Heterogeneous responses to ozone and nitrogen alter the species composition of Mediterranean annual pastures.

Air pollution represents a threat to biodiversity throughout the world and particularly in the Mediterranean area, where high tropospheric ozone (O3) concentrations and atmospheric nitrogen (N) deposition are frequently recorded. Mediterranean annual pastures are among the most important ecosystems in southern Europe due to their high biodiversity and extension. Aiming to study the responses of these communities to the main atmospheric pollutants in the Mediterranean region, an experimental study was performed in an open-top chamber (OTC) facility. A mixture of six species representative of annual pastures was grown under field conditions inside the OTC. Plants were exposed for 39 days to four O3 treatments and three doses of N. The species responded heterogeneously to both factors. Legumes did not react to N but were very sensitive to O3: Trifolium species responded negatively, while Ornithopus responded positively, taking advantage of the greater sensitivity of clovers to O3. The grasses and the herb were more tolerant of O3 and grasses were the most responsive to N. Significant interactions between factors indicated a loss of effectiveness of N in O3-polluted atmospheres and an ability of O3 to counterbalance the damage induced by N input, but both effects were dependent on O3 and N levels. The inclusion of plant competition in the experimental design was necessary to reveal results that would otherwise be missed, such as the positive growth responses under elevated O3 levels. Surprisingly, competition within the legume family played the most important role in the overall response of the annual community to O3. Both tropospheric O3 and N deposition should be considered important drivers of the structure and biodiversity of Mediterranean annual pastures.

Lens density measurement with Scheimpflug camera in vitrectomised eyes. / Densidad critaliniana medida con cámara de Scheimpfug en ojos vitrectomizados.

OBJETIVE: To determine whether vitrectomised eyes have a higher lens optical density, when measured with a Scheimpflug camera, compared to non-vitrectomised eyes. METHOD: The peak and linear Scheimpflug optical density (DOS), and area of both eyes were measured in a sample size of 81 vitrectomised phakic patients. A comparison was made between the DOS of the vitrectomised eye lens and the contralateral non-vitrectomised eye using the Student-t test. RESULTS: A significantly higher linear DOS and area was obtained in the 81 vitrectomised phakic eyes when compared to the non-vitrectomised eyes (P<.001). The peak DOS is not significantly increased in respect to non-vitrectomised eyes (P=.59). CONCLUSIONS: The lens DOS in vitrectomised eyes is higher than in non-vitrectomised eyes. The importance of the vitreous in the maintenance of lens transparency is emphasised.

Identification of a non-haem catalase in Salmonella and its regulation by RpoS (sigmaS).

We report the identification and functional analysis of katN, a gene encoding a non-haem catalase of Salmonella enterica serotype Typhimurium. katN, which is not present in Escherichia coli, is located between the yciGFE and yciD E. coli homologues in the Salmonella genome. Its predicted protein product has a molecular weight of 31 826 Da and is similar to the Mn-catalases of Lactobacillus plantarum and Thermus spp. Its product, KatN, was visualized as a 37 kDa protein in E. coli maxicells. A KatN recombinant protein, containing six histidine residues at its C-terminus, was purified, and its catalase activity was observed on a non-denaturing polyacrylamide gel. KatN was also visualized by catalase activity gel staining of bacterial cell extracts. Its expression was shown to be regulated by growth phase and rpoS. Northern blotting indicated that kat forms an operon with the upstream yciGFE genes. A putative rpoS-regulated promoter was identified upstream of yciG. Southern blotting revealed that katN is conserved within Salmonella serovars. katN homologues were found in Pseudomonas aeruginosa, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae and Serratia marcescens. A katN mutation did not appear to affect the hydrogen peroxide (H2O2) response of Salmonella. However, the expression of katN increased the H2O2 resistance of unadapted cells in the exponential phase and of rpoS mutants in stationary phase. Thus, KatN may contribute to hydrogen peroxide resistance in Salmonella in certain environmental conditions.

Identification of RpoS (sigma(S))-regulated genes in Salmonella enterica serovar typhimurium.

The rpoS gene encodes the alternative sigma factor sigma(S) (RpoS) and is required for survival of bacteria under starvation and stress conditions. It is also essential for Salmonella virulence in mice. Most work on the RpoS regulon has been in the closely related enterobacterial species Escherichia coli. To characterize the RpoS regulon in Salmonella, we isolated 38 unique RpoS-activated lacZ gene fusions from a bank of Salmonella enterica serovar Typhimurium mutants harboring random Tn5B21 mutations. Dependence on RpoS varied from 3-fold to over 95-fold, and all gene fusions isolated were regulated by growth phase. The identities of 21 RpoS-dependent fusions were determined by DNA sequence analysis. Seven of the fusions mapped to DNA regions in Salmonella serovar Typhimurium that do not match any known E. coli sequence, suggesting that the composition of the RpoS regulon differs markedly in the two species. The other 14 fusions mapped to 13 DNA regions very similar to E. coli sequences. None of the insertion mutations in DNA regions common to both species appeared to affect Salmonella virulence in BALB/c mice. Of these, only three (otsA, katE, and poxB) are located in known members of the RpoS regulon. Ten insertions mapped in nine open reading frames of unknown function (yciF, yehY, yhjY, yncC, yjgB, yahO, ygaU, ycgB, and yeaG) appear to be novel members of the RpoS regulon. One insertion, that in mutant C52::H87, was in the noncoding region upstream from ogt, encoding a O(6)-methylguanine DNA methyltransferase involved in repairing alkylation damage in DNA. The ogt coding sequence is very similar to the E. coli homolog, but the ogt 5' flanking regions were found to be markedly different in the two species, suggesting genetic rearrangements. Using primer extension assays, a specific ogt mRNA start site was detected in RNAs of the Salmonella serovar Typhimurium wild-type strains C52 and SL1344 but not in RNAs of the mutant strains C52K (rpoS), SL1344K (rpoS), and C52::H87. In mutant C52::H87, Tn5B21 is inserted at the ogt mRNA start site, with lacZ presumably transcribed from the identified RpoS-regulated promoter. These results indicate that ogt gene expression in Salmonella is regulated by RpoS in stationary phase of growth in rich medium, a finding that suggests a novel role for RpoS in DNA repair functions.