Regulation of the penicillinase genes of Bacillus licheniformis: interaction of the pen repressor with its operators.

The synthesis of the inducible enzyme penicillinase of Bacillus licheniformis is negatively controlled by a repressor (D.A. Dubnau and M.R. Pollock, J. Gen. Microbiol. 41:7-21, 1965; D. J. Sherratt and J. F. Collins, J. Gen. Microbiol. 76:217-230,1973). The molecular organization of the genes coding for penicillinase (penP) and its repressor (penI) has recently been determined (T. Himeno, T. Imanaka, and S. Aiba, J. Bacteriol. 168:1128-1132, 1986). These two genes are transcribed divergently from within a 364-nucleotide region separating the coding sequences. We cloned and sequenced the repressor gene (penIc) from strain 749/C that constitutively produces penicillinase. The penIc and penI+ (wild-type) genes were expressed in Escherichia coli. Complementation analysis indicated that the repressor is the only trans-acting protein required to regulate the expression of the penI and penP genes. We purified the wild-type repressor protein, used it in gel retardation and DNase I protection experiments, and identified three operators positioned in the region between the penP and penI coding sequences. The spatial arrangement of the operators and the hierarchy in repressor binding seen in the protection experiments indicate that (i) the penI gene product represses the expression of the penP gene by physically blocking the RNA polymerase-binding site and (ii) the penI gene is autoregulated.     

The effect of propargylic substitution on the activation and aromatization of enediynes

The thiol activation and aromatization of bicyclo[7.1.0]enediynes was found to be dependent of the nature of the propargyl substituent. These effects are correlated to antitumor activity.     

Herbivory and drought interact to enhance spatial patterning and diversity in a savanna understory

The combination of abiotic stress and consumer stress can have complex impacts on plant community structure. Effective conservation and management of semi-arid ecosystems requires an understanding of how different stresses interact to structure plant communities. We explored the separate and combined impacts of episodic drought, livestock grazing, and wild ungulate herbivory on species co-occurrence and diversity patterns in a relatively productive, semi-arid Acacia savanna. Specifically, we analyzed 9 years of biannual plant community data from the Kenya long-term exclosure experiment, a broad-scale manipulative experiment that has excluded different combinations of large mammalian herbivores from 18 4-ha plots since 1995. During droughts, we observed low species diversity and random species co-occurrence patterns. However, when rain followed a major drought, areas exposed to moderate cattle grazing displayed high species diversity and evidence of significant species aggregation. These patterns were not apparent in the absence of cattle, even if other large herbivores were present. To explore possible mechanisms, we examined patterns separately for common and rare species. We found that aggregation patterns were likely driven by rare species responding similarly to the availability of open micro-sites. Our results indicate that in a productive, fire-suppressed savanna, the combination of periodic drought and moderate cattle grazing can enhance plant biodiversity and fine-scale spatial heterogeneity by opening up space for species that are otherwise rare or cryptic. Our findings also emphasize that domestic herbivores can have significantly stronger impacts on plant community dynamics than wild herbivores, even in an ecosystem with a long history of grazing.     

Spatial distribution of Culicoides species in Portugal in relation to the transmission of African horse sickness and bluetongue viruses

Surveillance of Culicoides (Diptera: Ceratopogonidae) biting midge vectors was carried out at 87 sites within a 50 x 50 km grid distributed across Portugal, using light trap collections at the time of peak midge abundance. Culicoides imicola (Kieffer) made up 66% of the 55 937 Culicoides in these summer collections. It was highly abundant in the central eastern portion of Portugal, between 37 degrees 5' N and 41 degrees 5' N, and in a band across to the Lisbon peninsula (at around 38 degrees 5' N). Of all the complexes, its distribution was most consistent with that of previous outbreaks of Culicoides-borne disease, suggesting that it may remain the major vector in Portugal. Its distribution was also broadly consistent with that predicted by a recent climate-driven model validating the use of remote sensing datasets for modelling of Culicoides distribution. Adult C. imicola were found to have overwintered at 12 of 20 sites re-surveyed in winter but it did so in very low numbers. Culicoides obsoletus (Meigen) and Culicoides pulicaris (Linnaeus) complex midges were widespread despite their low summer abundance. The observed coincidence of high abundances of C. imicola and high abundances of C. pulicaris in summer lead us to suggest that C. imicola could bring African horse sickness virus or bluetongue virus into contact with C. pulicaris and the latter complex, together with C. obsoletus, could then transmit these viruses across much wider areas of Europe. The fact that adult C. pulicaris are present in high abundances in winter may provide a mechanism by which these viruses can overwinter in these areas.     

Protocol of a prospective study on the diagnostic value of transcranial duplex scanning of the substantia nigra in patients with parkinsonian symptoms

Background  

Parkinson's disease (PD) is the second most common neurodegenerative disorder. As there is no definitive diagnostic test, its diagnosis is based on clinical criteria. Recently transcranial duplex scanning (TCD) of the substantia nigra in the brainstem has been proposed as an instrument to diagnose PD. We and others have found that TCD scanning of substantia nigra duplex is a relatively accurate diagnostic instrument in patients with parkinsonian symptoms. However, all studies on TCD so far have involved well-defined, later-stage PD patients, which will obviously lead to an overestimate of the diagnostic accuracy of TCD.     

The effects of fire, local environment and time on ant assemblages in fens and forests

We investigated the effects of the abiotic environment, plant community composition and disturbance by fire on ant assemblages in two distinct habitat types in the Siskiyou Mountains in northern California and southern Oregon, USA. Sampling over 2 years in burned and unburned Darlingtonia fens and their adjacent upland forests, we found that the effects of disturbance by fire depended on habitat type. In forests, fire intensity predicted richness in ant assemblages in both years after the fire, and plant community composition predicted richness 2 years after the fire. No factors were associated with richness in the species‐poor fen ant assemblages. Species‐specific responses to both habitat type and disturbance by fire were idiosyncratic. Assemblage composition depended on habitat type, but not disturbance by fire, and the composition of each assemblage between years was more dissimilar in burned than unburned sites.