RESUMEN
Biosurfactants are produced by hydrocarbon-degrading marine bacteria in response to the presence of water-insoluble hydrocarbons. This is believed to facilitate the uptake of hydrocarbons by bacteria. However, these diffusible amphiphilic surface-active molecules are involved in several other biological functions such as microbial competition and intra- or inter-species communication. We report the isolation and characterization of a marine bacterial strain identified as Cobetia sp. MM1IDA2H-1, which can grow using the sulfur-containing heterocyclic aromatic hydrocarbon dibenzothiophene (DBT). As with DBT, when the isolated strain is grown in the presence of a microbial competitor, it produces a biosurfactant. Because the obtained biosurfactant was formed by hydroxy fatty acids and extracellular lipidic structures were observed during bacterial growth, we investigated whether the biosurfactant at its critical micelle concentration can interfere with bacterial communication systems such as quorum sensing. We focused on Aeromonas salmonicida subsp. salmonicida, a fish pathogen whose virulence relies on quorum sensing signals. Using biosensors for quorum sensing based on Chromobacterium violaceum and Vibrio anguillarum, we showed that when the purified biosurfactant was mixed with N-acyl homoserine lactones produced by A. salmonicida, quorum sensing was inhibited, although bacterial growth was not affected. In addition, the transcriptional activities of A. salmonicida virulence genes that are controlled by quorum sensing were repressed by both the purified biosurfactant and the growth in the presence of Cobetia sp. MM1IDA2H-1. We propose that the biosurfactant, or the lipid structures interact with the N-acyl homoserine lactones, inhibiting their function. This could be used as a strategy to interfere with the quorum sensing systems of bacterial fish pathogens, which represents an attractive alternative to classical antimicrobial therapies in fish aquaculture.
Asunto(s)
Aeromonas salmonicida/efectos de los fármacos , Antibacterianos/metabolismo , Halomonadaceae/metabolismo , Percepción de Quorum/efectos de los fármacos , Tensoactivos/metabolismo , Aeromonas salmonicida/genética , Aeromonas salmonicida/metabolismo , Aeromonas salmonicida/fisiología , Técnicas Biosensibles , Biotransformación , Chromobacterium/efectos de los fármacos , Chromobacterium/fisiología , Perfilación de la Expresión Génica , Halomonadaceae/clasificación , Halomonadaceae/genética , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , Tiofenos/metabolismo , Vibrio/efectos de los fármacos , Vibrio/fisiología , Factores de Virulencia/metabolismoRESUMEN
A total of 52 strains of moderately halophilic bacteria isolated from hypersaline sediment of Lake Tebenquiche on the Atacama Saltern, Chile, were subjected to a taxonomic study. The morphological, physiological, biochemical and nutritional characteristics of the strains matched those described for the genus Chromohalobacter. Cells were Gram-negative, non-spore-forming, rod-shaped and motile. A black pigmentation was produced. One strain, designated LTS-4N(T), grew optimally at 32 degrees C. Growth occurred in media containing 0.5-25% (w/v) total salts; the optimum was 7.5% (w/v) total salts. The pH range for growth was 5-10. The G + C content of the DNA of strain LTS-4N(T) was 59.8 mol%. Analysis of 16S rRNA gene sequence similarity revealed that strain LTS-4N(T) was closely related to Chromohalobacter species; however, DNA-DNA hybridization of representative strain LTS-4N(T) failed to associate the strain with any species of the genus Chromohalobacter with validly published names. Therefore, the name Chromohalobacter nigrandesensis sp. nov. is proposed. The type strain is LTS-4N(T) (= CECT 5315T = DSM 14323T).
Asunto(s)
Agua Dulce/microbiología , Halomonadaceae/clasificación , Chile , ADN Ribosómico/química , Halomonadaceae/genética , Halomonadaceae/aislamiento & purificación , Halomonadaceae/fisiología , Fenotipo , Filogenia , ARN Ribosómico 16S/genéticaRESUMEN
A moderately halophilic, aerobic, motile, Gram-negative, rod-shaped bacterium (strain LV4(T)) was isolated from saline soil around the lake Laguna Verde in the Bolivian Andes. The organism is a heterotroph, able to utilize various carbohydrates as a carbon source. It showed tryptophan deaminase, oxidase and catalase activity, but was unable to produce indole or H(2)S; nitrate was not reduced. The G+C content of the genomic DNA was 56.1 mol%. The pH range for growth was 5-10, temperature range was 0-45 degrees C and the range of NaCl concentrations was 0-25 % (w/v). On the basis of 16S rRNA gene sequence analysis, strain LV4(T) was found to be closely related to Chromohalobacter canadensis DSM 6769(T) and Pseudomonas beijerinckii DSM 7218(T); however, its DNA-DNA relatedness with these type strains was low. Strain LV4(T) resembled other Chromohalobacter species with respect to various physiological, biochemical and nutritional characteristics but also exhibited differences. Thus, a novel species, Chromohalobacter sarecensis sp. nov., is proposed, with LV4(T) (=CCUG 47987(T)=ATCC BAA-761(T)) as the type strain.