Qualitative importance of the microbial loop and plankton community structure in a eutrophic lake during a bloom of cyanobacteria

Plankton community structure and major pools and fluxes of carbon were observed before and after culmination of a bloom of cyanobacteria in eutrophic Frederiksborg Slotssø, Denmark. Biomass changes of heterotrophic nanoflagellates, ciliates, microzooplankton (50 to 140 μm), and macrozooplankton (larger than 140 μm) were compared to phytoplankton and bacterial production as well as micro- and macrozooplankton ingestion rates of phytoplankton and bacteria. The carbon budget was used as a means to examine causal relationships in the plankton community. Phytoplankton biomass decreased and algae smaller than 20 μm replacedAphanizomenon after the culmination of cyanobacteria. Bacterial net production peaked shortly after the culmination of the bloom (510 μg C liter^?1 d^?1 and decreased thereafter to a level of approximately 124 μg C liter^?1 d^?1. Phytoplankton extracellular release of organic carbon accounted for only 4–9% of bacterial carbon demand. Cyclopoid copepods and small-sized cladocerans started to grow after the culmination, but food limitation probably controlled the biomass after the collapse of the bloom. Grazing of micro- and macrozooplankton were estimated from in situ experiments using labeled bacteria and algae. Macrozooplankton grazed 22% of bacterial net production during the bloom and 86% after the bloom, while microzooplankton (nauplii, rotifers and ciliates larger than 50 μm) ingested low amounts of bacteria and removed 10–16% of bacterial carbon. Both macro-and microzooplankton grazed algae smaller than 20 μm, although they did not control algal biomass. From calculated clearance rates it was found that heterotrophic nanoflagellates (40–440 ml^?1) grazed 3–4% of the bacterial production, while ciliates smaller than 50 μm removed 19–39% of bacterial production, supporting the idea that ciliates are an important link between bacteria and higher trophic levels. During and after the bloom ofAphanizomenon, major fluxes of carbon between bacteria, ciliates and crustaceans were observed, and heterotrophic nanoflagellates played a minor role in the pelagic food web.     

Structural analysis of the operator binding domain of Tn10-encoded Tet repressor: a time-resolved fluorescence and anisotropy study.

An engineered Tn10-encoded Tet repressor, bearing a single Trp residue at position 43, in the putative alpha-helix-turn-alpha-helix motif of the operator binding domain, was studied by time-resolved fluorescence and anisotropy. Fluorescence intensity decay data suggested the existence of two classes of Trp-43, defined by different lifetimes. Analysis of anisotropy data were consistent with a model in which each class was defined by a different lifetime, rotational correlation time, and fluorescence emission maximum. The long-lifetime class had a red-shifted spectrum, similar to that of tryptophan zwitterion in water, and a short rotational correlation time. In contrast, the spectrum of the short-lifetime class was blue-shifted 10 nm compared to that of the long-lifetime class. Its correlation time was similar to that of the protein, which showed that Trp in this class was entirely constrained. Trp in this latter class could not be quenched by iodide, whereas most of the long-lifetime class was easily accessible. Presence of disruptive agents, such as 1 M GuCl or 3 M KCl, did not alter markedly the lifetimes but increased the weight of the short-lifetime component. In the same time, the rotational correlation time of this component was dramatically reduced. Taken together, our data suggest that the long-lifetime class could correspond to the tryptophan residues exposed to solvent whereas the short-lifetime class would correspond to the tryptophan residues embedded inside the hydrophobic core holding the helix-turn-helix motif. Destabilization of hydrophobic interactions would lead to an increase in the weight of the latter class for entropic reasons. Analysis of the fluorescence parameters of Trp-43 could provide structural information on the operator binding domain of Tet repressor.     

High dose antioxidant supplementation to MS patients. Effects on glutathione peroxidase, clinical safety, and absorption of selenium.

High-dose antioxidant supplementation has recently been recommended for multiple sclerosis (MS) patients. This study tests the clinical safety, the glutathione peroxidase (GSH-px) activity, and the absorption of selenium during such supplementation. Eighteen MS patients were given 6 tablets especially made for this study, equivalent to 6 mg sodium selenite, 2 g vitamin C, and 480 mg vitamin E a day for five wk. GSH-px, which was lower than in non-MS controls before the start of treatment, increased fivefold during 5 wk of treatment. Side effects were scarce. Ten MS patients were subjected to a 24-h selenium absorption study after ingestion of 2 active tablets, equivalent to 2 mg sodium selenite. Selenium, which was low initially, increased 24% during the first 3 h and then stabilized. It is concluded that the tested antioxidant treatment seems to be safe and that MS patients have low GSH-px, which may be increased by the tested antioxidant treatment.     

Bacteria associated with a marine planktonic copepod in culture. I. Bacterial genera in seawater, body surface, intestines and fecal pellets and succession during fecal pellet degradation

In laboratory experiments, the bacterial flora of the zooplanktonmicrobial environments seawater, fecal pellets and associatedwith the external and internal surfaces of the copepod Acartiatonsa(Dana) were examined. The bacteria associated with fecal pelletswere dominated by Bacillus spp., Cytophaga/Flavobacterium spp.,Vibrio spp. and Pseudomonas spp. The same genera were foundin the seawater (0.22 7mu;m filtered) in which the pellets wereincubated. The bacteria showed a characteristic growth succession,and the abundance increased several orders of magnitude in theseawater during incubation of the pellets, indicating growthand proliferation based on the disintegrating/degrading fecalpellets. A carbon budget calculation revealed that organic matterfrom degrading fecal pellets could cover the carbon demand forthe growing bacterioplankton. The composition of the bacterialcommunity in the seawater and the fecal pellets also indicateda colonization of the pellets from bacterioplankton. The compositionof the bacteria associated with the copepods showed that bacterialgenera characterized as surface associated were preferentiallyassociated with fecal pellets, animal surfaces and intestines.This suggests a specific intestinal flora in the cultivatedcopepods composed of 10³ culturable bacteria per intestine (colony-formingunits, c.f.u.) or 10⁵ bacteria per intestine (acridine orangedirect counts, AODC), possibly colonizing the intestine passivelyduring filtration of algae. The activity of the bacterial communitieswas examined by the numencal ratio c.f.u.:AODC, where 1–19%of the bacteria were found active, with no significant differencebetween microbial environments.     

Inhibitory Effects of Secondary Metabolites from the Red Alga Delisea pulchra on Swarming Motility of Proteus mirabilis

Abnormal, uncoordinated swarming motility of the opportunistic human pathogen Proteus mirabilis was seen when a crude extract of the Australian red alga Delisea pulchra was added to the medium. This occurred at concentrations at which growth rate, swimming motility, cell elongation, polynucleation, and hyperflagellation were not affected. One halogenated furanone from D. pulchra inhibited swarming motility at concentrations that did not affect growth rate and swimming motility. Other structurally similar D. pulchra furanones had no effect on swarming, suggesting considerable specificity in the effects of furanones on swarming motility by P. mirabilis.     

MORBILLIVIRUS INFECTION IN BOTTLENOSE DOLPHINS: EVIDENCE FOR RECURRENT EPIZOOTICS IN THE WESTERN ATLANTIC AND GULF OF MEXICO

Morbillivirus infection is widespread among odontocetes of the western Atlantic and Gulf of Mexico. Serologic evidence of infection in bottlenose dolphins, Tursiops truncatus , was first detected during an epizootic along the mid-Atlantic coast in 1987. Here, we report recurrent epizootics in the coastal dolphin population since at least the early 1980s based on serological surveys and regional stranding frequencies. The first observed epizootic of this series occurred in the Indian and Banana Rivers in 1982 and was followed by others on the mid-Atlantic coast in 1987–1988 and in the Gulf of Mexico between 1992 and 1994. This temporal pattern of infection is likely facilitated by the population size and its fragmentation into relatively discrete coastal communities. Introduction of morbillivirus into a community with a sufficient number of naive hosts may precipitate an epizootic, depending on the potential for transmission within the group. Propagation of an epizootic along the coast is probably determined by frequency of contact between adjacent communities and seasonal migrations.
Morbillivirus antibodies were also detected in serum from offshore bottlenose dolphins. The sero-prevalence in the latter may be higher than in coastal dolphins because of their close association with enzootically infected pilot whales ( Globicephala spp.). Occasional contact between offshore and coastal dolphins may provide an epizootiologic link between pilot whales and coastal dolphin communities.