Bec, A. | bioRxiv Science

bioRxiv2025

Temperature dependent response of microcystin-LR in acclimated Microcystis aeruginosa: highest content expected near the growth optimum

As climate change raises global temperatures and increases the frequency of cyanobacterial blooms, understanding how rising mean temperatures affect cyanotoxin content is crucial. However, no clear consensus exists, and the use of different methodologies, including different units of measurement and experimental conditions could significantly alter the yield of the relationship between temperature and toxins content. In this study, we assessed free microcystin content and cell volume in Microcystis aeruginosa PCC 7806 acclimated to seven temperatures spanning its entire thermal niche. This experimental design firstly highlighted the significant reduction in cell volume with rising temperatures between 17{degrees}C and 29{degrees}C. As a result, when the microcystin concentration was normalized by its cell volume, its temperature response was transformed from a negative correlation to a bell-shaped curve, with higher free MC-LR content measured at an estimated optimum temperature of 26.2{degrees}C, close to the thermal growth optimum of Microcystis aeruginosa. These findings provide new insights into the effects of climate warming on microcystin content. ImportanceMicrocystin-LR is a widespread cyanotoxin, originally known for its liver toxicity. In freshwater environments, cyanotoxins are an increasing concern as harmful cyanobacterial blooms become more frequent with rising global temperatures. Microcystis aeruginosa, a common bloom-forming species found worldwide, is a major producer of microcystin-LR. Understanding how environmental factors such as temperature influence toxin content in this species is essential for predicting bloom toxicity under future climate scenarios. However, current knowledge remains fragmented due to numerous factors that can influence its production and also to different way of measuring toxins and expressing their concentrations (cell or {micro}m3). Confirming that temperature greatly modifies biovolume of M. aeruginosa, this study offers new insights by highlighting the importance of considering cell volume when evaluating toxin content. Integrating changes in cell size helps reconcile earlier conflicting results and contributes to a more accurate understanding of how temperature affects toxin production in cyanobacteria. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=176 HEIGHT=200 SRC="FIGDIR/small/660678v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@7a591org.highwire.dtl.DTLVardef@6eb39org.highwire.dtl.DTLVardef@3d0f19org.highwire.dtl.DTLVardef@aa6be0_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2019

The Threshold Elemental Ratio of an ectotherm decreases then increases with rising temperature

Earth is currently facing unprecedented global changes, hurrying scientists to provide predictive tools to explore the futures responses of ecosystems. Among those changes, temperature increase and alterations of nutrient availabilities largely drive consumer performances, yet their interactive effect remains poorly understood. Here we investigate how the dietary C:P ratio that optimizes consumer growth (TERC:P: Threshold Elemental Ratio) changes along temperature gradients by combining a TERC:P model and growth experiments on the model organism Daphnia magna. Both lines of evidence show that the TERC:P responds to temperature in an U-shaped fashion. This shape reconciles previous contradictive observations into a common framework, thereby improving our capacity to forecast the combined effects of nutrient cycle and climatic alterations on ectotherms.

ecology↗

bioRxiv2018

A microcalorimetric approach for investigating stoichiometric constraints on the standard metabolic rate of a small invertebrate

1: Understanding the determinant of metabolism is a core ecological topic since it permits to link individuals energetic requirements to the ecology of communities and ecosystems. Yet, besides temperature, the effects of environmental factors on metabolism remain poorly understood. For example, dietary stoichiometric constraints have been hypothesized to increase maintenance metabolism of small invertebrates, yet experimental support remains scarce.\n\n2: Here, we used microcalorimetric heat flow measurements to determine the standard metabolic rate (SMR) of Daphnia magna throughout its ontogeny when fed stoichiometrically balanced (C/P ratio:166) or imbalanced (C/P ratio:1439) diets.\n\n3: When fed a stoichiometrically imbalanced diet, daphnids were able to maintain the stoichiometric homeostasis within narrow boundaries. However, they consistently increased their SMR while decreasing their somatic growth rate. Our measurements unequivocally demonstrate that homeostatic regulation implies higher metabolic costs and thereby reduces the portion of energy that can be allocated to growth.\n\n4: Our study demonstrates that microcalorimetry is a powerful and precise tool for measuring the metabolic rate of small-sized organisms and opens promising perspectives for understanding how environmental factors, such as nutritional constraints, affect organismal metabolism.

ecology↗