Factors affecting the formation of spherical bodies in the spirochete Treponema denticola

The oral spirochete Treponema denticola typically is a helically shaped, motile bacterial cell. However, morphological variations of T. denticola cells in the form of "spherical bodies" are sometimes seen. Little is known about the environmental factors that cause their formation. The effects of oxygen, growth temperature, nutrient depletion and the addition of metabolic end-products were tested to determine their role in the morphogenesis of the spherical bodies. It was found that the age of the culture, the omission of individual components (yeast extract, rabbit serum, volatile fatty acids or thiamine pyrophosphate) from the medium and the addition of the metabolic end product lactic acid enhanced the formation of these bodies. However, their formation was decreased upon omission of the medium components asparagine and sodium bicarbonate.