Sugar Acquisition during the Development of Microsporidian (Microspora: Nosematidae) Spores

Helicoverpa zea larvae were infected with Vairimorpha necatrix. The fat body was triturated and sporulation stages were fractionated according to buoyant density by Ludox density gradient centrifugation. Spores and sporulation stages formed two minor bands with buoyant densities of 1.072 and 1.121 g/ml, and two major bands with buoyant densities of 1.150 and 1.198 g/ml. The higher bands of less dense sporoblastic stages first appeared 96 hr following infection and the band containing the heaviest (1.198 g/ml) and most refringent mature spores appeared last, ca. 24 hr after the appearance of the other bands. Although the bands remained in the same relative positions regardless of the time after inoculation, the percentage of spores in Band 4 increased with time. The concentration of sugar in the spores from the 1.198-g/ml band was more than four times the concentration found in spores in the 1.150-g/ml band and accounted for more than 60% of the increase in spore weight between the two density classes. Similar tests with Nosema algerae yielded similar results, with sugars accounting for 88% of the increased spore weight. Sugar acquisition appears to occur during the attainment of the final spore density and perhaps signals spore maturation.