Molecular analysis of region 1 of the Escherichia coli K5 antigen gene cluster: a region encoding proteins involved in cell surface expression of capsular polysaccharide.

The nucleotide sequence of region 1 of the K5 antigen gene cluster of Escherichia coli was determined. This region is postulated to encode functions which, at least in part, participate in translocation of polysaccharide across the periplasmic space and onto the cell surface. Analysis of the nucleotide sequence revealed five genes that encode proteins with predicted molecular masses of 75.7, 60.5, 44, 43, and 27 kDa. The 27-kDa protein was 70.7% homologous to the CMP-2-keto-3-deoxyoctulosonic acid synthetase enzyme encoded by the E. coli kdsB gene, indicating the presence of a structural gene for a similar enzyme within the region 1 operon. The 43-kDa protein was homologous to both the Ctrb and BexC proteins encoded by the Neisseria meningitidis and Haemophilus influenzae capsule gene clusters, respectively, indicating common stages in the expression of capsules in these gram-negative bacteria. However, no homology was detected between the 75.7, 60.5-, and 44-kDa proteins and any of the proteins so far described for the H. influenzae and N. meningitidis capsule gene clusters.     

Expression of the Escherichia coli K5 capsular antigen: immunoelectron microscopic and biochemical studies with recombinant E. coli.

The capsular K5 polysaccharide, a representative of group II capsular antigens of Escherichia coli, has been cloned previously, and three gene regions responsible for polymerization and surface expression have been defined (I. S. Roberts, R. Mountford, R. Hodge, K. B. Jann, and G. J. Boulnois, J. Bacteriol. 170:1305-1310, 1988). In this report, we describe the immunoelectron microscopic analysis of recombinant bacteria expressing the K5 antigen and of mutants defective in either region 1 or region 3 gene functions, as well as the biochemical analysis of the K5 capsular polysaccharide. Whereas the K5 clone expressed the K5 polysaccharide as a well-developed capsule in about 25% of its population, no capsule was observed in whole mount preparations and ultrathin sections of the expression mutants. Immunogold labeling of sections from the region 3 mutant revealed the capsular K5 polysaccharide in the cytoplasm. With the region 1 mutant, the capsular polysaccharide appeared associated with the cell membrane, and, unlike the region 3 mutant polysaccharide, the capsular polysaccharide could be detected in the periplasm after plasmolysis of the bacteria. Polysaccharides were isolated from the homogenized mutants with cetyltrimethylammonium bromide. The polysaccharide from the region 1 mutant had the same size as that isolated from the capsule of the original K5 clone, and both polysaccharides were substituted with phosphatidic acid. The polysaccharide from the region 3 mutant was smaller and was not substituted with phosphatidic acid. These results prompt us to postulate that gene region 3 products are involved in the translocation of the capsular polysaccharide across the cytoplasmic membrane and that region 1 directs the transport of the lipid-substituted capsular polysaccharide through the periplasm and across the outer membrane.     

Analysis of genes coding for the sialic acid-binding adhesin and two other minor fimbrial subunits of the S-fimbrial adhesin determinant of Escherichia coli

The S fimbrial adhesin (Sfa) enables Escherichia coli to attach to sialic acid-containing receptor molecules of eukaryotic cells. As previously reported, the genetic determinant coding for the Sfa of an E. coli O6 strain was cloned, the gene coding for the major fimbrial subunit was identified and sequenced and the S specific adhesin was detected. Here we present evidence that in addition to the major subunit protein SfaA three other minor subunit proteins, SfaG (17 kD), SfaS (14 kD) and SfaH (31 kD) can be isolated from the S-specific fimbrial adhesin complex. The genes coding for these minor subunits were identified, mutagenized separately and sequenced. Using haemagglutination tests, electron-microscopy and quantitative ELISA assays with monoclonal anti-SfaA and anti-SfaS antibodies the functions of the minor subunits were determined. It was determined that SfaS is identical to the S-specific adhesin, which also plays a role in determination of the degree of fimbriation of the cell. The minor subunit SfaH also had some influence on the level of fimbriation of the cell, while SfaG is necessary for full expression of S-specific binding. It was further shown that the amino-terminal protein sequence of the isolated SfaS protein was identical to the protein sequence calculated from the DNA sequence of the sfaS gene locus.     

Spatial analysis of Tasmania’s native vegetation cover and potential implications for biodiversity conservation

Summary The landscape modification model proposed by McIntyre and Hobbs (1999) was used to assess the modification of Tasmania’s native vegetation and its potential implications for biodiversity conservation. The inclusion of new ‘substates’ in the model allowed the varying degrees of landscape variegation and fragmentation observed in Tasmania to be quantified. The mapped extent of Tasmania’s native vegetation is approximately 5.06 million ha or 74% of the land area. The extent of native vegetation varies across bioregions from a low of around 36% in the Tasmanian Northern Midlands bioregion to a high of 94% in the Tasmanian West bioregion. Overall, the Tasmanian landscape can be described as medium variegated as the State retains 76% cover of native vegetation, by area. Two of Tasmania’s nine bioregions are in an intact state, four are variegated, and three are fragmented. Seven of the State’s 48 catchments are in an intact state, 24 catchments are variegated, and 17 are fragmented. Tasmania was estimated to support 33 760 patches of native vegetation. Fewer than 3% of these patches exceed 50 ha in area. Small and medium patches occur predominantly on freehold land with grazing as a major land use, whereas large patches occur predominantly on crown land with conservation and production forestry as the major land uses. One feature of the State’s native vegetation is the large tract of native vegetation ecosystems in western Tasmania. Opportunities arise to sustain the resilience of these native ecosystems both by consolidating the formal protection of vegetation within catchments such as the Arthur and Pieman and by strengthening environmental management in adjacent areas. Bioregions and catchments where climate change may be of particular concern for biodiversity conservation and management include the Tasmanian Northern Midlands bioregion and Cam catchment in north‐western Tasmania. The maintenance and enhancement of patches of remnant vegetation in these areas will be challenging and appears likely to require strategic, multiscale and coordinated natural resource management over decades. Limiting the loss of native vegetation across the entire range of landscape states in Tasmania appears essential to mitigate the further decline of biodiversity.     

How the Black Grouse was lost: historic reconstruction of its status and distribution in Lower Saxony (Germany)

In the Central European lowlands, the Black Grouse (Tetrao tetrix) is restricted to isolated remnant populations. Status reports have been published for some of them, but comparative analyses of Black Grouse dynamics across larger parts of the Central European range are missing. In this paper, we used published and unpublished historic information on local occurrences of Black Grouse in 37,000 km² of the German federal state of Lower Saxony to reconstruct changes in the species’ distribution and abundance since the 1950s. We calculated population trends over 52 years (1955–2006) using software trends and indices in monitoring data (TRIM). Results showed two phases: an initial crash phase (1950s–1980s) when many local populations went extinct, and a recovery phase (1990s–2000s) for the remnants of the initial distribution. Differences in timing and extent of the crash were related at habitat type. Our study indicates that reconstructing population trends and distributions across larger geographic areas from historic data may enable comparative analyses of drivers of population dynamics across sites, and thus contribute to a better understanding of the causes of Black Grouse decline.     

Genetic diversity,introgression and relationships among West/Central African cattle breeds

Genetic diversity, introgression and relationships were studied in 521 individuals from 9 African Bos indicus and 3 Bos taurus cattle breeds in Cameroon and Nigeria using genotype information on 28 markers (16 microsatellite, 7 milk protein and 5 blood protein markers). The genotypes of 13 of the 16 microsatellite markers studied on three European (German Angus, German Simmental and German Yellow) and two Indian (Nelore and Ongole) breeds were used to assess the relationships between them and the African breeds. Diversity levels at microsatellite loci were higher in the zebu than in the taurine breeds and were generally similar for protein loci in the breeds in each group. Microsatellite allelic distribution displayed groups of alleles specific to the Indian zebu, African taurine and European taurine. The level of the Indian zebu genetic admixture proportions in the African zebus was higher than the African taurine and European taurine admixture proportions, and ranged from 58.1% to 74.0%. The African taurine breed, Muturu was free of Indian zebu genes while its counter Namchi was highly introgressed (30.2%). Phylogenic reconstruction and principal component analysis indicate close relationships among the zebu breeds in Cameroon and Nigeria and a large genetic divergence between the main cattle groups – African taurine, European taurine and Indian zebu, and a central position for the African zebus. The study presents the first comprehensive information on the hybrid composition of the individual cattle breeds of Cameroon and Nigeria and the genetic relationships existing among them and other breeds outside of Africa. Strong evidence supporting separate domestication events for the Bos species is also provided.     

Geographic distribution of haplotype diversity at the bovine casein locus

The genetic diversity of the casein locus in cattle was studied on the basis of haplotype analysis. Consideration of recently described genetic variants of the casein genes which to date have not been the subject of diversity studies, allowed the identification of new haplotypes. Genotyping of 30 cattle breeds from four continents revealed a geographically associated distribution of haplotypes, mainly defined by frequencies of alleles at CSN1S1 and CSN3. The genetic diversity within taurine breeds in Europe was found to decrease significantly from the south to the north and from the east to the west. Such geographic patterns of cattle genetic variation at the casein locus may be a result of the domestication process of modern cattle as well as geographically differentiated natural or artificial selection. The comparison of African Bos taurus and Bos indicus breeds allowed the identification of several Bos indicus specific haplotypes (CSN1S1*C-CSN2*A²-CSN3*A_I/CSN3*H) that are not found in pure taurine breeds. The occurrence of such haplotypes in southern European breeds also suggests that an introgression of indicine genes into taurine breeds could have contributed to the distribution of the genetic variation observed.     

Maximal rowing has an acute effect on the blood-gas barrier in elite athletes.

The purpose of the study was to evaluate the effects of maximal exercise on the integrity of the alveolar epithelial membrane using the clearance rate of aerosolized 99mTc-labeled diethylenetriaminepentaacetic acid as an index for the permeability of the lung blood-gas barrier. Ten elite rowers (24.3 +/- 4.6 yr of age) completed two 20-min pulmonary clearance measurements immediately after and 2 h after 6 min of all-out rowing (initial and late, respectively). All subjects participated in resting control measurements on a separate day. For each 20-min measurement, lung clearance was calculated for 0-7 and 10-20 min. Furthermore, scintigrams were processed from the initial and late measurements of diethylenetriaminepentaacetic acid clearance. Compared with control levels, the pulmonary clearance measurement after rowing was increased from 1.2 +/- 0.5 to 2.4 +/- 1.0%/min (SD) at 0-7 min (P < 0.01) and from 0.8 +/- 0.3 to 1.5 +/- 0.4%/min at 10-20 min (P < 0.0005), returning to resting levels within 2 h. In 6 of 10 subjects, ventilation distribution on the lung scintigrams was inhomogeneous at the initial measurement. The study demonstrates an acute increased pulmonary clearance after maximal rowing. The ventilation defects identified on the lung scintigrams may represent transient interstitial edema secondary to increased blood-gas barrier permeability induced by mechanical stress.     

Validation of Network Communicability Metrics for the Analysis of Brain Structural Networks

Computational network analysis provides new methods to analyze the brain''s structural organization based on diffusion imaging tractography data. Networks are characterized by global and local metrics that have recently given promising insights into diagnosis and the further understanding of psychiatric and neurologic disorders. Most of these metrics are based on the idea that information in a network flows along the shortest paths. In contrast to this notion, communicability is a broader measure of connectivity which assumes that information could flow along all possible paths between two nodes. In our work, the features of network metrics related to communicability were explored for the first time in the healthy structural brain network. In addition, the sensitivity of such metrics was analysed using simulated lesions to specific nodes and network connections. Results showed advantages of communicability over conventional metrics in detecting densely connected nodes as well as subsets of nodes vulnerable to lesions. In addition, communicability centrality was shown to be widely affected by the lesions and the changes were negatively correlated with the distance from lesion site. In summary, our analysis suggests that communicability metrics that may provide an insight into the integrative properties of the structural brain network and that these metrics may be useful for the analysis of brain networks in the presence of lesions. Nevertheless, the interpretation of communicability is not straightforward; hence these metrics should be used as a supplement to the more standard connectivity network metrics.