Production and characterization of a trehalolipid biosurfactant produced by the novel marine bacteriumRhodococcussp., strain PML026

AIMS: The aim of this study was to evaluate biosurfactant production by a novel marine Rhodococcus sp., strain PML026 and characterize the chemical nature and properties of the biosurfactant. METHODS AND RESULTS: A novel marine bacterium (Rhodococcus species; strain PML026) was shown to produce biosurfactant in the presence of hydrophobic substrate (sunflower oil). Biosurfactant production (identified as a trehalolipid) was monitored in whole-batch cultures (oil layer and aqueous phase), aqueous phase (no oil layer) and filtered (0·2mum) aqueous phase (no oil or cells; extracellular) and was shown to be closely associated with growth/biomass production. Extracellular trehalolipid levels increased postonset of stationary growth phase. Purified trehalolipid was able to reduce the surface tension of water to 29mN m(-1) at Critical Micellar Concentration (CMC) of c. 250mgl(-1) and produced emulsions that were stable to a wide range of conditions (pH 2-10, temperatures of 20-100°C and NaCl concentrations of 5-25% w/v). Separate chemical analyses of the intact trehalolipid and its constituents demonstrated the compound was in fact a mixture of homologues (>1180MW) consisting of a trehalose moiety esterified to a series of straight chain and hydroxylated fatty acids. CONCLUSIONS: The trehalolipid biosurfactant produced by the novel marine strain Rhodococcus sp. PML026 was characterized and exhibited high surfactant activity under a wide range of conditions. SIGNIFICANCE AND IMPACT OF STUDY: Strain PML026 of Rhodococcus sp. is a potential candidate for bioremediation or biosurfactant production for various applications.

The origin of sub-surface source waters define the sea-air flux of methane in the Mauritanian Upwelling, NW Africa

Concentrations and flux densities of methane were determined during a lagrangian study of an advective filament in the permanent upwelling region off western Mauritania. Newly upwelled waters were dominated by the presence of North Atlantic Central Water and surface CH4 concentrations of 2.2 ± 0.3 nmol L-1 were largely in equilibrium with atmospheric values, with surface saturations of 101.7 ± 14%. As the upwelling filament aged and was advected offshore, CH4 enriched South Atlantic Central Water from intermediate depths of 100 to 350m was entrained into the surface mixed layer of the filament following intense mixing associated with the shelf break. Surface saturations increased to 198.9 ± 15% and flux densities increased from a mean value over the shelf of 2.0 ± 1.1 µmol m-2d-1 to a maximum of 22.6 µmol m-2d-1. Annual CH4 emissions for this persistent filament were estimated at 0.77 ± 0.64 Gg which equates to a maximum of 0.35% of the global oceanic budget. This raises the known outgassing intensity of this area and highlights the importance of advecting filaments from upwelling waters as efficient vehicles for air-sea exchange.