No abstract

Seasonal variation in P sedimentation, sediment P release, and sediment P pools was studied in a coastal marine sediment at 16-m water depth. Net sedimentation of P amounted to 5 l-63 mmol m-2 yr-l, compared to a sediment P release of 34 mmol m-2 yr-l. The resulting deficit corresponded with a burial flux of 18 mmol P m-2 yr-I. Iron-bound P was the most dynamic P pool in the mixed surface sediment, where it made up 175 mmol m-2 of a total of 530 mmol P m-2. Iron-bound P decreased rapidly with depth and contributed only 3.5% to the burial flux. P sedimented in spring was retained in the pool of iron-bound P until SeptemberOctober, when half of the annual P release occurred. The autumn maximum in P release seemed to be linked to sulfate reduction by two mechanisms: sulfide was primarily responsible for the reduction of ferric oxyhydroxides (FeOOH) and hence the release of iron-bound P, and precipitation of FeS and FeS, restricted the upward migration of Fe 2+ but not of dissolved reactive phosphate (DRP) and resulted in a saturation of sorption sites for DRP on FeOOH in the sediment surface layer. The saturation of sorption sites was reflected by a minimum ratio of FeOOH to iron-bound P in surface sediment measured in October. Seasonal changes in this ratio provided the best correlation with the DRP efflux (R = -0.74), indicating that adsorption onto FeOOH is probably the most important factor controlling sediment P release.

Tuberculosis patients may harbor both drug-susceptible and -resistant bacteria, i.e., heteroresistance. We used mixtures of rifampin-resistant and -susceptible Mycobacterium tuberculosis strains to simulate heteroresistance in patient samples. Molecular tests can be used for earlier discovery of multidrug resistance (MDR), but the sensitivity to detect heteroresistance is unknown. Conventional phenotypic drug susceptibility testing was the most sensitive, whereas two line probe assays and sequencing were unable to detect the clinically important 1% resistant bacteria. Patients with tuberculosis (TB) that harbor drug-susceptible Mycobacterium tuberculosis strains may also have a small proportion of drug-resistant bacteria that develops spontaneously during replication, normally at a rate of 10 Ϫ8 to 10 Ϫ9 mutations/ cell division (1). For rifampin (Rif) resistance, mutations are almost exclusively found in a single gene, rpoB (2). Conventional drug susceptibility testing (DST) aims to determine if 1% or more of the bacterial population in clinical specimens is drug resistant (3, 4). In this study, cultures that contain both susceptible and at least 1% resistant bacteria are defined as heteroresistant. Heteroresistance is thought to be an early stage in the development of drug-resistant TB in a patient. In such cases, failing to detect resistance may lead to insufficient treatment and treatment failure. As a consequence, spread of resistant bacteria may occur in the future (5). The prevalence of heteroresistance is unknown and is presumably dependent on the local resistance epidemiology. Findings of heteroresistance are accidental, and simple methods for the detection are needed (6).In recent years, a number of genotypic methods have become available for rapid detection of mutations that may confer resistance. Molecular tests have been recommended for use worldwide, with the objective of earlier discovery of multidrug resistance (MDR) (http://www.who.int/tb/features_archive/policy _statement.pdf). These assays are important for the global scaling up of detection of MDR-TB. However, little is known of the sensitivity of these methods to detect resistance in heteroresistant specimens. The aim of the present study was to evaluate the ability of different DST methods to detect Rif resistance when heteroresistance is present.Two freeze-dried strains each of the spoligo families Haarlem and Beijing were obtained from the WHO Tropical Disease Research (TDR) TB Strain Bank. The Haarlem strain TB-TDR-063 was susceptible, and TB-TDR-165 was Rif resistant with the rpoB H526Y mutation. The Beijing strain TB-TDR-077 was susceptible, and TB-TDR-068 was Rif resistant with the rpoB S531L mutation. The susceptible strains from both families had wild-type (WT) DNA in rpoB. The strains were subcultured in Dubos with 0.045% Tween 80 (SSI Diagnostika, Hilleroed, Denmark) with 1 mg/ml Rif (BD, Franklin Lakes, NJ) diluted in water for the resistant strains. After 2 weeks of incubation at 37°C, the bacterial concentrations in liquid medi...

The "Beijing" Mycobacterium tuberculosis (Mtb) lineage 2 (L2) is spreading globally and has been associated with accelerated disease progression and increased antibiotic resistance. Here we performed a phylodynamic reconstruction of one of the L2 sublineages, the central Asian clade (CAC), which has recently spread to western Europe. We find that recent historical events have contributed to the evolution and dispersal of the CAC. Our timing estimates indicate that the clade was likely introduced to Afghanistan during the 1979-1989 Soviet-Afghan war and spread further after population displacement in the wake of the American invasion in 2001. We also find that drug resistance mutations accumulated on a massive scale in Mtb isolates from former Soviet republics after the fall of the Soviet Union, a pattern that was not observed in CAC isolates from Afghanistan. Our results underscore the detrimental effects of political instability and population displacement on tuberculosis control and demonstrate the power of phylodynamic methods in exploring bacterial evolution in space and time.

The finescale structure and evolution of a cold front in the presence of small-scale circulations are examined using overdetermined dual-Doppler syntheses of mobile radar data along with thermodynamic data and cloud imagery collected on 10 June 2002 during the International H2O Project (IHOP). Linear clear-air reflectivity maxima and open cellular convection intersect the cold front, causing spatial variations in convergence along the front. Small-scale vertical vorticity maxima (misocyclones) often are coincident with these intersections and are associated with vertical velocity maxima. Throughout the deployment, trajectory analyses indicate that parcels entering the frontal circulation travel predominately in the along-front direction. During the first hour of the deployment, upward motion is nearly continuous along the front. Consequently, parcels remain in regions of upward motion as they move along the front, and many eventually ascend to cloud base. In response, a line of cumulus clouds develops along the front. Later in the deployment, however, enhanced warming behind the cold front causes the frontal circulation to weaken. Small-scale features such as misocyclones play a larger role in organizing upward motion along the front than when the front was stronger. Misocyclones contort the weakened cold front and are associated with kinks in radar reflectivity and fractures in upward motion. Parcels moving along the front now experience regions of both upward and downward forcing due to this fracturing. Hence, many of these parcels do not retain upward motion long enough to reach cloud base, and clouds along the cold front dissipate in the dry air above the boundary layer. Parcels that remain coincident with upward motion maxima, such as those maxima associated with misocyclones, however, often still reach the top of the radar domain and presumably cloud base.

Haploid cells of the fission yeast Schizosaccharomyces pombe exist in one of two mating types, referred to as M and P. Conjugation occurs between cells of opposite mating type and is controlled by the reciprocal action of diffusible pheromones. Loss of function of the sxa2 gene in M cells causes hypersensitivity to the P-factor mating pheromone and a reduction in mating efficiency. Here we demonstrate the secretion of an sxa2-dependent carboxypeptidase that inactivates P-factor by removal of the C-terminal leucine residue.

Mycobacterium chimaera was present at high rates (>80%) in heater–cooler units (HCUs) from all 5 thoracic surgery departments in Denmark. Isolates were clonal to HCU-associated isolates from the United States (including some from patients) and United Kingdom. However, M. chimaera from 2 brands of HCU were genetically distinct.

Patients may harbor both drug-susceptible and -resistant bacteria, representing heteroresistance. We studied mixtures of isoniazid-resistant and -susceptible Mycobacterium tuberculosis strains. Conventional drug susceptibility testing was the most sensitive method of detection, whereas the line probe assay and sequencing were not able to detect the clinically relevant 1% proportion of resistant bacteria. Patients with tuberculosis (TB) usually harbor susceptible Mycobacterium tuberculosis but may also have a small proportion of drug-resistant isogenic variants that develop spontaneously during replication. For isoniazid (Inh) resistance, mutations are introduced at rates of approximately 1 mutation per 10 8 to 10 10 divisions (1). The mutations are found in several genes but mainly in the katG gene and in the inhA promoter (2). An increased proportion of resistant variants in a susceptible main population of isogenic or nonisogenic bacteria is called "heteroresistance" in this paper. Standard short-course chemotherapy with combinations of several drugs prevents the selection of drug-resistant bacteria during treatment. The proportion of patients infected with heteroresistant tuberculosis is largely unknown. In the 1960s, the criteria for defining clinically relevant drug resistance were set from clinical and bacteriological studies. By consensus, a cutoff of 1% for Inh was decided. This is the proportion of resistant bacteria above which therapeutic success had been demonstrated to be unlikely (3, 4). Therefore, phenotypic drug susceptibility testing (DST) aims to determine if 1% or more of the bacterial population in clinical specimens is drug resistant.In recent years, commercial genotypic methods have become available for detection of mutations that may confer resistance. Among these, it is only with the line probe assay (LPA) GenoType MTBDRplus that resistance to Inh can be detected by analysis of the katG and inhA genes (5). The LPA uses PCR covering areas where mutations associated with resistance are common. It is followed by hybridization of target sequences to a membrane strip; the hybrids are visualized as bands. The test detects specific mutations as well as unspecified mutations, the latter by the absence of at least one wild-type band.In June 2008, a WHO Expert Consultation concluded that sufficient information was available to recommend the use of LPAs for detection of multidrug resistance (MDR) in M. tuberculosis isolates and smear-positive sputum specimens (http://www.who .int/tb/features_archive/policy_statement.pdf). The newly published European Union Standards for Tuberculosis Care recommends also that rapid testing for Inh and rifampin should be performed on primary specimens when MDR TB is suspected (6).These assays are important for the global scaling up of detection of MDR and extensively drug-resistant (XDR) M. tuberculosis. However, little is known of the sensitivity of these methods for detection of small proportions of drug-resistant bacteria. Furthermore, to facilitate the DSTs, labor...