Intracellular urease activity in the lichen Cladonia verticillaris, and its implication for toxicity.

Urea is currently used as a nitrogen fertilizer in many plant cultures, such as sugar cane. Several lichen species grow in the edges of the fields fertilized with urea. This implies that the hydrolysis of an excess of urea by soil bacteria or by the lichens themselves would increase the concentration of ammonia in the lichen thallus to a level that may be toxic to the photobiont. However, Cladonia verticillaris produces urease through positive feedback by urea supplied from the medium. This urease is partially secreted to the media or retained on the external surface of algal cells, as demonstrated herein by an adequate cytochemical reaction. This implies that ammonia produced by urea hydrolysis will be immediately dissolved in the water filling the intercellular spaces on the thallus. A possible protection mechanism against eventual ammonia toxicity, derived from the results described here, is also discussed.

Biochemical markers in taxonomy of the genus Cunninghamella.

The chemical composition of fatty acids and ubiquinones was studied in 18 strains of Cunninghamella, to establish quantitative and qualitative differences within the genus. Fatty acids analysis has shown the presence of four groups. Ubiquinone analysis, through high performance liquid chromatography (HPLC), demonstrated the existence of three different groups based on the ubiquinone type. The average percentage of fatty acids of the species Cunninghamella elegans and Cunninghamella bertholletiae, show variations in linolenic and stearic acids, suggesting the possibility of differentiation between the two species.