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P Casper

Publications and source records attributed to P Casper.

10 recordsLinked to original sources
PubMed2004

Methanogenic pathway and archaeal community structure in the sediment of eutrophic Lake Dagow: effect of temperature.

Methanogenic degradation of organic matter is an important microbial process in lake sediments. Temperature may affect not only the rate but also the pathway of CH4 production by changing the activity and the abundance of individual microorganisms. Therefore, we studied the function and structure of a methanogenic community in anoxic sediment of Lake Dagow, a eutrophic lake in north-eastern Germany. Incubation of sediment samples (in situ 7.5 degrees C) at increasing temperatures (4, 10, 15, 25, 30 degrees C) resulted in increasing production rates of CH4 and CO2 and in increasing steady-state concentrations of H2. Thermodynamic conditions for H2/CO2 -dependent methanogenesis were only exergonic at 25 and 30 degrees C. Inhibition of methanogenesis with chloroform resulted in the accumulation of methanogenic precursors, i.e., acetate, propionate, and isobutyrate. Mass balance calculations indicated that less CH4 was formed via H2 at 4 degrees C than at 30 degrees C. Conversion of 14CO2 to 14CH4 also showed that H2/CO2 -dependent methanogenesis contributed less to total CH4 production at 4 degrees C than at 30 degrees C. [2-14 C]Acetate turnover rates at 4 degrees C accounted for a higher percentage of total CH4 production than at 30 degrees C. Collectively, these results showed a higher contribution of H2-dependent methanogenesis and a lower contribution of acetate-dependent methanogenesis at high versus low temperature. The archaeal community was characterized by cloning, sequencing, and phylogenetic analysis of the 16S rRNA genes retrieved from the sediment. Sequences were affiliated with Methanosaetaceae, Methanomicrobiaceae, and three deeply branching euryarchaeotal clusters, i.e., group III, Rice cluster V, and a novel euryarchaeotal cluster, the LDS cluster. Terminal restriction fragment length polymorphism (T-RFLP) analysis showed that 16S rRNA genes affiliated to Methanosaetaceae (20-30%), Methanomicrobiaceae (35-55%), and group III (10-25%) contributed most to the archaeal community. Incubation of the sediment at different temperatures (4-30 degrees C) did not result in a systematic change of the archaeal community composition, indicating that change of temperature primarily affected the activity rather than the structure of the methanogenic community.

Archaea↗
PubMed2001

Bacterioplankton abundance, biomass and production in a Brazilian coastal lagoon and in two German lakes.

The bacterioplanktonic abundance, biomass, and production within a tropical lagoon (Cabiúnas, Brazil) and two temperate lakes (Stechlin and Dagow, Germany) were compared. Bacterial abundance and production were significantly different among the three water bodies. The lowest bacterial production (0.8 microg C l(-1) d(-1)) was observed in the tropical Cabiúnas Lagoon despite its higher mean temperature and dissolved organic carbon concentration. Highest bacterioplankton abundance (2.6 x 10(9) cells l(-1)) and production (68.5 microg C l(-1) d(-1)) were measured in eutrophic Lake Dagow. In oligotrophic Lake Stechlin, the lowest bacterial biomass (48.05 microg C l(-1)) was observed because of lower bacterial biovolume (0.248 microm(3)) and lower bacterial abundance. Bacterial populations in the temperate lakes show higher activity (production/biomass ratio) than in the tropical lagoon. The meaning of isotopic dilution and leucine incorporation by non-bacterial micro-organisms were evaluated in the oligotrophic temperate system. Leucine uptake by non-bacterial micro-organisms did not have significant influence on bacterial production.

Animals↗
PubMed2000

Different methods for extracting bacteria from freshwater sediment and a simple method to measure bacterial production in sediment samples.

The efficiency of different treatments was tested to extract bacterial cells from freshwater sediment samples. The influence of sonication, density gradient centrifugation, fixation by formalin and centrifugation speed on bacterial recovery was investigated. The method developed by Smith and Azam [Mar. Microb. Food Webs 6 (1992) 107] to measure microbial activity on bacterioplankton (3H-leucine incorporation), was also evaluated in sediment samples. After 1 min of sonication bacterial abundance was reduced by about 47% in diluted sediments with tetrasodium pyrophosphate. With the addition of Percoll after sonication, bacterial counts were not significantly different (P<0.05). Fixation by formalin increased bacterial counts using sonication. However, higher bacterial abundance was estimated in non-sonicated samples. Bacterial abundance in samples centrifuged at 7000xg with and without Percoll was not significantly different (P<0.05). Highest bacterial abundance was obtained after centrifugation at low speed (750xg). Bacterial abundance decreased with higher centrifugation speed (750, 1500 and 3000xg), the difference, however, was not significant. Bacterial production ranged from 0.10 microg C cm(-3) d(-1) in autoclaved sediment to 0. 27 microg C cm(-3) d(-1) in untreated sediment. The radioactivity measured in controls of both untreated and autoclaved sediment was high (70 and 91%, respectively), indicating a high level of leucine adsorption in sediment particles. In contrast, radioactivity in control samples previously centrifuged was markedly lower (6%). Despite the high values of radioactivity in the controls, bacterial production in untreated sediment was significantly higher than in centrifuged sediment (P<0.05).

Bacteria↗
PubMed1983

[General control of amino acid biosynthesis in mutants of Candida spec. EH 15/D].

The general control of amino acid biosynthesis was investigated in Candida spec. EH 15/D, using single and double mutant auxotrophic strains and prototrophic revertants starved for their required amino acids. These experiments show that starvation for lysine, histidine, arginine, leucine, threonine, proline, serine, methionine, homoserine, asparagine, glutamic acid or aspartic acid can result in derepression of enzymes. A correlation was found between the degree of derepression, growth of strains, and concentration of required amino acids. The amino acids pool pattern of mutants and revertants is different from that in the wild type strain.

Amino Acids↗
PubMedDate not supplied

[Bipolar disorder in children and adolescents].

Bipolar disorder affects all age categories, included children and adolescents (in this case, prepubertal and early adolescent or PEA-BP). Its diagnosis at this age is difficult for two reasons: first, clinical symptoms are different from these encountered by adults and second, an important psychiatric comorbidity is often observed (especially with attention-deficit/hyperactivity disorder or ADHD). This review presents the clinical presentation, the differential diagnosis, the familial antecedents, the comorbidity and the treatment of the PEA-BP.

Adolescent↗