DETECTION AND COUNTING OF NITROBACTER POPULATIONS IN SOIL BY PCR

Although the biological conversion of nitrite to nitrate is a well-kno wn process, studies of Nitrobacter populations are hindered by their p hysiological characteristics, This report describes a new method for d etecting and counting Nitrobacter populations in situ with the PCR. Tw o primers from the 16S rRNA gene were used to generate a 397-bp fragme nt by amplification of Nitrobacter species DNA, No signal was detected from their phylogenetic neighbors or the common soil bacteria tested, Extraction and purification steps were optimized for minimal loss and maximal purity of soil DNA, The detection threshold and accuracy of t he molecular method were determined from soil inoculated with 10, 10(2 ), or 10(3) Nitrobacter hamburgensis cells per g of soil. Counts were also:done by the most-probable-number (MPN)-Griess and fluorescent ant ibody methods. PCR had a lower detection threshold (10(2) Nitrobacter cells per g of soil) than did the MPN-Griess or fluorescent antibody m ethod, When PCR amplification was coupled with the MPN method, the cou nting rate reached 65 to 72% of inoculated Nitrobacter cells, Tested o n nonsterile soil, this rapid procedure was proved efficient.