Acetate utilization (¹⁴C tracer) experiments

This procedure was carried out on the sample vials that had previously been processed for acetate methanogenesis (see relevant section).

These vials were butyl-rubber stoppered glass vials (30 ml) containing the slurried sample (approx 6 cm3 of sediment in 7 ml of 1 M NaOH). Any acetate that had been utilized by bacteria will have been converted to CO2 and would be trapped in the NaOH.

The contents of the glass vial are emptied into a 100 ml flat-bottomed, long-neck (Quickfit) flask and the vial rinsed with 2 x 10 ml of Milli-Q water to ensure complete sample transfer. A magnetic follower (12 mm) is added.

20 ml of 1 M HCl is introduced to the flask by injection through the septum to acidify the sample and release CO2. The slurry is stirred rapidly for 20 minutes and the flushed headspace passed through to the scintillation vials. The scintillation vials are then counted on a scintillation counter.

The results are processed through the relevant spreadsheet to obtain potential rate measurements. An isotope discrimination factor of 1.06 was used. Additionally, the obtained dpm (disintegrations per minute) from the scintillation counter were doubled to account for the fact that the isotope was a 50:50 mixture of 1-C and 2-C labeled acetate.

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