ABSTRACT
In a study of bacterioplankton in an oligotrophic lake in northern Wisconsin, a community fingerprinting technique, automated ribosomal intergenic spacer analysis (ARISA), was used to determine the effect of resources and trophic interactions on bacterioplankton diversity. Inorganic nitrogen and phosphorus (NP), carbon in the form of glucose (G) or dissolved organic matter extracted from peat (DOM), and carbon and NP in combination were added to two types of experimental systems. Ten-liter mesocosms contained all components of the original aquatic community except for large zooplankton. One-liter dilution cultures were prepared so that the effects of grazers and phytoplankton were removed. During a 3-day incubation, bacterial production showed the greatest response to the carbon plus NP treatment in both experimental systems, but bacterial diversity was strikingly different between them. In the mesocosms, the number of ARISA-PCR fragments averaged 41 per profile, whereas the dilution culture communities were highly reduced in complexity, dominated in most cases by a single PCR fragment. Further analysis of the mesocosm data suggested that whereas the NPDOM addition caused the greatest aggregate bacterial growth response, the addition of NP alone caused the largest shifts in community composition. These results suggest that the measurement of aggregate responses, such as bacterial production, alone in studies of freshwater bacterial communities may mask the effects of resources on bacterioplankton.
ABSTRACT
BACKGROUND: For logistical reasons sedation studies are often carried out in elective surgical patients and the results extrapolated to the general intensive care unit (ICU) population. We question the validity of this approach. We compared the two sedation regimens used in our general ICU in a trial structured to mimic clinical practice as closely as possible. RESULTS: Forty patients were randomised to intermittent diazepam or continuous midazolam and sedation monitored with hourly sedation scores; 31 patients completed the study. Scores indicating undersedation were more common with diazepam (P <0.01); overall adequate sedation midazolam 64.7%, diazepam 35.7% (P =0.21). No patient exhibited inappropriately prolonged sedation. Cost was: midazolam AUS$1.98/h; diazepam AUS$0.06/h. CONCLUSION: Both regimens produced rapid onset of acceptable sedation but undersedation appeared more common with the cheaper diazepam regimen. At least 140 patients should be studied to provide evidence applicable to the general ICU population. Used alone, a sedation score may be an inappropriate outcome measure for a sedation trial.
ABSTRACT
Abstract Bacterial abundance, temperature, pH, and dissolved organic carbon (DOC) concentration were compared across surface sites within and between two northern Wisconsin Sphagnum peatlands over the summer seasons in 1995 and 1996. Sites of interest were the Sphagnum mat surface, the water-filled moat (lagg) at the bog margin, and the bog lake littoral zone. Significant differences in both bacterial populations and water chemistry were observed between sites. pH was highest in the lake and lowest in the mat at both bogs; the opposite was true for DOC. Large populations of bacteria were present in surface interstitial water from the mat; abundance in this site was consistently higher than in the moat or lake. Bacterial abundance also increased across sites of increasing DOC concentration and declining pH. Bacterial activities (rates of [3H]leucine incorporation) and growth in dilution cultures (with grazers removed) were also assessed in lake, moat, and mat sites. Results using these measures generally supported the trends observed in abundance, although high rates of [3H]leucine incorporation were recorded in the moat at one of the bogs. Our results indicate that bacterial populations in Sphagnum peatlands are not adversely affected by acidity, and that DOC may be more important than pH in determining bacterial abundance in these environments.
ABSTRACT
Epiphytic bacterial communities within the sheath material of three filamentous green algae, Desmidium grevillii, Hyalotheca dissiliens, and Spondylosium pulchrum (class Charophyceae, order Zygnematales), collected from a Sphagnum bog were characterized by PCR amplification, cloning, and sequencing of 16S ribosomal DNA. A total of 20 partial sequences and nine different sequence types were obtained, and one sequence type was recovered from the bacterial communities on all three algae. By phylogenetic analysis, the cloned sequences were placed into several major lineages of the Bacteria domain: the Flexibacter/Cytophaga/Bacteroides phylum and the alpha, beta, and gamma subdivisions of the phylum Proteobacteria. Analysis at the subphylum level revealed that the majority of our sequences were not closely affiliated with those of known, cultured taxa, although the estimated evolutionary distances between our sequences and their nearest neighbors were always less than 0.1 (i.e., greater than 90% similar). This result suggests that the majority of sequences obtained in this study represent as yet phenotypically undescribed bacterial species and that the range of bacterial-algal interactions that occur in nature has not yet been fully described.
