Specific growth rate plays a critical role in hydrogen peroxide resistance of the marine oligotrophic ultramicrobacterium Sphingomonas alaskensis strain RB2256

The marine oligotrophic ultramicrobacterium Sphingomonas alaskensis RB2256 has a physiology that is distinctly different from that of typical copiotrophic marine bacteria, such as Vibrio angustum S14. This includes a high level of inherent stress resistance and the absence of starvation-induced stress resistance to hydrogen peroxide. In addition to periods of starvation in the ocean, slow nutrient-limited growth is likely to be encountered by oligotrophic bacteria for substantial periods of time. In this study we examined the effects of growth rate on the resistance of S. alaskensis RB2256 to hydrogen peroxide under carbon or nitrogen limitation conditions in nutrient-limited chemostats. Glucose-limited cultures of S. alaskensis RB2256 at a specific growth rate of 0.02 to 0.13 h(-1) exhibited 10,000-fold-greater viability following 60 min of exposure to 25 mM hydrogen peroxide than tells growing at a rate of 0.14 h(-1) or higher. Growth rate control of stress resistance was found to be specific to carbon and energy limitation in this organism. In contrast, V. angustum S14 did not exhibit growth rate-dependent stress resistance. The dramatic switch in stress resistance that was observed under carbon and energy limitation conditions has not been described previously in bacteria and thus may be a characteristic of the oligotrophic ultramicrobacterium, Catalase activity varied marginally and did not correlate with the growth rate, indicating that hydrogen peroxide breakdown was not the primary mechanism of resistance. More than 1,000 spots were resolved on silver-stained protein gels for cultures growing at rates of 0.026, 0.076, and 0.18 h(-1). Twelve protein spots had intensities that varied by more than twofold between growth rates and hence are likely to be important for growth rate-dependent stress resistance. These studies demonstrated the crucial role that nutrient limitation plays in the physiology of S. alaskensis RB2256, especially under oxidative stress conditions.

Twenty-eight divergent polysaccharide loci specifying within and amongst strain capsule diversity in three strains of Bacteroides fragilis

Comparison of the complete genome sequence of Bacteroides fragilis 638R, originally isolated in the USA, was made with two previously sequenced strains isolated in the UK (NCTC 9343) and Japan (YCH46). The presence of 10 loci containing genes associated with polysaccharide (PS) biosynthesis, each including a putative Wzx flippase and Wzy polymerase, was confirmed in all three strains, despite a lack of cross-reactivity between NCTC 9343 and 638R surface PS-specific antibodies by immunolabelling and microscopy. Genomic comparisons revealed an exceptional level of PS biosynthesis locus diversity. Of the 10 divergent PS-associated loci apparent in each strain, none is similar between NCTC 9343 and 638R. YCH46 shares one locus with NCTC 9343, confirmed by mAb labelling, and a second different locus with 638R, making a total of 28 divergent PS biosynthesis loci amongst the three strains. The lack of expression of the phase-variable large capsule (LC) in strain 638R, observed in NCTC 9343, is likely to be due to a point mutation that generates a stop codon within a putative initiating glycosyltransferase, necessary for the expression of the LC in NCTC 9343. Other major sequence differences were observed to arise from different numbers and variety of inserted extra-chromosomal elements, in particular prophages. Extensive horizontal gene transfer has occurred within these strains, despite the presence of a significant number of divergent DNA restriction and modification systems that act to prevent acquisition of foreign DNA. The level of amongst-strain diversity in PS biosynthesis loci is unprecedented.

The effect of temperature and strain rate on the deformation behaviour, structure development and properties of biaxially stretched PET-clay nanocomposites.

The inclusion of a synthetic fluoromica clay in PET affects its processability via biaxial stretching and stretching temperature (95 °C and 102 °C) and strain rate (1 s-1 and 2 s-1) influence the structuring and properties of the stretched material. The inclusion of clay has little effect on the temperature operating window for the PET–clay but it has a major effect on deformation behaviour which will necessitate the use of much higher forming forces during processing. The strain hardening behaviour of both the filled and unfilled materials is well correlated with tensile strength and tensile modulus. Increasing the stretching temperature to reduce stretching forces has a detrimental effect on clay exfoliation, mechanical and O2 barrier properties. Increasing strain rate has a lesser effect on the strain hardening behaviour of the PET–clay compared with the pure PET and this is attributed to possible adiabatic heating in the PET–clay sample at the higher strain rate. The Halpin–Tsai model is shown to accurately predict the modulus enhancement of the PET–clay materials when a modified particle modulus rather than nominal clay modulus is used.

Complete Genome Sequence of Propionibacterium acnes Type IB Strain 6609

Propionibacterium acnes is an anaerobic Gram-positive bacterium that forms part of the normal human cutaneous microbiota and is thought to play a central role in acne vulgaris, a chronic inflammatory disease of the pilosebaceous unit (I. Kurokawa et al., Exp. Dermatol. 18:821-832, 2009). Here we present the whole genome sequence of P. acnes type IB strain 6609, which was recovered from a skin sample from a woman with no recorded acne history and is thus considered a nonpathogenic strain (I. Nagy, Microbes Infect. 8:2195-2205, 2006).