A fluorochrome‐staining technique for counting bacteria in saline, organically enriched, alkaline lakes

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Abstract
A procedure is described for epifluorescence direct‐counting of planktonic bacteria in an alkaline, hypersaline, organically enriched lake. To preclude precipitation and staining of dissolved organic material (DOM), the procedure involved isotonic dilution of unfixed samples at in situ pH and filtration before fluorochrome staining. Fluorochrome‐DOM complexes remaining on the filter were removed by sequential rinses with isotonic 0.1 M citrate (pH 6.6). With the modified procedure, the dye acridine orange (AO) yielded better specimen‐background contrast and higher overall cell counts than did ethidium bromide, Hoechst dye No. 33258, or 4,6‐diamidino‐2‐phenylindole (DAPI).