Cyanobacteria facilitate parasite epidemics in Daphnia.

The seasonal dominance of cyanobacteria in the phytoplankton community of lake ecosystems can have severe implications for higher trophic levels. For herbivorous zooplankton such as Daphnia, cyanobacteria have poor nutritional value and some species can produce toxins affecting zooplankton survival and reproduction. Here we present another, hitherto largely unexplored aspect of cyanobacteria, namely that they can increase Daphnia susceptibility to parasites. In a 12-yr monthly time-series analysis of the Daphnia community in Greifensee (Switzerland), we observed that cyanobacteria density correlated significantly with the epidemics of a common gut parasite of Daphnia, Caullerya mesnili, regardless of what cyanobacteria species was present or whether it was colonial or filamentous. The temperature from the previous month also affected the occurrence of Caullerya epidemics, either directly or indirectly by the promotion of cyanobacterial growth. A laboratory experiment confirmed that cyanobacteria increase the susceptibility of Daphnia to Caullerya, and suggested a possible involvement of cyanotoxins or other chemical traits of cyanobacteria in this process. These findings expand our understanding of the consequences of toxic cyanobacterial blooms for lake ecosystems and might be relevant for epidemics experienced by other aquatic species.

Ensembles of data-efficient vision transformers as a new paradigm for automated classification in ecology.

Monitoring biodiversity is paramount to manage and protect natural resources. Collecting images of organisms over large temporal or spatial scales is a promising practice to monitor the biodiversity of natural ecosystems, providing large amounts of data with minimal interference with the environment. Deep learning models are currently used to automate classification of organisms into taxonomic units. However, imprecision in these classifiers introduces a measurement noise that is difficult to control and can significantly hinder the analysis and interpretation of data. We overcome this limitation through ensembles of Data-efficient image Transformers (DeiTs), which not only are easy to train and implement, but also significantly outperform the previous state of the art (SOTA). We validate our results on ten ecological imaging datasets of diverse origin, ranging from plankton to birds. On all the datasets, we achieve a new SOTA, with a reduction of the error with respect to the previous SOTA ranging from 29.35% to 100.00%, and often achieving performances very close to perfect classification. Ensembles of DeiTs perform better not because of superior single-model performances but rather due to smaller overlaps in the predictions by independent models and lower top-1 probabilities. This increases the benefit of ensembling, especially when using geometric averages to combine individual learners. While we only test our approach on biodiversity image datasets, our approach is generic and can be applied to any kind of images.

Biological effect of the Planktothrix sp. FP1 cyanobacterial extract.

Cyanobacteria are common and potentially harmful inhabitants of freshwater and marine environments worldwide. Some waterbloom-forming cyanobacteria are toxic and they may cause animal death and adversely affect human health. A filamentous freshwater cyanobacterium, Planktothrix sp. FP1, was found to be responsible for a toxic algal bloom in Lake Varese (Italy) during August of 1997. In the present study, the biological effects of the Planktothrix sp. FP1 cell extract on Xenopus embryos and on human Peripheral Blood Mononuclear Cells (PBMC) were investigated. FETAX (Frog Embryo Teratogenesis Assay-Xenopus) showed that the cyanobacterial extract had no teratogenic potential, though embryotoxicity was detected (LC(50) 2.944g/l wet weight). The same extract inhibited the proliferation of PBMC stimulated in vitro by phytohemagglutinin (PHA), and strongly interfered with the production of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma).

The purine degradation pathway: possible role in paralytic shellfish toxin metabolism in the cyanobacterium Planktothrix sp. FP1.

The paralytic shellfish toxins (PSTs) are potent neurotoxic alkaloids and their major biological effect is due to the blockage of voltage-gated sodium channels in excitable cells. They have been recognised as an important health risk for humans, animals, and ecosystems worldwide. The metabolic pathways that lead to the production and the degradation of these toxic metabolites are still unknown. In this study, we investigated the possible link between PST accumulation and the activation of the metabolism that leads to purine degradation in the filamentous freshwater cyanobacterium Planktothrix sp. FP1. The purine catabolic pathway is related to the nitrogen microcycle in water environments, in which cyanobacteria use traces of purines and ureides as a nitrogen source for growth. Thus, the activity of allantoicase, a key inducible enzyme of this metabolism, was used as tool for assaying the activation of the purine degradation pathway. The enzyme and the pathway were induced by allantoic acid, the direct substrate of allantoicase, as well as by adenine and, to a lower degree, by urea, one of the main products of purine catabolism. Crude cell extract of Escherichia coli was also employed and showed the best induction of allantoicase activity. In culture, Planktothrix sp. FP1 showed a differential accumulation of PST in consequence of the induction with different substrates. The cyanobacterial culture induced with allantoic acid accumulated 61.7% more toxins in comparison with the control. On the other hand, the cultures induced with adenine, urea, and the E. coli extract showed low PST accumulation, respectively, 1%, 38%, and 5% of the total toxins content detected in the noninduced culture. A degradation pathway for the PSTs can be hypothesised: as suggested for purine alkaloids in higher plants, saxitoxin (STX) and derivatives may also be converted into xanthine, urea, and further to CO2 and NH4+ or recycled in the primary metabolism through the purine degradation pathway.

Microorganisms' activity and energy fluxes in Lake Varese (Italy): a field method.

Microorganisms are fundamental components of energy fluxes in aquatic ecosystems. Interest in plankton production and respiration has recently stimulated exploration of the use of electron transfer system (ETS) activity in oceanography and limnology. If we consider microorganism production (MP) and microorganism respiration (MR), due to aerobic and anaerobic metabolism, microorganism growth efficiency can be defined as MGE = MP/(MP + MR). In order to calculate MGE, we measured independently the two components of ETS (photosynthesis electron transfer system activity (PETS) and respiration electron transfer system activity (RETS)) during an annual cycle using a portable biosensor microorganisms amperometric detector system (MiDAS) on the site. MGE was calculated in samples collected from the photic and aphotic zones and the superficial sediment and ranged between 0.60 and 0.45 and dropped to 0.15 at the end of the summer. This substantial decrease is probably due to the prevalence of the anaerobic-heterotrophic metabolism after a pronounced state of anoxia during the summer algal bloom.