Oxygen metabolism,oxidative stress and acid-base physiology of dental plaque biofilms

Dental plaque is a natural biofilm which has been a focus of attention for many years because of its known roles in caries and periodontal diseases. Acid production by plaque bacteria leads to the erosion of tooth mineral in caries, and the cariogenicity of plaque is related to population levels of acid-tolerant organisms such as mutants streptococci. However, the biofilm character of plaque allows for survival of a diverse flora, including less acid-tolerant organisms, some of which can produce ammonia from arginine or urea to counter acidification. Plaque is often considered to be relatively anaerobic. However, evidence is presented here that both supragingival and subgingival plaque have active oxygen metabolism and that plaque bacteria, including anaerobes, have developed defenses against oxidative stress. Even in subgingival plaque associated with periodontitis, measured residual oxygen levels are sufficient to allow for oxygen metabolism by organisms considered to be extremely anaerobic such asTreponema denticola, which metabolizes oxygen by means of NADH oxidases and produces the protective enzymes superoxide dismutase and NADH peroxidase. The finding that plaque bacteria produce a variety of protective enzymes is a good indicator that oxidative stress is a part of their everyday life. The biofilm character of plaque allows for population diversity and coexistence of aerobes, anaerobes and microaerophiles. Overall, agents that affect oxidative metabolism offer possibilities for reducing the pathogenic activities of plaque.     

Site selection by swans wintering in Britain and Ireland; the importance of habitat and geographic location

Monthly surveys of Bewick's Swans Cygnus columbianus bewickii , Whooper Swans Cygnus cygnus and Mute Swans Cygnus olor in Britain and Ireland were made during the 1990–1991 winter to determine factors affecting the swans' selection of feeding sites. Geographic location and habitat both influenced site selection. Whooper Swans occurred in greatest numbers at sites in Scotland, northeastern England and Northern Ireland, whereas Bewick's Swans had a more southerly distribution, reflecting differences in the migratory routes used by these two species. The resident Mute Swans were more widespread, with large flocks occurring in southeastern England and in parts of Scotland. Whooper and Mute Swans were found mainly on permanent inland waters (68% and 61%, respectively), but the majority of Bewick's Swans (60%) were on arable land. The percentage of Bewick's Swan flocks found on permanent inland waters (42%) was higher than that found on arable fields (23%), indicating that the large number recorded on arable land was a result of the birds congregating at a comparatively small number of sites. Overall, less than 15% of Whooper Swans and 3% of Mute Swans were on arable crops during the winter, but the largest flocks were associated with arable land for all three species. Thus, although the occurrence of large flocks at particular arable sites may give an impression that swans feed mainly on farmland, the swans are in fact more widely dispersed. Regional variation in the percentage of juveniles present was recorded for all three species. Changes during the winter in the distribution of juveniles, and of the swans as a whole, are considered in relation to food supply and to migratory routes for the Bewick's and Whooper Swans.     

Herpes simplex virus 2 causes apoptotic infection in monocytoid cells

Increasing evidence indicates that apoptosis can be associated with several viral infections. Here we demonstrate, that infection of monocytoid cells by Herpes simplex virus 2 (HSV-2) resulted, in time- and dose-dependent induction of apoptosis as an exclusive cytopathic effect. The phenomenon was confirmed using four different techniques. Conversely, apoptosis was not observed in the Vero cell line. Virus yield in monocytoid cells was delayed and reduced, although well detectable, in comparison with that observed in Vero cells. Nevertheless, released virions exhibited full infecting capability. Apoptosis induced by HSV-2 was not inhibited by cycloheximide and only partially by an UV-treatment which completely abrogated infectivity. Virus-induced apoptosis was partly inhibited by indomethacin and was associated with a down-regulation of Bcl-2. A similar, but less pronounced, apoptosis-inducing effect in monocytoid cells was also observed with HSV-1 infection. Depending on the target cells, therefore, HSV could complete a cycle of infection which is characterized by apoptosis of infected cells.     

Chromosomal localization of a tandemly repeated DNA sequence in Trifolium repens L

INTRoDUCTIoNlYho1iumrePensL,whiteclover,isaneconomicallyimportantplantspeciesintemperatepastures.Asbrieflyreportedby[1],ithas16pairsofchromosomes(2n=32).Asyet,nodetailedcytologicalexaminationofthisspecies,suchasC-banding,hasbeenrep0rted.Inthelastdecade,thetechnique0fC-bandinghasbeenusedt0examinehighlyrepeatedsequencesinplantchrom0s0mesandhasprovidedausefultoolf0rtheanalysis0fcyt0geneticstructureincr0pplants[2-71.Inplants,thechr0m0s0mall0calizationofhighlyrepeatedDNAsequencesbyinsituhybr…