Effects of Toxic Substances on Natural Bacterial Assemblages Determined by Means of [ ³ H]Thymidine Incorporation

Abstract

The effects of 3,5-dichlorophenol, 2,4-dinitrophenol, and potassium dichromate on natural bacterial assemblages were examined by means of [ 3 H]thymidine incorporation into trichloroacetic acid-insoluble material. Results from a large number of coastal marine and freshwater samples suggest the following. (i) The effects of the three toxicants included reductions in the bacterial cell number as well as changes in rates of [ 3 H]thymidine incorporation and in [ 3 H]thymidine incorporation per cell. The concentrations that inhibited [ 3 H]thymidine incorporation by 50% ranged from 3 to 11 mg liter −1 for 3,5-dichlorophenol, 6 to 10 mg liter −1 for 2,4-dinitrophenol, and 21 to 123 mg liter −1 for potassium dichromate, with a tendency to higher values in bacterial assemblages from more eutrophic environments. (ii) The effects of 3,5-dichlorophenol and potassium dichromate determined by [ 3 H]leucine incorporation into bacterial protein were similar or larger than those obtained from [ 3 H]thymidine incorporation. (iii) Two to four hours of exposure to the toxicants was necessary before stable maximum effects were found in [ 3 H]thymidine incorporation. (iv) Storage of natural environmental samples should be avoided, since tests with water stored for 1 to 3 days sometimes produced results different from results obtained from in situ tests. (v) The effects of 3,5-dichlorophenol, 2,4-dinitrophenol, and potassium dichromate on natural bacterial assemblages were relatively constant during periods with different growth rates in the assemblages, during various periods of the year, and between samples from freshwater and marine localities. With some precautions, [ 3 H]thymidine incorporation can be used as a quick and sensitive method for determining the effects of toxicants on aquatic bacterial assemblages from natural environmental samples.

Tolerance (PICT) of the Bacterial Communities to Copper in Vineyards Soils from Spain

“…Thus, both techniques had equal potential for estimating metal tolerance of the bacterial community. This is consistent with studies on the effect of diverse toxic substances on bacterial assemblages from water (Riemann and Lindgaard‐Jörgensen, 1990; Tubbing, 1993). Likewise, similar IC 50 values were also reported for the two methods in a previous study performed with soil bacterial communities from an agricultural soil contaminated artificially in the laboratory (Díaz‐Raviña and Bååth, 1996b).…”

Sensitivity of Bacterioplankton in the Rhine River to Various Toxicants Measured by Thymidine Incorporation and Activity of Exoenzymes

“…Any interference of a toxicant with the cellular metabolism of heterotrophic bacteria would thus be detected. In accordance, Riemann and Lindgaard-Jorgensen [21] found recently that toxic effects on natural bacterial populations could be measured equally well with [3H]leucine incorporation into protein as well as t3H]thymidine incorporation into nucleic acids. Although thymidine incorporation is more sensitive to toxicants than enzyme activity ( [9,18] and this study), Obst et al [ 101 showed with the sensitivity of exoenzymes to heavy metals that exoenzymes could be successfully exploited for specific applications in ecotoxicological studies of water quality.…”

“…Bacterial communities in the Rhine River were relatively insensitive to additions of potassium dichromate, TPBS, and atrazine but showed specific differences in the shape of the dose-response curves. The unsensitivity of heterotrophic bacteria to additions of K2Cr207, indicated by EC5Os measured with thymidine incorporation ranging from 9.4 to 100 mg L-I, was also found by Riemann and Lindgaard-Jmgenson [21] in lakes and marine localities (EC50 thymidine incorporation 21 to 123 mg L-I); these concentrations are higher than the average concentration of total chromium of approximately 8 pg L-' in Rhine water in 1988 [24]. The strong influence of K,Cr207 on phosphatase activity in relation to protease activity could be caused by an interaction of chromate with phosphate through the cell membrane via the general anion transport [25].…”

Soil Microbial Community Response to Hexavalent Chromium in Planted and Unplanted Soil

“…A possible explanation for non‐development of Cr tolerance is that tolerance is widespread among soil microorganisms, and higher concentrations may be required to demonstrate such a difference (Giller et al, 1998). Riemann and Lindgaard‐Jørgensen (1990) exposed natural seawater and fresh water samples to a range of Cr(VI) concentrations and found IC 50 values ranging between 0.4 and 2.36 m M Viti and Giovanetti (2001), using vegetated tannery soil, found no difference in viable counts between control and Cr‐contaminated soil when low (0.15 m M ) Cr(VI) levels were added to the medium, but increased counts for the Cr‐contaminated sites at 1.5 m M Cr(VI). However, their soil could oxidize Cr(III) to (VI), thus longer term exposure might be needed, as shown for ammonia‐oxidizing bacteria (Gong et al, 2002), although in that case copper and arsenate were co‐contaminants in addition to Cr.…”