Measurement of the effects of cadmium stress on protozoan grazing of bacteria (bacterivory) in activated sludge by fluorescence microscopy.
AUTOR(ES)
Hoffman, R L
RESUMO
The effect of cadmium stress on protozoan bacterivory in sewage sludge was measured by experimentally exposing sludge communities to 0 to 150 mg of Cd per liter for up to 6 h and then determining the rates of protozoan grazing on bacteria, using a double-staining technique and epifluorescence microscopy. Bacterivory was measured by incubating the sludge with fluorescently labeled bacterium-sized latex beads and directly observing ingestion of the beads and bacterial cells in the sludge by epifluorescence microscopy of preserved samples. Staining with 4',6-diamidino-2-phenylindole and acridine orange permitted the simultaneous determination of protozoan numbers and bacterivory activity as estimated by the number of bacterial cells and bacterium-sized latex beads ingested by the representative ciliate Aspidisca costata. Enumeration with latex beads proved to be an effective way of estimating bacterivory in sludges subjected to heavy-metal stress. This technique should prove useful for determining the effects of other chemical stresses on protozoan numbers and bacterivory in organic-rich environments. Although the number of protozoa declined significantly only after exposure to 100 mg of Cd per liter for 4 h, grazing, as indicated by bead ingestion, was significantly inhibited by Cd concentrations of greater than 25 mg/liter in less than 1 h, and exposure to 100 mg of Cd per liter effectively stopped protozoan grazing within 1 h of exposure. Protozoan ingestion of latex beads and bacteria was inversely correlated to Cd concentration and exposure time. The reduction of protozoan bacterivory by Cd provides a possible explanation for the increase in suspended bacteria in the effluents of metal-stressed treatment facilities.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=204126Documentos Relacionados
- Improved identification of methanogenic bacteria by fluorescence microscopy.
- Use of nuclepore filters for counting bacteria by fluorescence microscopy.
- Observation of single influenza virus-cell fusion and measurement by fluorescence video microscopy.
- Fluorescence lifetime imaging by asynchronous pump-probe microscopy.
- Effect of growth rate and hydrophobicity on bacteria surviving protozoan grazing.