Methods of estimating bacterivory by protozoa

摘要

Bacterivory by protozoa has been measured by several techniques in laboratory cultures and in natural marine samples from eutrophic, mesotrophic and oligotrophic waters. Different techniques are recommended for use in different situations. Direct counting and biomass (protein) measurement techniques work well on laboratory cultures; thus 120 Vibrio bacteria were consumed for each new flagellate (Pteridomonas danica) produced, with a gross growth efficiency (GGE) of 43 %. Methods using dual radioactive labelled bacterial prey have been used to measure both grazing and assimilation rates in laboratory and marine samples. At high bacterial concentrations cultured P. danica ingested on average 4-5 Vibrio h(-1), while the smaller Paraphysomonas imperforata ingested 10 Vibrio h(-1); under these conditions flagellates accumulated only 20% of bacterial biomass. In an open sea sample 18% of the bacterial standing stock were consumed in 13 hours, with a GGE of about 50%. Fluorescently-labelled bacteria techniques uniquely provide information about the diet of predators, but have strict limitations; these revealed that only half of a population of P. danica consumed any Vibrio from a concentration of 2.2 x 10(6) bacteria ml(-1) in the first hour, and those which did feed ingested 6-7 bacteria each. Glucosaminidase enzyme concentrations in particulate fractions of natural samples correlate strongly with heterotrophic eukaryote biomass, and provide the basis of a biomass assay. [References: 15]