A PCR-MPN based quantitative approach to enumerate nitrifying bacteria in zeoponic substrates
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Self-sustaining, regenerative life-support systems are required for long-duration missions to the Moon and Mars. Improved activity of nitrifying bacteria to convert NH 4+ to NO 3- has been shown to promote plant growth in zeoponic substrates. Due to physiological characteristics, such as slow growth and low yield, nitrifying bacteria are not easily enumerated by traditional microbiological techniques. A method for rapid detection and enumeration of a commercial inoculum of nitrifying bacteria in a zeoponic substrate was developed using a polymerase chain reaction (PCR)-most probable number (MPN) approach. Samples from four-week laboratory incubation studies were processed to extract their total microbial community DNA and the sequences specific to 16s rRNA of Nitrobacter spp. were PCR amplified. The detection limit of the methodology was 2,000 Nitrobacter cells per assay. The quantitative assay demonstrated that the zeoponic substrate was capable of supporting 10 5 to 10 6 MPN Nitrobacter cells per gram of substrate. The PCR-MPN method can be an effective and rapid approach to enumerate nitrifying bacteria in zeoponic substrates.