Characterization of Germination of Desulfotomaculum nigrificans Spores ¹

Germination of spores of Desulfotomaculum nigrificans was studied by measuring reduction in numbers of heat-resistant units. Complete (>99.9%) germination was observed with heat-activated spores suspended in a combination of 1% soytone, 0.1% ferric citrate, 0.1% sodium metabisulfite (Na₂S₂O₅), and distilled water. In this medium spores germinated most rapidly at pH 6.0 - 8.0 when incubated at 55°C after the spores were exposed to a 15 - 20 min heat-shock at 100°C. Twelve amino acids triggered germination either together or individually only in the presence of ferric citrate and Na₂S₂O₅. No one amino acid as a germinant was superior to the others evaluated. Of nine carbohydrates examined (at 1% levels), fructose, ribose, and arabinose initiated germination individually in distilled water. Ferrous ion initiated germination whereas the ferric ion did not. Cu⁺⁺ (10mM) initiated germation whereas Zn⁺⁺ (10mM) inhibited germination. Phosphate buffer (67mM) and EDTA (10mM) inhibited cation-initiated germination. Reducing agents such as Na₂S₂O₅ may provide ferrous ions needed for spore germination. Ferrous ions as germinants indicate a possible significant role for an iron source when enumerating D. nigrificans spores or when evaluating food spoilage caused by D. nigrificans .