Mathematical Modelling of Mycobacterium tuberculosis VNTR Loci Estimates a Very Slow Mutation Rate for the Repeats

Minisatellites are highly variable tandem repeats used for over 20 years in humans for DNA fingerprinting. In prokaryotes fingerprinting techniques exploiting VNTR (variable number of tandem repeats) polymorphisms have become widely used recently in bacterial typing. However although many investigations into the mechanisms underlying minisatellite variation in humans have been performed, relatively little is known about the processes that mediate bacterial minisatellite polymorphism. An understanding of this is important since it will influence how the results from VNTR experiments are interpreted. The minisatellites of Mycobacterium tuberculosis are well characterized since they are some of the few polymorphic loci in what is otherwise a very homogeneous organism. Using VNTR results from a well-defined and characterized set of M. tuberculosis strains we show that the repeats at a locus are likely to evolve by stepwise contraction or expansion in the number of repeats. A stochastic continuous-time population mathematical model was developed to simulate the evolution of the repeats. This allowed estimation of the tendency of the repeats to increase or decrease and the rate at which they change. The majority of loci tend to lose rather than gain repeats. All of the loci mutate extremely slowly, with an average rate of 2.3 x 10(-8), which is 350 times slower than that of a set of VNTR repeats with similar diversity observed experimentally in Escherichia coli. This suggests that the VNTR profile of a strain of M. tuberculosis will be indicative of its clonal lineage and will be unlikely to vary in epidemiologically-related strains.     

Effects of drill cuttings on biogeochemical fluxes and macrobenthos of marine sediments

Experimental work was performed on drill cuttings sampled from off-shore drilling operations. The cuttings contained remnants of two different types of drilling muds: a water-ilmenite based mud and an olefin-barite based mud. In a pilot experiment, a gradient of up to 65 mm thick layers of water-ilmenite based cuttings were added to 78 cm² core samples. In another set-up, 3 mm layers of water-ilmenite and olefin-barite based cuttings were added to replicate 1000 cm² box-core samples with natural benthic communities transferred from the Oslofjord, S.E. Norway. Boxes with no addition and addition of 3 mm “clean” sediment were used for control. Increased consumption of oxygen and nitrate indicated the presence of degradable organic phases in both mud systems. The release of silicate showed a general decrease with increasing thickness of the cuttings layer, but maximum rates in the 3.1 mm treatment indicated increased bioturbation at low and moderate doses. The initial (field) composition of the macrobenthic communities was maintained throughout the 3 months experimental period, and at community level, no significant difference was observed between the four treatments at the end of the exposure period. However, after grouping the treatments into “clean” (untreated control and 3 mm clean sediment) and “cuttings” (3 mm water-ilmenite and 3 mm olefin-barite based cuttings), multivariate statistical analyses revealed a significant difference in community composition between clean and cuttings treatments, and three taxa showed significantly reduced abundances in the cuttings treatments. Chemical toxicity of mud components is assumed to be small, and the observed effect was more likely a result of physical properties such as the size or shape of cuttings particles.     

Melanoma cell sensitivity to Docetaxel-induced apoptosis is determined by class III beta-tubulin levels

We have previously shown that Docetaxel-induced variable degrees of apoptosis in melanoma. In this report, we studied the beta-tubulin repertoire of melanoma cell lines and show that class III beta-tubulin expression correlated with Docetaxel-resistance. Sensitive cells showed low levels of class III beta-tubulin with little microtubular incorporation, whereas class III beta-tubulin expression was higher in resistant cells and was incorporated into the cytoskeleton. As proof of concept, abrogation of class III by siRNA reverted Docetaxel-resistant cells to a sensitive phenotype, restoring the microtubular polymerisation response and promoting high levels of apoptosis through Bax activation. These results suggest that phenotypic expression of beta-tubulin class III in melanoma may help identify patients with melanoma that can respond to taxanes.     

Invasive entamoebae in pronghorn (Antilocapra americana) from Wyoming

Trophozoites and cysts of an amoeba resembling Entamoeba bovis were recovered from soft stools of captive pronghorn fawns (Antilocapra americana). Chronic or intermittent diarrhea was observed in most individuals in two groups of hand-raised 1- to 8-mo-old pronghorns. Ileocecal lymph nodes were mildly to moderately enlarged. Microscopic lesions were characterized by lymphoid hyperplasia, focal necrosis and pyogranulomatous inflammation in lymph nodes and focal necrosis and diffuse nonsuppurative enteritis in ileum and cecum. In 12 of 17 fawns, trophic stages of amoebae were observed in the submucosa of the cecum and/or the cortex of the ileocecal lymph node. This is the first report of E. bovis-like organisms invading and causing pathological changes in the tissues of their host.