University of Bergen

About: University of Bergen is a education organization based out in Bergen, Hordaland, Norway. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 17106 authors who have published 52492 publications receiving 2009844 citations. The organization is also known as: Universitetet i Bergen & Universitas Bergensis.

P limitation of heterotrophic bacteria and phytoplankton in the northwest Mediterranean

Abstract: Surface-water microbial populations were investigated in the northwest Mediterranean for possible indicators of phosphate deficiency and limitation. Low phosphorus availability was suggested by short turnover time (min. observed 0.68 h), high-alkaline phosphatase activity (V,,,,, = 28 nM hydrolyzed h-l), subsaturation of phosphate uptake (2.6-9% of V,,,), and high-pulse uptake capacity of added orthophosphate. Based on high pulse uptake capacity and subsaturated uptake in both the >l-pm and in the 0.2-l-pm size fractions, P deficiency is suggested for both phytoplankton and heterotrophic bacteria. P limitation of heterotrophic bacteria was also supported by fast positive responses after phosphate addition in both thymidine incorporation in whole-water samples and increased bacterial cell numbers in predator-free water. No effects were found after addition of carbon or nitrogen sources alone. Combined with other published evidence, we suggest that the growth rates of not only phytoplankton, but also of heterotrophic bacteria, are P limited in this environment in summer. The finding has important implications for the dynamics of accumulation of dissolved organic carbon in the photic zone and thus for the carbon cycle of oceans. The generally oligotrophic state of the Mediterranean Sea has traditionally been explained as a consequence of its antiestuarine circulation; the net evaporation from the Mediterranean produces an inflow of low-nutrient surface water through the Gibraltar and an eastward surface current in the Mediterranean (Redfield et al. 1963). If one combines an assumption of nitrogen-limited growth in the inflowing Atlantic water with the usual assumption of a faster recycling of phosphorus than of nitrogen, one might expect a strong nitrogen limitation in the upper photic zone during Mediterranean summer stratification. Contrary to such an expectation, accumulated experimental data seem to indicate that parts of the Mediterranean are characterized by a nitrate : phosphate ratio below Redfield (Krom et al. 1991). This seems to be particularly prominent in the eastern parts of the Mediterranean (Krom et al. 1991) and in the Adriatic Sea (Vukadin and Stojanski 1976). In an investigation of orthophosphate uptake in surface water from Villefranche Bay on the French Mediterranean coast, Dolan et al. (1995) found relatively short turnover times (down to 1.6 h). Estimates of bioavailable orthophosphate concentrations in this area (Thingstad et al. 1995) are also very low (0.8 nM), indicating, but not proving, that P may be the limiting nutrient also in this part of the western Mediterranean. The underlying biogeochemical mechanisms behind such an apparent shift toward P deficiency seem still to be unknown,

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum.

Abstract: The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.