RESUMEN
Many volatile compounds secreted by bacteria play an important role in the interactions of microorganisms, can inhibit the growth of phytopathogenic bacteria and fungi, can suppress or stimulate plant growth and serve as infochemicals presenting a new type of interspecies communication. In this work, we investigated the effect of total pools of volatile substances and individual volatile organic compounds (VOCs) synthesized by the rhizosphere bacteria Pseudomonas chlororaphis 449 and Serratia plymuthica IC1270, the soil-borne strain P. fluorescens B-4117 and the spoiled meat isolate S. proteamaculans 94 on Arabidopsis thaliana plants. We showed that total gas mixtures secreted by these strains during their growth on Luria-Bertani agar inhibited A. thaliana growth. Hydrogen cyanide synthesis was unnecessary for the growth suppression. A decrease in the inhibition level was observed for the strain P. chlororaphis 449 with a mutation in the gacS gene, while inactivation of the rpoS gene had no effect. Individual VOCs synthesized by these bacteria (1-indecene, ketones 2-nonanone, 2-heptanone, 2-undecanone, and dimethyl disulfide) inhibited the growth of plants or killed them. Older A. thaliana seedlings were more resistant to VOCs than younger seedlings. The results indicated that the ability of some volatiles emitted by the rhizosphere and soil bacteria to inhibit plant growth should be considered when assessing the potential of such bacteria for the biocontrol of plant diseases.
Asunto(s)
Arabidopsis/efectos de los fármacos , Pseudomonas chlororaphis/química , Pseudomonas chlororaphis/genética , Pseudomonas fluorescens/química , Serratia/química , Compuestos Orgánicos Volátiles/toxicidad , Arabidopsis/crecimiento & desarrollo , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Cianuro de Hidrógeno/metabolismo , Carne/microbiología , Mutación , Pseudomonas chlororaphis/metabolismo , Pseudomonas fluorescens/metabolismo , Rizosfera , Plantones/efectos de los fármacos , Serratia/metabolismo , Factor sigma/genética , Factor sigma/metabolismo , Microbiología del Suelo , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Compuestos Orgánicos Volátiles/químicaRESUMEN
Polymorphisms of 62 peroxidase genes derived from Arabidopsis thaliana were investigated to evaluate evolutionary dynamics and divergence of peroxidase proteins. By comparing divergence of duplicated genes AtPrx53-AtPrx54 and AtPrx36-AtPrx72 and their products, nucleotide and amino acid substitutions were identified that were apparently targets of positive selection. These substitutions were detected among paralogs of 461 ecotypes from Arabidopsis thaliana. Some of these substitutions are conservative and matched paralogous peroxidases in other Brassicaceae species. These results suggest that after duplication, peroxidase genes evolved under the pressure of positive selection, and amino acid substitutions identified during our study provided divergence of properties and physiological functions in peroxidases. Our predictions regarding functional significance for amino acid residues identified in variable sites of peroxidases may allow further experimental assessment of evolution of peroxidases after gene duplication.
Asunto(s)
Arabidopsis/enzimología , Arabidopsis/genética , Evolución Molecular , Peroxidasas/genética , Alelos , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Datos de Secuencia Molecular , Peroxidasas/química , Polimorfismo Genético , Selección Genética , Homología de Secuencia de Ácido NucleicoRESUMEN
Cyanobacteria are a group of oxygenic phototrophs existing for at least 3.5 Ga. Photosynthetic CO2 assimilation by cyanobacteria occurs via the Calvin cycle, with RuBisCO, its key enzyme, having very low affinity to CO2. This is due to the fact that atmospheric CO2 concentration in Archaean, when the photosynthetic apparatus evolved, was several orders higher than now. Later, in the epoch of Precambrian microbial communities, CO2 content in the atmosphere decreased drastically. Thus, present-day phototrophs, including cyanobacteria, require adaptive mechanisms for efficient photosynthesis. In cyanobacterial cells, this function is performed by the CO2-concentrating mechanism (CCM), which creates elevated CO2 concentrations in the vicinity of RuBisCO active centers, thus significantly increasing the rate of CO2 fixation in the Calvin cycle. CCM has been previously studied only for freshwater and marine cyanobacteria. We were the first to investigate CCM in haloalkaliphilic cyanobacteria from soda lakes. Extremophilic haloalkaliphilic cyanobacteria were shown to possess a well-developed CCM with the structure and functional principles similar to those of freshwater and marine strains. Analysis of available data suggests that regulation of the amount of inorganic carbon transported into the cell is probably the general CCM function under these conditions.
