Phenanthrene degradation in soils co-inoculated with phenanthrene-degrading and biosurfactant-producing bacteria

Contaminant sorption within the soil matrix frequently limits biodegradation. However, contaminant bioavailability can be species-specific. This study investigated bioavailability of phenanthrene (PHE) to two PHE-degrading bacteria (Pseudomonas strain R and isolate P5-2) in the presence of rhamnolipid biosurfactant and/or a biosurfactant-producing bacterium, Pseudomonas aeruginosa ATCC 9027. Pseudomonas strain R mineralized more soil-sorbed PHE than strain P5-2, but in aqueous cultures the rate and extent of PHE mineralization by P5-2 exceeded that by P. strain R. In Fallsington sandy loam (fine-loamy, mixed, active, mesic Typic Endoaquult) (high PHE-sorption capacity) the addition of rhamnolipid increased PHE mineralization by P. strain R. Phenanthrene mineralization in soils inoculated with P5-2 was minimal and no enhancement in PHE degradation was observed when biosurfactant was added. Co-inoculation of Fallsington sandy loam with the biosurfactant producer did not affect PHE mineralization by isolate P5-2, but significantly enhanced PHE mineralization by P. strain R. The enhancement of PHE mineralization could not be explained by P. aeruginosa-mediated PHE degradation. The addition of rhamnolipid at concentrations above the critical micelle concentration (CMC) resulted in enhanced PHE release from test soils. These results suggest that the PHE-degrading strains were able to access different pools of PHE and that the biosurfactant-enhanced release of PHE from soils did not result in enhanced biodegradation. The results also demonstrated that bacteria with the catabolic potential to degrade sorbed hydrophobic contaminants could interact commensally with surfactant-producing strains by an unknown mechanism to hasten the biodegradation of aromatic hydrocarbons. Thus, understanding interactions among microbes may provide opportunities to further enhance biodegradation of soil-bound organic contaminants.

The prevalence of multiple sclerosis in Tayside, Scotland: do latitudinal gradients really exist?

To determine the prevalence of multiple sclerosis (MS) in the Tayside Health Board Area, Scotland, we carried out a population-based survey using four intersecting sources (Neurology Department records, a survey of general practitioners, Scottish Morbidity Records of discharges from hospitals and visual evoked response requests). A two-source capture-recapture model estimated survey coverage, and direct age-sex standardisation was used to take account of different population structures. Comparisons were made between the prevalence in Scotland and that in the rest of the United Kingdom. A total of 727 (definite and probable) and 880 cases (early, probable and possible) were identified using the criteria of Poser et al. and those of Allison and Millar in a population of 395,600 (1995 mid-year estimate). The prevalence of MS on 1 September 1996 was 184/100,000 (95% confidence interval 171-198) and 222/100,000 (95% confidence interval 210-240), respectively. The two-source capture-recapture model estimated that the survey was between 93% and 99% complete. Age-sex standardisation eliminated certain north-south differences in prevalence when comparisons were made with previous surveys. Diagnostic misclassification may also have influenced reported prevalence statistics. The prevalence is similar to that found in revised figures from the Grampian region in Scotland but significantly higher than recent estimates from England and Wales. Methodological differences may account for most of the reported differences between north and south, although there is still evidence to suggest that MS is more prevalent in northern Great Britain and Northern Ireland than in England and Wales.