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The ability to form biofilms is a functional trait shared by many bacterial species. Biofilms provide bacteria a sheltered environment where the nutrients and oxygen gradients create a heterogeneous matrix and promote cells to differentiate their metabolism and functions according to the position they occupy inside the matrix. Species of the Microcystis genus are among the most common bloom-forming cyanobacteria. They are unicellular microorganisms able to form colonies and to reach high biomass during blooms in lakes, reservoirs and estuaries worldwide. Colonial lifestyle provides several advantages under stressing conditions, including adaptation to different light intensities, protection from toxic substances and grazing, while allowing them to grow when the nutrient supply is low. Although the biology, ecology and colony formation have been extensively recognized in Microcystis spp., the analysis of the progression from unicellular to multicellular phases in this cyanobacterium have been always addressed as individual phenotypic plasticity and rarely as a multi-specific community of interrelated microorganisms. Here, we re-interpreted the evidence coming from different studies about the Microcystis lifestyle and propose a new way to analyze the available information about this cyanobacterial group. We specifically address the characteristics shared by bacterial biofilms and Microcystis colonies and suggest that the morphological changes from single cells to colonies are due to a cascade of events leading to the formation of a multi-specific biofilm. Studying the formation of colonies using this framework would help to better understand the life cycle of Microcystis, its functional relationship with the associated microbiome and the factors triggering microcystin production, helping to design strategies for prevention and control of the blooms caused by these organisms. Taking into account the biology and the ecological strategies of Microcystis, a conceptual model of emergence and decay of these floating multi-specific biofilms is proposed.

This edited book presents eleven chapters addressing the politics of water in Latin America. It brings together contributions from members of the WATERLAT-GOBACIT Network (www.waterlat.org) from Argentina, Brazil, Mexico, the United Kingdom and Uruguay. In addition to academics, the contributors also include members of public sector andcivil society organizationsengaged in debates and activities connected with the democratisation of water politics. The title of the book reflects a concern with the historical processes of appropriation, control, distribution, etc., of water and water-based services, which can be examined as processes of water territorialization, which includes the territorialization of the production of knowledge about water. The chapters cover a range of empirical examples, from the impacts of large-scale water infrastructures andextractivist activities (mining, agribusinesses), the (mis)management of water-related risks and disasters, the complex and conflictive characterof water management in metropolitan areas, the social and political struggles featuring social movements and other actors confrontingpowerful public and private interests in their quest to democratise water politics and management, among other issues.

Addressing ecological and evolutionary processes explaining biodiversity patterns is essential to identify the mechanisms driving community assembly. In the case of bacteria, the formation of new ecologically distinct populations or ecotypes is proposed as one of the main drivers of diversification. New ecotypes arise when mutation in key functional genes or acquisition of new metabolic pathways by horizontal gene transfer allow the population to exploit new resources, making possible their coexistence with parental population. Recently, we have reported the presence of toxic, microcystin-producing organisms from the Microcystis aeruginosa complex (MAC) through a wide environmental gradient (800 km) in South America, ranging from freshwater to estuarine-marine waters. In order to explain this finding, we hypothesize that the success of toxic organisms of MAC in such array of environmental conditions is due to the existence of ecotypes having different environmental preferences. So, we analysed the genetic diversity of microcystin-producing populations of Microcystis aeruginosa complex (MAC) by qPCR and high resolution melting analysis (HRMA) of a functional gene (mcyJ, involved in microcystin synthesis) and explored its relationship with the environmental conditions through the gradient by functional classification and regression trees (fCART). Six groups of mcyJ genotypes were distinguished and selected by different combinations of water temperature, conductivity and turbidity, determining the environmental preferences of each group. Since these groups were based on the basis of similar sequence and ecological characteristics they were defined as ecotypes of toxic MAC. Taking into account that the role of microcystins in MAC biology and ecology has not yet been elucidated, we propose that the toxin might have a role in MAC fitness that would be mainly controlled by the physical environment in a way such that the ecotypes that thrive in the riverine zone of the gradient would be more stable and less influenced by salinity fluctuations than those living at the marine limit of the estuary. These would periodically disappear or being eliminated by salinity increases, depending on the estuary dynamics. Thus, ecotypes generation would be an important mechanism allowing toxic MAC adapting to and succeed in a wide array of environmental conditions.

Las floraciones de cianobacterias tóxicas son un problema mundial. La eutrofización antrópica y la generación de embalses han promovido su desarrollo en la Cuenca del Plata, favoreciendo principalmente al complejo Microcystis aeruginosa (CMA). En este trabajo describimos las floraciones excepcionales de CMA ocurridas en el verano 2019 en la costa del Río de la Plata y Atlántica de Uruguay y discutimos sus mecanismos moduladores en base a datos biológicos, meteorológicos y oceanográficos de muestreos, imágenes satelitales y re-análisis. Las floraciones fueron extensas (Carmelo a Rocha; 500 km) y persistentes (ca.: 4 meses). En todos los casos fueron organismos del CMA con estructura genética similar y su presencia estuvo asociada a niveles cuantificables y elevados de microcistina. En base a las características oceanográficas y la similitud genética entre los organismos, se hipotetiza que las floraciones tienen un origen común, probablemente asociado a tributarios con alta carga de nutrientes y alto tiempo de residencia del agua en la Cuenca baja del Plata. Las precipitaciones extremas generaron caudales récord que transportaron las cianobacterias hasta el Río de la Plata, donde las condiciones de viento y temperatura particulares facilitaron su transporte y arribo a la costa de Rocha, llegando a ambientes de relevancia para la conservación (e.g. Laguna de Rocha).

En este trabajo se evaluó la dinámica y toxicidad de Microcystis spp. en el embalse de Salto Grande en invierno y verano de 2013, así como la diversidad genética de sus poblaciones tóxicas mediante análisis de melting de alta resolución de amplicones del gen mcyJ. La abundancia de células de Microcystis spp. varió entre los distintos sitios y entre estaciones, detectándose una abundancia signifcativamente mayor de células y genotipos tóxicos así como de microcistina-LR en verano. Además, se detectaron dos grupos de genotipos mcyJ (clusters 1 y 2) con diferentes preferencias ambientales. El 1 estuvo integrado por muestras de Microcystis spp. obtenidas en condiciones de bajas temperaturas (? 17,6 °C) y mayor conductividad (~52-58 µS cm-1), presentando bajo número de células y ausencia de microcistina-LR. Las muestras incluidas en el cluster 2 se caracterizaron por ser de verano (temperatura entre 17,6 y 25,9 ºC), presentar menor conductividad (~50-52 µS cm-1), alta abundancia de células y presencia de microcistina-LR. Nuestros resultados sugieren que las poblaciones tóxicas de Microcystis que ?orecen en verano serían diferentes a las que se mantienen durante el invierno y que la temperatura y conductividad del agua serían variables relevantes que controlarían su abundancia y toxicidad.