Environmental dynamics as a structuring factor for microbial carbon utilization in a subtropical coastal lagoon

Laguna de Rocha belongs to a series of shallow coastal lagoons located along South America. It is periodically connected to the sea through a sand bar, exhibiting a hydrological cycle where physicochemical and biological gradients are rapidly established and destroyed. Its most frequent state is the separation of a Northern zone with low salinity, high turbidity and nutrient load, and extensive macrophyte growth, and a Southern zone with higher salinity and light penetration, and low nutrient content and macrophyte biomass. This zonation is reflected in microbial assemblages with contrasting abundance, activity, and community composition. The physicochemical conditions exerted a strong influence on community composition, and transplanted assemblages rapidly transformed to resembling the community of the recipient environment. Moreover, the major bacterial groups responded differently to their passage between the zones, being either stimulated or inhibited by the environmental changes, and exhibiting contrasting sensitivities to gradients. Addition of allochthonous carbon sources induced pronounced shifts in the bacterial communities, which in turn affected the microbial trophic web by stimulating heterotrophic flagellates and virus production. By contrast, addition of organic and inorganic nutrient sources (P or N) did not have significant effects. Altogether, our results suggest that (i) the planktonic microbial assemblage of this lagoon is predominantly carbon-limited, (ii) different bacterial groups cope differently with this constraint, and (iii) the hydrological cycle of the lagoon plays a key role for the alleviation or aggravation of bacterial carbon limitation. Based on these findings we propose a model of how hydrology affects the composition of bacterioplankton and of carbon processing in Laguna de Rocha.This might serve as a starting hypothesis for further studies about the microbial ecology of this lagoon, and of comparable transitional systems.Fil: Alonso, Cecilia. Universidad de la República; UruguayFil: Piccini, Claudia. Instituto de Investigaciones Biológicas "Clemente Estable"; UruguayFil: Unrein, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Bertoglio, Florencia. Universidad de la República; UruguayFil: Conde, Daniel. Universidad de la República; UruguayFil: Pernthaler, Jakob. Universitat Zurich; Suiz

A simple and effective method for extracting potential mutagens from sediment samples in the classroom laboratory setting

We describe a simple and effective method for the extraction of potential mutagens from sediment samples. This method is straightforward and does not require expensive laboratory equipment, thus enabling instructors to analyze the presence of mutagenic substances in a conventional classroom setting. Additionally, we found that students felt encouraged to add the Ames test to the list of analyses they traditionally employ with sediment samples. This link between the environment and the Ames test provided an authentic learning context for students, bridging the gap between the "real-world" and the classroom laboratory, and thus making the educational experience more engaging and meaningful

Competition and protist predation are important regulators of riverine bacterial community composition and size distribution

Among the bacterivorous protists, heterotrophic nanoflagellates (HNFs) are considered to be the main grazers of bacteria in freshwaters due to their size-selective grazing. In this work, we assessed the change of a riverine bacterial community in controlled incubations, where HNFs' predation pressure was initially released through filtration. Filtration did not prevent the passage of cysts, which grew in the enrichments afterwards. Data on the composition of the bacterial community were gathered by Catalyzed Reporter Deposition Fluorescent In situ Hybridization (CARD-FISH) using 16S probes targeting phylogenetic groups. Bacterial cell size was also examined using image analysis. Overall, the initial filtration directly (through release of predation pressure) or indirectly (through competition among bacterial groups) affected the bacterial community composition. When nanoflagellate abundance rose, a reduction of bacterial abundance and changes in cell size distribution were observed. Gamma-Proteobacteria and Actinobacteria were the groups showing the greatest reduction in abundance. Beta-Proteobacteria showed a reduction of cell size and were found in aggregates. Alpha-Proteobacteria and Actinobacteria developed two distinct filamentous morphotypes: short, segmented rods and long chains of rods. Our results showed that the release of the predation pressure and the successive rise of the nanoflagellates changed the bacterial community in terms of composition at large phylogenetic scale. HNF grazing is highly group-specific and seems to reconstruct the community based on cell size, and thus, not only drastically changing the bacterial community composition, but also increasing its functional diversity

The bicycle and the dream of a sustainable city: An explorative comparison of the image of bicycles in the mass-media and the general public

This paper explores the representation of the bicycle by comparing data from various mass media sources and the general public in Italy. In study 1, a number of commercial advertisements published on paper magazines and aired by the major TV channels, as well as 405 articles published by the major online newspapers were content analysed in order to identify the main concepts and evaluations characterising the representation of bikes in the media. In study 2, 94 Rome residents were interviewed on their beliefs regarding the pros and cons of using the bike in the city and their perceived social approval. Results showed several points of overlap between the two representations, although different themes and structures emerged as well

Teaching during the COVID-19 Pandemic: sharing results and data obtained from the Ames Test

We present a resource for instructors that contains results and data sets from the Ames test. Our aim is to share the results we have collected in previous semesters with other instructors, so they will be able to “conduct” the Ames test without the need to set foot in a laboratory classroom. Instructors will be able to use our online resource to perform the test remotely, as a supplement to their laboratory classroom, or even under hybrid circumstances. The coronavirus disease 2019 (COVID-19) pandemic brought many changes, including the way we, as instructors, were able to carry out our educational curricula, since access to laboratory classrooms was not always possible. While COVID-19 restrictions are still in place, and thus access to laboratory classrooms is limited or null, instructors can use our online resource, without the need to set foot in a laboratory classroom. When COVID-19 restrictions are lifted and access to laboratory classrooms is permitted, instructors can follow the procedures we describe and compare their results with ours, which appear in Results and Discussion, or use our data sets as take-home assignments for their students. In addition to its use in detecting the potential mutagenicity of different samples, we have found the Ames test to be extremely useful for developing problem-solving skills by means of exercises like the ones included in this resource. Furthermore, the potential of this test as a starting point for problem-based learning is remarkable. Some suggestions for its use in active learning settings are provided

Effects of oral Lactobacillus spp. pretreatment on sensitized response induced by repeated smoked cocaine and the influence on gut microbiota structure

Emerging studies highlight the potential role of intestinal microbiota (IM) modulation in brain disorders; however, studies addressing its involvement in substance use disorder (SUD) are limited. Cocaine systemic administration in rodents induces gut dysbiosis and chronic antibiotics enhance its rewarding property. Accordingly, we demonstrated that repeated exposure to volatilized cocaine (14 days) alters the IM structure and diversity in rats, leading to hypothesized that IM modulation by probiotic bacteria can attenuate cocaine effects. The present study aims to evaluate the role of the IM modulation on the changes induced by the chronic administration of smokable cocaine on locomotor sensitization, and IM structure. Adult male Wistar rats were administered via oral syringe-feeding with a bacterial mixture of three probiotic Lactobacillus strains (L. johnsonii ATCC 33200; L. rhamnosus GG ATCC 53103; L. reuteri ATCC 23272; 1x10E8 CFU in 0.5 ml) or vehicle (skim milk) for 28 days. From day 22 to 28, rats were also daily exposed to cocaine (7 days/25 mg) by pulmonary inhalation, and locomotor activity in the open field was assessed. Fecal samples were collected at different time points and processed for DNA extraction, sequencing and posterior microbiota analysis. Behavioral results showed that oral bacteria administration did not per se affect locomotor activity. In cocaine-exposed rats we observed a progressive stimulant effect (locomotor sensitization) from day 1 to 5 of cocaine, and decreased in days 6 and 7. Bacteria administration did not prevent cocaine sensitization, and maintained the motor activity elevated until the last day. On day 28, no significant differences were found in the microbiota structure in cocaine-exposed animals in comparison with the control group. However, animals administered with bacteria and exposed to cocaine showed differences in their IM structure compared to bacteria control group (p=0.038), and tend to differ concerning the cocaine group (p=0.052). All these results suggest that 7 days of volatilized cocaine are not enough to significantly change IM structure, but an influence of bacterial mixture pretreatment was observed, suggesting a possible role in the sustained cocaine-stimulant effect. Altogether our findings provide information about the role of gut-brain axis in SUD. Further experiments should be done to evaluate the potential benefits of other bacterial strains for microbial-based therapeutic strategy in SUD.Agencia Nacional de Investigación e InnovaciónPEDECIB