RESUMEN
Dissolved organic matter (DOM) and heterotrophic bacteria are highly diverse components of the ocean system, and their interactions are key in regulating the biogeochemical cycles of major elements. How chemical and phylogenetic diversity are linked remains largely unexplored to date. To investigate interactions between bacterial diversity and DOM, we followed the response of natural bacterial communities to two sources of phytoplankton-derived DOM over six bacterial generation times in continuous cultures. Analyses of total hydrolysable neutral sugars and amino acids, and ultrahigh resolution mass spectrometry revealed large differences in the chemical composition of the two DOM sources. According to 454 pyrosequences of 16S ribosomal ribonucleic acid genes, diatom-derived DOM sustained higher levels of bacterial richness, evenness and phylogenetic diversity than cyanobacteria-derived DOM. These distinct community structures were, however, not associated with specific taxa. Grazing pressure affected bacterial community composition without changing the overall pattern of bacterial diversity levels set by DOM. Our results demonstrate that resource composition can shape several facets of bacterial diversity without influencing the phylogenetic composition of bacterial communities, suggesting functional redundancy at different taxonomic levels for the degradation of phytoplankton-derived DOM.
Asunto(s)
Bacteroidetes/genética , Proteobacteria/genética , Agua de Mar/microbiología , Cianobacterias/química , Diatomeas/química , Genes Bacterianos , Fenómenos Microbiológicos , Microbiota/genética , Compuestos Orgánicos/química , Compuestos Orgánicos/metabolismo , Filogenia , Fitoplancton/química , ARN Ribosómico 16S/genética , Agua de Mar/química , SolucionesRESUMEN
Isolates showing different and similar colony morphologies were selected from spread plates of bacteria from seawater samples taken in the northern Adriatic Sea. All isolates were characterised by restriction fragment length polymorphism (RFLP) patterns of their PCR-amplified 16S rRNA gene and by 95 physiological tests (Biolog system). Cluster analysis of both genetic and phenotypic patterns showed that different colony morphotypes were related to different species or biotypes. However, isolates belonging to the more well-defined, conspicuous colony types had a high similarity, whereas those from the less conspicuous colony morphotypes showed high genetic diversity. Although colony morphotypes clearly underestimate taxonomic diversity, they can be used combined with PCR-RFLP analysis and as a preliminary approach for ecological studies aimed at the isolation of different species. Furthermore, for some species forming very conspicuous pigmented colonies, such as some photosynthetic aerobic bacteria, colony morphology may be useful for a rapid and low-cost screening of their distribution in the natural environment, especially when combined with other molecular techniques.