RESUMO
The anoxygenic phototrophic bacteria (APB) are an active component of aquatic microbial communities. While DNA-based studies have delivered a detailed picture of APB diversity, they cannot provide any information on the activity of individual species. Therefore, we focused on the expression of a photosynthetic gene by APB communities in two freshwater lakes (Cep lake and the Rímov Reservoir) in the Czech Republic. First, we analyzed expression levels of pufM during the diel cycle using RT-qPCR. The transcription underwent a strong diel cycle and was inhibited during the day in both lakes. Then, we compared DNA- (total) and RNA-based (active) community composition by sequencing pufM amplicon libraries. We observed large differences in expression activity among different APB phylogroups. While the total APB community in the Rímov Reservoir was dominated by Betaproteobacteria, Alphaproteobacteria prevailed in the active library. A different situation was encountered in the oligotrophic lake Cep where Betaproteobacteria (order Burkholderiales) dominated both the DNA and RNA libraries. Interestingly, in Cep lake we found smaller amounts of highly active uncultured phototrophic Chloroflexi, as well as phototrophic Gemmatimonadetes. Despite the large diversity of APB communities, light repression of pufM expression seems to be a common feature of all aerobic APB present in the studied lakes.
Assuntos
Proteínas de Bactérias/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Lagos/microbiologia , Microbiota/fisiologia , Fotoperíodo , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Alphaproteobacteria/isolamento & purificação , Alphaproteobacteria/fisiologia , Alphaproteobacteria/efeitos da radiação , Proteínas de Bactérias/genética , Betaproteobacteria/isolamento & purificação , Betaproteobacteria/fisiologia , Betaproteobacteria/efeitos da radiação , República Tcheca , DNA Bacteriano/genética , DNA Bacteriano/isolamento & purificação , Regulação Bacteriana da Expressão Gênica/efeitos da radiação , Luz/efeitos adversos , Microbiota/efeitos da radiação , Complexo de Proteínas do Centro de Reação Fotossintética/genética , Processos Fototróficos/genética , Processos Fototróficos/efeitos da radiação , FilogeniaRESUMO
For heterotrophic microorganisms (44 strains) isolated-from the surface film of Lake Baikal, iden- tification was carried out and their. physiological and biochemical characteristics were determined. Com- pared to the water column, diversity of cultured heterotrophs was low, indicating formation of stable micro- bial communities at the air-water interphase interface. Heterotrophic bacteria isolated from the surface mi- crolayer exhibited the enzymatic activity comparable to that for strains form other biofilm associations. Deinococcusfi6us strain NA202 'vas the most active component of the community, capable of utilization of the broadest spectrum of mono- and disaccharides,'sugars, and amino acids. This strain possessed the highest diversity of extracellular enzymes and was the most resistant to UV radiation. The physiological and bio- chemical properties of this strain may-be responsible for its adaptation to survival in extreme conditions of the surface microlayer. Our results improve our understanding of occurrence of UV-resistant strains in freshwater ecosystems.
Assuntos
Deinococcus/metabolismo , Processos Heterotróficos/fisiologia , Lagos/microbiologia , Consórcios Microbianos/fisiologia , Filogenia , RNA Ribossômico 16S/genética , Alphaproteobacteria/classificação , Alphaproteobacteria/genética , Alphaproteobacteria/isolamento & purificação , Alphaproteobacteria/efeitos da radiação , Aminoácidos/metabolismo , Bacteroidetes/classificação , Bacteroidetes/genética , Bacteroidetes/isolamento & purificação , Bacteroidetes/efeitos da radiação , Betaproteobacteria/classificação , Betaproteobacteria/genética , Betaproteobacteria/isolamento & purificação , Betaproteobacteria/efeitos da radiação , Biodiversidade , Deinococcus/classificação , Deinococcus/isolamento & purificação , Deinococcus/efeitos da radiação , Deltaproteobacteria/classificação , Deltaproteobacteria/genética , Deltaproteobacteria/isolamento & purificação , Deltaproteobacteria/efeitos da radiação , Dissacarídeos/metabolismo , Ecossistema , Firmicutes/classificação , Firmicutes/genética , Firmicutes/isolamento & purificação , Firmicutes/efeitos da radiação , Gammaproteobacteria/classificação , Gammaproteobacteria/genética , Gammaproteobacteria/isolamento & purificação , Gammaproteobacteria/efeitos da radiação , Processos Heterotróficos/efeitos da radiação , Consórcios Microbianos/efeitos da radiação , Monossacarídeos/metabolismo , Proteobactérias/classificação , Proteobactérias/genética , Proteobactérias/isolamento & purificação , Proteobactérias/efeitos da radiação , Sibéria , Propriedades de Superfície , Raios UltravioletaRESUMO
Deletion of two of the major electron carriers, the reaction center-bound tetrahemic cytochrome and the HiPIP, involved in the light-induced cyclic electron transfer pathway of the purple photosynthetic bacterium, Rubrivivax gelatinosus, significantly impairs its anaerobic photosynthetic growth. Analysis on the light-induced absorption changes of the intact cells of the mutants shows, however, a relatively efficient photo-induced cyclic electron transfer. For the single mutant lacking the reaction center-bound cytochrome, we present evidence that the electron carrier connecting the reaction center and the cytochrome bc(1) complex is the High Potential Iron-sulfur Protein. In the double mutant lacking both the reaction center-bound cytochrome and the High Potential Iron-sulfur Protein, this connection is achieved by the high potential cytochrome c(8). Under anaerobic conditions, the halftime of re-reduction of the photo-oxidized primary donor by these electron donors is 3 to 4 times faster than the back reaction between P(+) and the reduced primary quinone acceptor. This explains the photosynthetic growth of these two mutants. The results are discussed in terms of evolution of the type II RCs and their secondary electron donors.
Assuntos
Betaproteobacteria/efeitos da radiação , Citocromos/metabolismo , Evolução Molecular , Luz , Mutação/genética , Fotossíntese/efeitos da radiação , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Absorção/efeitos da radiação , Proteínas de Bactérias/metabolismo , Betaproteobacteria/citologia , Betaproteobacteria/crescimento & desenvolvimento , Espectroscopia de Ressonância de Spin Eletrônica , Transporte de Elétrons/efeitos da radiação , Elétrons , Deleção de Genes , Heme/metabolismo , Modelos Moleculares , Fotossíntese/genética , Ligação Proteica/efeitos da radiação , Fatores de TempoRESUMO
The recA and the recX genes of Herbaspirillum seropedicae were sequenced. The recX is located 359 bp downstream from recA. Sequence analysis indicated the presence of a putative operator site overlapping a probable sigma70-dependent promoter upstream of recA and a transcription terminator downstream from recX, with no apparent promoter sequence in the intergenic region. Transcriptional analysis using lacZ promoter fusions indicated that recA expression increased three- to fourfold in the presence of methyl methanesulfonate (MMS). The roles of recA and recX genes in the SOS response were determined from studies of chromosomal mutants. The recA mutant showed the highest sensitivity to MMS and UV, and the recX mutant had an intermediate sensitivity, compared with the wild type (SMR1), confirming the essential role of the RecA protein in cell viability in the presence of mutagenic agents and also indicating a role for RecX in the SOS response.