Microaerophilic bacterial biomass measurements based on Adenosine Triphosphate and direct counting techniques in a semi-solid agar column

Abstract

Microaerophilic-diazotrophic bacterial biomass was measured by Adenosine Triphosphate (ATP) extraction and direct counting/biovolume techniques. Microaerophilic bacterial growth in a semi-solid agar column is visible in the form of sharp, well-defined growth rings at different depths within the column according to oxygen requirements. The microaerophilic zone is found between 3 and 15 mm below the agar surface, where the dissolved oxygen concentration varies from 4 to 172 µM. Biomass measurements calculated using a conventional conversion factor C/ATP of 250 were around ten times lower than those calculated according to the direct counting/biovolume technique. In the present study, we propose a conversion factor of 356 µg C/mL ATP that gives biomass measurements nearer to those obtained by direct counting. The highest bacterial metabolic activity was found between 5 and 10 mm depth (0.15 ± 0.029 µg ATP mL^–1), coinciding with optimum oxygen concentration levels for microaerophilic growth (6.5 to 114 µM).