Molecular identification of streptomycin monoresistant Mycobacterium tuberculosis related to multidrug-resistant W strain.

A distinct branch of the Mycobacterium tuberculosis W phylogenetic lineage (W14 group) has been identified and characterized by various genotyping techniques. The W14 group comprises three strain variants: W14, W23, and W26, which accounted for 26 clinical isolates from the New York City metropolitan area. The W14 group shares a unique IS6110 hybridizing banding motif as well as distinct polymorphic GC-rich repetitive sequence and variable number tandem repeat patterns. All W14 group members have high levels of streptomycin resistance. When the streptomycin resistance rpsL target gene was sequenced, all members of this strain family had an identical mutation in codon 43. Patients infected with the W14 group were primarily of non- Hispanic black origin (77%); all were US-born. Including HIV positivity, 84% of the patients had at least one known risk factor for tuberculosis

Alkaline igneous rocks of the Kola Peninsula: potential source rocks for abiogenic hydrocarbons via Fischer-Tropsch type reactions

The Kola alkaline province of NW Russia is the type example of the occurrence of abiogenic hydrocarbons (HCs) in crystalline rocks. Methane and higher hydrocarbons, up to C5H12, are contained primarily within abundant fluid inclusions in rock-forming minerals or as free gas contained in sealed microfractures or along grain boundaries. Such occurrences are not unique to Kola. High-temperature, hydrocarbon-rich fluid inclusions are present in alkaline rocks from Ilimaussaq, Greenland, and in recent years they have been described in other silica-undersaturated igneous rocks as well as in hydrothermal systems associated with basic igneous rocks. Two main models (Potter and Konnerup-Madsen, 2003) have been proposed for the genesis of these abiogenic HCs: (1) a late-magmatic model whereby the HCs are equilibrium products of volatiles exsolved directly from magmas, and; (2) a post-magmatic, disequilibrium model whereby HCs are generated via Fischer-Tropsch type reactions at ca. 350°C involving CO2 and H2O bearing fluids, linked to redox reactions accompanying hydrothermal alteration. This paper reports on recent and current research on the origin and distribution of HCs from the Khibina and Lovozero intrusions of the Kola Peninsular that supports an abiogenic origin through Fischer- Tropsch synthesis. An approximate estimate of the total volume of HCs contained within these rocks can be made on the assumption that CH4-rich inclusions, with a mean density of 0.1 g/cc occupy 0.1% on the total rock volume. For a body of rock 20 x 10km (less than 10% of the area of the Khibina and Lovozero intrusions) and 1km thickness this corresponds to some 40 million tonnes of methane and associated higher HCs. Due to the low permeability these complexes cannot yet be considered as potentially economic. However, large volumes of free-flowing methane have been recorded as being released when rocks are fractured as a result of drilling during underground mining (Nivin et al., 2001) suggesting the ease with which sealed microfractures and fluid inclusions planes may be opened up and connected. Hence they are potential source rocks for abiogenic HCs especially in areas where there has been major faulting and accompanying hydrothermal alteration. Where these faults extended to sufficient depth to intersect suitable conditions for Fischer-Tropsch reactions they would have acted as focal points for HC generation as well as having acted as suitable pathways for their migration to potential traps at higher levels in the crust. Modern day reactivation of these fault systems, by either natural or anthropogenic processes will cause the release of significant amounts of methane and higher HCs trapped on grain boundaries and in secondary fluid inclusions

Radiogenic helium isotope fractionation: the role of tritium as 3He precursor in geochemical applications

Reduced 4He/3He ratios, e.g., down to ≈1/100 times those expected from radiogenic production, were observed in sedimentary rocks. Formation and history of these rocks eliminate a contribution of mantle 3He-bearing fluid. To explain the difference between the observed and the calculated production 4He/3He ratios Loosli et al. (1995) and Tolstikhin et al. (1996) suggested a different behaviour of helium and tritium in damage tracks produced by emission of these nuclides. Generally, the tracks cross grain boundaries or some imperfections within a rock or mineral allowing a fast loss of noble 4He and 3He atoms. However, radiogenic 3He has the precursor 3H, generated in the exothermic 6Li(nt, α)3H + 4.5 MeV reaction. The energetic tritons produce damage tracks comparable with those from α-decay of U and Th series. If 3H is chemically bound within a track, and the track is able to recover via some diagenetic process before the 3H decay, then 3H and daughter 3He atoms are trapped within the recovered track. This mechanism would explain the shorter residence time of 4He in the rocks/minerals than of 3He; therefore, 4He/3He ratios could decrease through time. To check this mechanism 4He, 3H, and 3He (from 3H-decay) were produced by the above reaction in special targets, consisting of layered composites of thin sections of quartz, sample, Li-bearing cover, sample, and quartz. The samples were the same rocks in which reduced 4He/3He ratios have been previously observed. Each target was placed in a quartz ampoule, which was then pumped out, sealed off, and then exposed to the flux of thermal neutrons in a reactor. After irradiation and cooling down (total duration 145 days), the nuclides produced during (3H, 3He, 4He) and after (3He) irradiation were measured in the gas phase above the targets and compared with their total quantities expected from the Li abundance and the integrated neutron flux. The ratios obtained were 3H(gas)/3H(total) < 0.05 and 3He(gas)/3He(total) varying from 0.2 to 0.9. The average residence times τ of 3H and 3He, respectively, were estimated to be ≈16 and ≈0.25 yr for this first time interval, which included the irradiation of the targets. After these first measurements, the targets were kept in a vacuum system under room temperature for 210 days and the amounts of 3H and 3He, which accumulated above the targets during this second time interval under fully controlled conditions, were also measured. Much slower rates of gas loss from the same targets with average residence times of τ(3H) ≈ 600 yr and τ(He) ≈ 1.6 yr resulted for this second time interval. Probably these longer residence times are closer to those in the relevant natural environments, the 3H residence time being much longer than the 3H half-life. In all cases the inequality τ(3He) ≪ τ(3H) is valid. This confirms the proposed scenario envisaging longer retention of 3H than He in damage tracks. Within the frame of this scenario the life-time of 3H gives a time constraint on diagenetic processes; at least one to several newly formed atomic layers should appear during ∼10 yr to recover the tracks