Phosphorus limitation affects the molecular composition of Thalassiosira weissflogii leading to increased biogenic silica dissolution and high degradation rates of cellular carbohydrates

Abstract

Diatoms in general, and Thalassiosira weissflogii (T. weissflogii) in particular, are among the most ubiquitous phytoplanktonic species while, phosphorus (P) is an essential nutrient that limits productivity in many oceanic regimes. To investigate how T. weissflogii cultures grown under different P regimes are chemically altered before and during their prokaryotic degradation, T. weissflogii cells were cultivated under two contrasting P conditions, "P-stress" and "P-replete". Biodegradation experiments were conducted in natural seawater comprising a natural prokaryotic community. The particulate fraction was monitored for 3 weeks for organic carbon (POC), nitrogen (PON), biogenic silica (bSiO 2), total carbohydrates (PCHO) and individual monosaccharides, including prokaryotic counting. Our results indicated that P-stress induced changes in the chemical composition of the T. weissflogii cells, causing a decrease to the Si/N (1.1 to 0.46) and Si/C (0.17 to 0.08) ratios. The "P-stress T. weissflogii" cells were characterized by high amounts of galactose (23% of PCHO), xylose (21%), and glucose (19%) compared to the "P-replete T. weissflogii" cells, which were dominated by ribose (20% of PCHO), further indicating the exhaustion of riboserich molecules (e.g., ATP) in T. weissflogii under "P-stress" conditions. The degradation experiments showed that bSiO 2 produced under "P-stress" conditions dissolved more rapidly than bSiO 2 formed under "P-replete" conditions, whereas POC and PON exhibited higher degradation rate constants in the "P-replete T. weissflogii" than in the "P-stress T. weissflogii" experiment. Overall, these observations show that T. weissflogii submitted to P-limitation, results in changes in its initial biochemical composition, increases frustule dissolution rate, and decreases the degradation of T. weissflogii-organic matter by marine prokaryotes.

Modeling the elemental stoichiometry and silicon accumulation in diatoms

“…Si:N and Si:P vary due to the existence of storage when the respective nutrients are not limited. Additionally, the lower Si:C values at lower growth rates when P is limited correspond to previous laboratory studies that observed increasing absolute C under P limitation ( Obata et al., 2013 ; Brembu et al., 2017 ; Panagiotopoulos et al., 2020 ). Lastly, there is large variation between the two modeled nutrient regimes in N:P (Fig.…”

Increasing Hydrostatic Pressure Impacts the Prokaryotic Diversity during Emiliania huxleyi Aggregates Degradation

“…Most of the deep North Atlantic sediments consist of rich calcareous materials composed of coccolithophores, such as E. huxleyi, implying a significant role for these organisms in efficient export [16,17]. The presence of "ballast" minerals (such as opal, calcium carbonate, or dust) has been proposed to preserve the organic matter from biotic degradation [18][19][20][21][22][23]. Prokaryotic-mediated diatom silica dissolution has been found to increase together with the degradation of organic matter in surface waters [24][25][26] and to decrease with decreasing temperature [27].…”

Multi-Element Composition of Diatom Chaetoceros spp. from Natural Phytoplankton Assemblages of the Russian Arctic Seas

“…For example, when seven strains of microalgae (Amphiprora paludosa, Cyclotella cryptica, C. meneghiniana, Navicula incerta, Nitzschia laevis, Thalassiosira guillardii, and T. weissflogii) were cultivated under laboratory conditions, the change in illumination intensity resulted in six-fold variation in BSi content between species and twofold variation within one species, even if the concentration and ratio of nutrients were stable and optimal [58]. A similar dependence of BSi accumulation on environmental factors was observed in different species of diatoms, namely on temperature [52,59], concentration of macronutrients [60][61][62], essential elements [63,64], and various metals [65,66].…”