THE SUGAR CONTENT AND DENSITY OF LIVING AND DEAD MICROSPORIDIAN (PROTOZOA, MICROSPORA) SPORES

Microsporidian (Microspora) spores were subjected to several kinds of stress: ultraviolet light (Nosema al gerae); chilling in ice water (Ed hazardia aedis); freezing and thawing, with or without glycerol as a c ryoprotectant (Nosema disstriae, Thelohania sp.); longterm cold storag e (Vairimorpha spp., Endoreticulatus sp., Thelohania sp., and Microspo ridium sp.); and extended periods at room temperature (Microsporidium sp. and Vairimorpha lymantriae). N. algerae spores were inactivated by incubation in 0.05 M NaCl or 24 hr at 23 degrees C. Viability of the spores was assessed either by infectivity to a susceptible host or by in vitro germination. Carbohydrates were extracted from the spores for measurement of the total sugars (anthrone reactive) and reducing suga rs (Nelson's test), and quantities and ratios of the two classes of su gars were com pared. Buoyant density differences associated with sugar concentration and viability changes were estimated by Ludox density g radient centrifugation. Reducing sugar levels increased after germicid al ultraviolet radiation, chilling, or freezing, concurrent with loss of infectivity or capacity for germination. The smaller reducing sugar molecules apparently diffused slowly from the inviable spores, causin g a gradual reduction in the total concentration of sugars. Many sampl es of spores held for long periods in cold storage were almost devoid of sugar, These changes were not seen in N. algerae spores that were t emporarily inactivated. In all cases, spores that were severely deplet ed in carbohydrates had a significantly lower buoyant density. The ban ds of heavy spores had a mean density +/- SE of 1.197 +/- 0.010 g/ml a nd the mean density of the light, sugar-depleted spores was 1.137 +/- 0.024 g/ml. These results suggest that, where no other means are possi ble, sugar concentrations or spore density might be used to assess the viability of spores. (C) 1996 Academic Press, Inc.