There is a vivid debate on the relative importance of local and regional factors in shaping microbial communities, and on whether microbial organisms show a biogeographic signature in their distribution. Taking a metacommunity approach, spatial factors can become important either through dispersal limitation (compare large spatial scales) or mass effects (in case of strongly connected systems). We here analyze two datasets on bacterial communities [characterized by community fingerprinting through denaturing gradient gel electrophoresis (DGGE)] in meso-to eutrophic shallow lakes to investigate the importance of spatial factors at three contrasting scales. Variation partitioning on datasets of both the bacterial communities of 11 shallow lakes that are part of a strongly interconnected and densely packed pond system <1 km apart, three groups of shallow lakes Ϸ100 km apart, as well as these three groups of shallow lakes combined that span a large part of a North-South gradient in Europe (>2,500 km) shows a strong impact of local environmental factors on bacterial community composition, with a marginal impact of spatial distance. Our results indicate that dispersal is not strongly limiting even at large spatial scales, and that mass effects do not have a strong impact on bacterial communities even in physically connected systems. We suggest that the fast population growth rates of bacteria facilitate efficient species sorting along environmental gradients in bacterial communities over a very broad range of dispersal rates. dispersal limitation ͉ metacommunity biology ͉ microbial biogeography ͉ microbial community ͉ mass effects
To understand mechanisms of tufa biofilm calcification, selected karstwater stream stromatolites in Germany have been investigated with regard to their hydrochemistry, biofilm community, exopolymers, physicochemical microgradients, calcification pattern and lamination. In stream waters, CO2 degassing drives the increase in calcite saturation to maximum values of approximately 10-fold, independent from the initial Ca2+/alkalinity ratio. For the cyanobacteria of tufa biofilms, a culture-independent molecular approach showed that microscopy of resin-embedded biofilm thin sections underestimated the actual diversity of cyanobacteria, i.e. the six cyanobacteria morphotypes were opposed to nine different lineages of the 16S rDNA phylogeny. The same morphotype may even represent two genetically distant cyanobacteria and the closest relatives of tufa biofilm cyanobacteria may be from quite different habitats. Diatom diversity was even higher in the biofilm at the studied exemplar site than that of the cyanobacteria, i.e. 13 diatom species opposed to 9 cyanobacterial lineages. The non-phototrophic prokaryotic biofilm community is clearly different from the soil-derived community of the stream waters, and largely composed of flavobacteria, firmicutes, proteobacteria and actinobacteria. The exopolymeric biofilm matrix can be divided into three structural domains by fluorescence lectin-binding analysis. Seasonal and spatial variability of these structural EPS domains is low in the investigated streams. As indicated by microsensor data, biofilm photosynthesis is the driving mechanism in tufa stromatolite formation. However, photosynthesis-induced biofilm calcification accounts for only 10–20% of the total Ca2+ loss in the streams, and occurs in parallel to inorganic precipitation driven by CO2-degassing within the water column and on biofilm-free surfaces. Annual stromatolite laminae reflect seasonal changes in temperature and light supply. The stable carbon isotope composition of the laminae is not affected by photosynthesis-induced microgradients, but mirrors that of the bulk water body only reflecting climate fluctuations. Tufa stromatolites with their cyanobacterial–photosynthesis-related calcification fabrics form an analogue to porostromate cyanobacterial stromatolites in fossil settings high in CaCO3 mineral supersaturation but comparatively low in dissolved inorganic carbon. Here, the sum-effect of heterotrophic exopolymer-degradation and secondary Ca2+-release rather decreases calcite saturation, contrary to settings high in dissolved inorganic carbon such as soda lakes.
During a survey to determine the prevalence of Aeromonas strains in water and skin of imported ornamental fish, 48 strains presumptively identified as Aeromonas were isolated but they could not be identified as members of any previously described Aeromonas species. These strains were subjected to a polyphasic approach including phylogenetic analysis derived from gyrB, rpoD and 16S rRNA gene sequencing, DNA-DNA hybridization, MALDI-TOF MS analysis, genotyping by RAPD and extensive biochemical and antibiotic susceptibility tests in order to determine their taxonomic position. Based on the results of the phylogenetic analyses and DNA-DNA hybridization data, we describe a novel species of the genus Aeromonas, for which the name Aeromonas aquariorum sp. nov. is proposed, with strain MDC47 T (5DSM 18362 T 5CECT 7289 T ) as the type strain. This is the first Aeromonas species description based on isolations from ornamental fish.Species of Aeromonas are common inhabitants of aquatic environments and have been described in connection with fish and human diseases (Altwegg, 1999;Austin & Adams, 1996;Saavedra et al., 2004;Figueras, 2005). Apart from the psychrophilic suspected fish pathogen Aeromonas salmonicida, many other mesophilic aeromonads are considered to be opportunistic pathogens, capable of producing infections in weakened fish or as secondary invaders in fish populations suffering from other diseases (Camus et al., 1998). Given the large numbers of ornamental fish imported from areas of the world where sanitation is often inadequate and where numerous diseases of man are endemic, it is surprising that little consideration has been given to the role of these aquarium species as vectors of potential pathogens for man. When the occurrence of bacterial pathogens in ornamental fish has been investigated, Aeromonas strains were found in more than 50 % of fish disease cases examined by Kuo & Chung (1994) and were involved in 18 of 23 bacterial disease outbreaks investigated by Hettiarachchi & Cheong (1994). Moreover, noticeable antibiotic resistance has been detected in Aeromonas strains isolated from ornamental fish (Dixon & Issvoran, 1992).The genus Aeromonas belongs to the family Aeromonadaceae (Colwell et al., 1986;Martínez-Murcia et al., 1992a; Yáñez et al., 2003). According to the last edition of Bergey's Manual of Systematic Bacteriology (Martin-Carnahan & Joseph, 2005), the genus comprises the species Aeromonas hydrophila, A. bestiarum, A. salmonicida, A. caviae, A. media, A. eucrenophila, A. sobria, A. veronii (biovars Sobria and Veronii), A. jandaei, A. schubertii, A. trota, A. allosaccharophila, A. encheleia and A. popoffii and two DNA homology groups, Aeromonas sp. HG11 and Aeromonas sp. HG13 (formerly enteric group 501), which remain without a species name. Furthermore, Aeromonas ichthiosmia (Schubert et al., 1990b) and Aeromonas enteropelogenes (Schubert et al., 1990a) are now considered synonyms of A. veronii and A. trota, respectively (Carnahan, 1993;Collins et al., 1993;Huys et al., 2001Huys et al., ,...
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