Some Mixotrophic Flagellate Species Selectively Graze on Archaea.

Many phototrophic flagellates ingest prokaryotes. This mixotrophic trait becomes a critical aspect of the microbial loop in planktonic food webs because of the typical high abundance of these flagellates. Our knowledge of their selective feeding upon different groups of prokaryotes, particularly under field conditions, is still quite limited. In this study, we investigated the feeding behavior of three species (Rhodomonas sp., Cryptomonas ovata, and Dinobryon cylindricum) via their food vacuole content in field populations of a high mountain lake. We used the catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) protocol with probes specific for the domain Archaea and three groups of Eubacteria: Betaproteobacteria, Actinobacteria, and Cytophaga-Flavobacteria of Bacteroidetes Our results provide field evidence that contrasting selective feeding exists between coexisting mixotrophic flagellates under the same environmental conditions and that some prokaryotic groups may be preferentially impacted by phagotrophic pressure in aquatic microbial food webs. In our study, Archaea were the preferred prey, chiefly in the case of Rhodomonas sp., which rarely fed on any other prokaryotic group. In general, prey selection did not relate to prey size among the grazed groups. However, Actinobacteria, which were clearly avoided, mostly showed a size of <0.5 µm, markedly smaller than cells from the other groups. IMPORTANCE: That mixotrophic flagellates are not randomly feeding in the main prokaryotic groups under field conditions is a pioneer finding in species-specific behavior that paves the way for future studies according to this new paradigm. The particular case that Archaea were preferentially affected in the situation studied shows that phagotrophic pressure cannot be disregarded when considering the distribution of this group in freshwater oligotrophic systems.

Validation of PM10 and PM2.5 early alert in Bogotá, Colombia, through the modeling software WRF-CHEM.

Air quality data from Bogotá, Colombia, show high levels of particulate matter (PM), which often generate respiratory problems to the population and a high economic cost to the government. Since 2016, air quality in the city of Bogotá has been measured through the Bogota Air Quality Index (IBOCA) which works as an indicator of environmental risk due to air pollution. However, available technological tools in Bogotá are not enough to generate early alerts due to PM10 and PM2.5. Currently, alerts are only announced once the measured PM values exceed a certain standard (e.g., 37 µ g/m3), but not with enough anticipation to efficiently protect the population. It is necessary to develop an early air quality alert in Bogotá, in order to provide information that improves risk management protocols in the capital district. The purpose of this investigation is to validate the corrective alert presented on the 14th and 15th of February of 2019, through the WRF-Chem model under different weather conditions, using three different setups of the model to simulate PM10 and PM2.5 concentrations during two different climatic seasons and different resolutions. The results of this article generate a validation of two configurations of the model that can be used for the Environmental Secretary of the District (SDA) forecasts in Bogotá, Colombia, in order to contribute to the prediction of pollution events produced by PM10 and PM2.5 as a tool for an early alert system (EAS) at least 24 h in advance.

Experimental evidence of the quantitative relationship between the prokaryote ingestion rate and the food vacuole content in mixotrophic phytoflagellates.

The verification that many phytoflagellates ingest prokaryotes has changed the view of the microbial loop in aquatic ecosystems. Still, progress is limited because the phagotrophic activity is difficult to quantify in natural assemblages. Linking the food vacuole content in protist with the ingestion rate of prokaryotes would provide a crucial step forward. In this study, using the catalysed reporter deposition - fluorescence in situ hybridization protocol (CARD-FISH), which allows the visualization of labelled prokaryotes inside protists without relying on incubation procedures, we experimentally relate the food vacuole content of prokaryotes (Vc ) to the population-averaged ingestion rates (Ir ) estimated using bacteria-size fluorescent microspheres. The two variables relate according to the equation Ir = 7.52 Vc 0.9 , which indicates a prokaryote half-life of about 6 min in the protist vacuole. Five mixotrophic flagellate species from natural and culture populations were evaluated seven times during 24 h; they provided a broad range of average vacuole content (0.01 to 2.02 prokaryote protist-1 ) and ingestion rates (0.18 to 23 prokaryote protist-1 h-1 ). Consequently, the relationship found can be applied to quantify the mixotrophy activity in a large variety of field and experimental studies.