Thymidine and leucine incorporation in soil bacteria with different cell size

Abstract

Thymidine and leucine incorporation into macromolecules of soil bacteria extracted by homogenization-centrifugation were measured after size-fractionation of the bacterial suspension through different sized filters (1.0, 0.8, 0.6, 0.4 μm). The specific thymidine incorporation rate was highest for the unfiltered and 1.0 μm filtered suspensions (approximately 10 × 10(-21) mol thymidine bacteria(-1) h(-1)), but decreased to 1.39 × 10(-21) mol bacteria(-1) h(-1) for bacteria passing the 0.4 μm filter. The proportion of culturable bacteria (percent colony forming units/acridine orange direct counts) also decreased with bacterial cell size from 5.0% for the unfiltered bacterial suspension to 0.8% in the 0.4 µm filtrate. A strong linear correlation (r (2) = 0.995) was found between the specific thymidine incorporation rate and the proportion of culturable bacteria. Leucine incorporation gave similar results to the thymidine incorporation. No effects of cell size on the degree of isotope dilution or unspecific labeling of other macromolecules were found either for the thymidine or the leucine incorporation technique. These data indicate that small bacteria, although more numerous than larger ones, not only constitute a smaller proportion of the soil bacterial biomass than larger bacteria, but also contribute to a lesser degree to carbon transformations in soil.

Linking bacterial community composition to soil salinity along environmental gradients

“…The used buffer concentrations did not affect bacterial Leu incorporation rates within the short time frame studied [30]. Following the adjustment of salinity or pH in the soil suspensions, bacterial growth was measured as the incorporation of 3 H-labeled leucine into bacterial protein [31, 32]. Briefly, 2 µl of radioactively labeled leucine, ([ 3 H]Leu, 185 MBq ml − 1 , 2 TBq mmol − 1 , Perkin Elmer) were added together with non-labeled leucine to the samples, resulting in a total concentration of 280 nM leucine.…”

The Effect of Clarithromycin Toxicity on the Growth of Bacterial Communities in Agricultural Soils

“…The bacterial community growth was estimated using the leucine incorporation technique [49,50]. Briefly, 1 g of soil (fresh weight) was mixed with 10 mL distilled water using a multivortex shaker at maximum intensity for 3 min, followed by low-speed centrifugation at 1000× g for 10 min to create a bacterial suspension in the supernatant.…”

Effect of Oxytetracycline and Chlortetracycline on Bacterial Community Growth in Agricultural Soils

“…The bacterial community growth was estimated using the leucine incorporation technique [19,20]. Briefly, 1 g of soil (fresh weight) was mixed with 10 mL of distilled water using a multivortex shaker at maximum intensity for 3 min, followed by low-speed centrifugation at 1000× g for 10 min, to create a bacterial suspension in the supernatant.…”