction of light quality and intensity available to the cells due to high cell density (self-shading; Raven and Kübler, 2002;Ort and Melis, 2011;Lea-Smith et al, 2014).…”

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

“…The maximum attainable daily growth rate of large phytoplankton, P , was calculated using an exponential temperature function (Bissinger et al, 2008;Eppley, 1972). Based on allometric theory (Raven and Kübler, 2002) the maximum growth rate of small phytoplankton was set to be 30% higher than that of large phytoplankton. The half saturation constants for the uptake of ammonium and nitrate by phytoplankton were used to tune (optimize) the model.…”