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Evaluation of the Most Probable Number Method for Enumerating Denitrifying Bacteria
Author(s) -
Davidson E. A.,
Strand M. K.,
Galloway L. F.
Publication year - 1985
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1985.03615995004900030023x
Subject(s) - denitrifying bacteria , enumeration , most probable number , incubation , soil water , population , denitrification , incubation period , biology , bacteria , environmental chemistry , chemistry , mathematics , ecology , nitrogen , biochemistry , demography , organic chemistry , combinatorics , sociology , genetics
Most probable number (MPN) enumerations of denitrifying bacteria were conducted on an agricultural soil (pH 6.6) and a forest soil (pH 5.6), in both neutral (pH 6.8) and acid (pH 5.6) media. The neutral medium yielded higher enumerations for both soils and, therefore, appears to be optimal, even for denitrifiers present in acid soils. Enzyme activity assays and MPN enumerations of seven soil samples were weakly correlated ( r = 0.71; p = 0.07). One soil exhibited a high MPN enumeration, but had no detectable denitrifying enzyme activity. While the enzyme assay indexes denitrification potential of soils under the environmental conditions at the time of sampling, the MPN enumeration indexes the denitrifying capability of the populations inhabiting soils. A population's denitrifying capability is related to its size, but other factors which might also influence MPN enumerations are discussed. Precise incubation time was critical in the MPN procedure. Delays of 2h affected the scoring results. Populations in some of the incubation tubes appeared to be in a dynamic growth phase at the end of the 14‐d incubation period. Inconsistencies in incubation duration could confound comparisons among soils. Despite inherent flaws and disadvantages, the MPN procedure may be appropriate for certain research objectives as an index of a population's denitrifying capacity. Recommendations and cautions are offered.