Measuring Epilithic Bacterial Production In Streams

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Abstract
Techniques are presented for the measurement of bacterial production (by the rate of 3H-TdR incorporation into DNA), isotope dilution, time course of incorporation of nucleoside, and disturbance artifacts in natural epilithic (on rock) communities of headwater streams. The epilithon in riffles was subsampled by carefully chipping upper rock surfaces. Chips were placed in test tubes and incubated in situ. Test tubes were rotated to reduce the formation of artificial diffusion barriers to TdR transport. DNA was isolated using a double filtration technique. Summertime production had a range of 1.3–51 mg C∙m−2∙h−1 in five southern Ontario streams. Precursors to DNA synthesis, which diluted 3H-TdR, had a range of 63–440 nM. Incorporation of 3H-TdR was linear for at least 1 h. Disturbance artifacts did not appear from rock chipping or from extended sample rotation. The techniques can be applied to other microbial groups from various aquatic hard substrata.