Unambiguous detection and improved quantification of phagotrophy in apochlorotic nanoflagellates using fluorescent microspheres and concomitant phase contrast and epifluorescence microscopy

Recent procedures for quanhfying the ingestion of non-nutritive bacterial sized particles by bacterivores lack the necessary resolution for the accurate determination of ingestion rates. Here, we descnbe how the filter-transfer-freeze procedure of Hewes & Holm-Hansen (1983) permits concomitant epifluorescence and phase contrast microscopy which lets us unambiguously discriminate between lngested and non-ingested fluorescent microspheres (FM) in 4 specles of apochlorotic nanoflagellates. This rapid procedure reduces the subjectivity of grazing rate determlnations while improving precision. We have used this procedure to observe non-continuous feeding, egestion processes and the effect of growth inhibition on phagotrophy.