The use of fluorescein isothiocyanate in the determination of the bacterial biomass of grassland soil

Abstract

Quantitative recoveries of bacteria added to a number of soils were obtained using fluorescein isothiocyanate (FITC) as a stain. Enzyme fluorescence, using fluorescein diacetate or dibutyrate, could not be adapted for the routine counting of metabolizing organisms in soil. Staining with rose bengal gave recoveries of 60–80%.Soil-extract dilution plates revealed 4 × 107 bacteria/g in the 0–10 cm layer in April and 27 × 107 in October. One-third of this number was observed in the 20–30 cm layer. Actinomycete colonies added another 20% to the counts at the 0–30 cm depth but constituted 70% of the total colonies from the 90–120 cm depth. Microscopic counts indicated 2.2–4.6 × 109 organisms/g of surface soil. The number of bacteria decreased in a linear fashion with depth but no relation was found between the numbers obtained by direct microscopy and those by plate counting. However, each of the methods showed a high relationship between the size of the bacterial population present at each depth on the different sampling dates.The observed bacteria, actinomycete spores, and hyphal segments averaged 0.6 × 1 μ. On this basis, the biomass in the top 30 cm, as determined by direct microscopy, ranged from 30 to 76 g/m2 (dry weight basis). This implies, considering the amount of available energy, that the individual cells have enough energy to divide only a few times each year. Direct microscopic counting yields a quantitative picture of the organisms present but cannot separate between inactive cells, spores, and metabolizing organisms. Data from plate counts probably give a truer indication of metabolically active cells.

Effects of Spartina alterniflora invasion on benthic nematode communities in the Yangtze Estuary

“…Each of the composite sediment samples was well homogenized by hand and then split into 4 parts: 150 g of sediment were fixed in 4% formalin for nematode community analysis, 50 g of sediment were used for measurement of bacterial biomass, 100 g were dried to constant weight at 80°C to determine water content, and the rest of each sub-sample was air-dried and analyzed for physical and chemical properties, including organic matter, pH, electrical conductivity, total nitrogen, total phosphorus (measured at the Institute of Soil Science, Chinese Academy of Sciences), and sediment grain composition (measured at the Cold and Arid Environmental and Engineering Research Institute, Chinese Academy of Sciences). The biomass of sedimentary bacteria was determined by counting bacteria stained with fluoroscein isothiocyanate (FITC) by direct microscopic observation (Babiuk & Paul 1970). Standing shoots of plants were harvested in two 25 × 25 cm quadrats along each transect, for the determination of shoot biomass.…”

Effects of Atmospheric CO2 Enrichment on the Growth and Mineral Nutrition of Quercus alba Seedlings in Nutrient-Poor Soil

“…Interference from stained clay particles and organic matter probably led to a uniform overestimation of bacterial populations in all treatments. In the second harvest, bacteria in 100-MAl aliquots of the original 10-2 dilution were stained with fluorescein isothiocyanate (1), and very little interference was encountered. The filters were mounted on slides and examined under a Nikon Fluophot epifluorescence microscope.…”

Effect of Labile Inorganic Phosphate Status and Organic Carbon Additions on the Microbial Uptake of Phosphorus in Soils

“…This investigation had the objectives of (a) measuring the change in P forms (labile P1 and P,,) (Babiuk and Paul 1970) by a factor of 3.63.…”