Metacommunity studies on lake bacterioplankton indicate the importance of environmental factors in structuring communities. Yet most of these studies cover relatively small spatial scales. We assessed the relative importance of environmental and spatial factors in shaping bacterioplankton communities across a > 6000 km latitudinal range, studying 48 shallow lowland lakes in the tropical, tropicali (isothermal subzone of the tropics) and tundra climate regions of South America using denaturing gradient gel electrophoresis. Bacterioplankton community composition (BCC) differed significantly across regions. Although a large fraction of the variation in BCC remained unexplained, the results supported a consistent significant contribution of local environmental variables and to a lesser extent spatial variables, irrespective of spatial scale. Upon correction for space, mainly biotic environmental factors significantly explained the variation in BCC. The abundance of pelagic cladocerans remained particularly significant, suggesting grazer effects on bacterioplankton communities in the studied lakes. These results confirm that bacterioplankton communities are predominantly structured by environmental factors, even over a large-scale latitudinal gradient (6026 km), and stress the importance of including biotic variables in studies that aim to understand patterns in BCC.

Resumo A carga psicoemocional gerada com a morte de pacientes é uma das questões mais difíceis de serem enfrentadas na medicina. Este levantamento de dados, de caráter descritivo e abordagem quantitativa, teve como objetivo principal analisar a atitude de médicos e a percepção de estudantes de medicina em relação ao fim da vida. Os dados foram organizados em duas categorias: percepção dos entrevistados quanto à morte e influência da experiência médica para superar o óbito de enfermos. Os resultados mostram que os discentes se sentem despreparados para enfrentar essa realidade, e a vivência profissional é o principal fator de compreensão dos médicos sobre o tema. Conclui-se que a tanatologia e seus desdobramentos são lacuna na formação em medicina, tornando a morte questão crítica e dolorosa da profissão. Aprovação CEP-Fadip CAAE 68401717.6.0000.8063

The understanding of the functional role of aquatic bacteria in microbial food webs is largely dependent on methods applied to the direct visualization and enumeration of these organisms. While the ultrastructure of aquatic bacteria is still poorly known, routine observation of aquatic bacteria by light microscopy requires staining with fluorochromes, followed by filtration and direct counting on filter surfaces. Here, we used a new strategy to visualize and enumerate aquatic bacteria by light microscopy. By spinning water samples from varied tropical ecosystems in a cytocentrifuge, we found that bacteria firmly adhere to regular slides, can be stained by fluorochoromes with no background formation and fast enumerated. Significant correlations were found between the cytocentrifugation and filter-based methods. Moreover, preparations through cytocentrifugation were more adequate for bacterial viability evaluation than filter-based preparations. Transmission electron microscopic analyses revealed a morphological diversity of bacteria with different internal and external structures, such as large variation in the cell envelope and capsule thickness, and presence or not of thylakoid membranes. Our results demonstrate that aquatic bacteria represent an ultrastructurally diverse population and open avenues for easy handling/quantification and better visualization of bacteria by light microscopy without the need of filter membranes.

While microbial aquatic communities are dominated numerically by viruses, both bacterioplankton and phytoplankton play a basal role in the carbon cycle, producing and mineralizing organic matter and driving CO 2 concentrations. Both weak and strong relationships between these 2 microbial groups have been reported for temperate ecosystems. However, data from the tropics and sub-tropics are still scarce, and no consistent pattern regarding the structural microbial connections in these aquatic environments is known so far. We examined bacteria-phytoplankton abundance relationships for tropical freshwaters in comparison to well-studied temperate aquatic ecosystems. We present data on bacterioplankton and phytoplankton abundances in a large data set (1644 samples; lakes, rivers, and reservoirs) from sampling throughout an extensive gradient of latitude (3°N to 33°S) and longitude (35°to 70°W) in tropical waters. We found a generally weak, but significant, relationship between bacterioplankton and phytoplankton abundances and between bacterioplankton and chlorophyll. However, analyzing system by system, we observed an increase in the strength of the relationships (expressed by the determination coefficient, r 2 ), from 0.05 to 0.17 (bacterioplankton and phytoplankton abundances) and from 0.09 to 0.44 (bacterial abundance and chl a). Our data suggest that the in-system ecological drivers (e.g. water temperature, trophic state, and flushing characteristics, i.e. lentic or lotic) determine the bacterioplankton abundance patterns more than other factors such as latitude or system typology. In a global perspective, the comparison between non-tropical and tropical/sub-tropical freshwaters showed that a lower proportion of phytoplankton carbon is transformed into bacterial carbon in the tropics. KEY WORDS: Microbial dynamics · Bacterial-phytoplankton coupling · Tropical waters Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 60: [261][262][263][264][265][266][267][268][269][270][271][272] 2010 plankton and fish through bacterial biomass (Cole et al. 2006). It is generally believed that autochthonous DOM from phytoplankton is more available for bacterial consumption than allochthonous terrestrial DOC (Kritzberg et al. 2005). Bacteria rapidly assimilate phytoplanktonic carbon compared to terrestrial DOC (Chen & Wangersky 1996). In tropical freshwaters, for instance, humic substances are an important energy source for aquatic bacteria (Amado et al. 2006), but this source is probably not very relevant as a carbon source for bacterial production, since consumption of humic substances appears to be mostly channeled through microbial respiration (Farjalla et al. 2009).The dependence of bacterioplankton on autochthonous carbon has been supported by positive relationships between phytoplankton (expressed as chlorophyll a [chl a], cell numbers, or biovolume) and heterotrophic bacteria (expressed as numbers or biomass, Bird & Kalff 1984, Stewart & Fritsen 2004 or production, W...

We evaluated in situ rates of bacterial carbon processing in Amazonian floodplain lakes and mainstems, during both high water (HW) and low water (LW) phases (p < 0.05). Our results showed that bacterial production (BP) was lower and more variable than bacterial respiration, determined as total respiration. Bacterial carbon demand was mostly accounted by BR and presented the same pattern that BR in both water phases. Bacterial growth efficiency (BGE) showed a wide range (0.2–23%) and low mean value of 3 and 6%, (in HW and LW, respectively) suggesting that dissolved organic carbon was mostly allocated to catabolic metabolism. However, BGE was regulated by BP in LW phase. Consequently, changes in BGE showed the same pattern that BP. In addition, the hydrological pulse effects on mainstems and floodplains lakes connectivity were found for BP and BGE in LW. Multiple correlation analyses revealed that indexes of organic matter (OM) quality (chlorophyll-a, N stable isotopes and C/N ratios) were the strongest seasonal drivers of bacterial carbon metabolism. Our work indicated that: (i) the bacterial metabolism was mostly driven by respiration in Amazonian aquatic ecosystems resulting in low BGE in either high or LW phase; (ii) the hydrological pulse regulated the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes mostly driven by OM quality.