The hydrocarbon-degrading marine bacterium Cobetia sp. strain MM1IDA2H-1 produces a biosurfactant that interferes with quorum sensing of fish pathogens by signal hijacking

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

Predicting the effects of biochar on volatile petroleum hydrocarbon biodegradation and emanation from soil: a bacterial community finger-print analysis inferred modelling approach

We investigated the response of the dominant bacterial taxa in gravelly sand to the addition of biochar and/or mixtures of volatile petroleum hydrocarbons (VPHs) using denaturing gradient gel electrophoresis (DGGE) and sequencing of cut bands. Biochar addition alone had only weak effects on the soil bacterial community composition in batch study samples, while VPH addition had strong effects. Indirect effects of biochar on soil bacterial communities were apparent in column study samples, where biochar-enhanced sorption affected VPH spreading. Following VPH addition, cell abundance increased by no more than a factor of 2 and several Pseudomonas spp. became dominant in soil with and without biochar. We present a VPH fate model that considers soil bacterial biomass dynamics and a nutrient limited soil biomass carrying capacity. The model simulates an apparent lag phase before the onset of a brief period of intensive VPH biodegradation and biomass growth, which is followed by substantially slower VPH biodegradation, when nitrogen needs to be recycled between decaying and newly formed biomass. If biomass growth is limited by a factor other than the organic pollutant bioavailability, biochar amendment may enhance VPH attenuation in between a VPH source below ground and the atmosphere by reducing the risk of overloading the soil's biodegradation capacity

Diagnóstico de alteraciones tipo Dag-defect en cerdos

Sobre la base de 225 verracos examinados se entrega la incidencia porcentual de alteraciones tipo 'Dag-defect'. Se concluye que el 7,2% acusa más de 10% de anomalías espermáticas tipo 'Dag-defect', mientras que el 2,7% muestra más del 25% de tales anormalidades. Por intermedio de las alteraciones de la motilidad espermática, presencia de gota citoplasmática, colas anormales a la microscopía de luz, y la ausencia de ricrotúbulos y del axonema a la microscopía electrónica, se diagnostica la presencia en Chile de 'Dag-defect' en cerdos importados o sus descendientes

Diagnóstico de alteraciones tipo Dag-defect en cerdos

Sobre la base de 225 verracos examinados se entrega la incidencia porcentual de alteraciones tipo 'Dag-defect'. Se concluye que el 7,2% acusa más de 10% de anomalías espermáticas tipo 'Dag-defect', mientras que el 2,7% muestra más del 25% de tales anormalidades. Por intermedio de las alteraciones de la motilidad espermática, presencia de gota citoplasmática, colas anormales a la microscopía de luz, y la ausencia de ricrotúbulos y del axonema a la microscopía electrónica, se diagnostica la presencia en Chile de 'Dag-defect' en cerdos importados o sus descendientes