Widespread occurrence of the oceanic ultraplankter, Prasinococcus capsulatus (Prasinophyceae), the diagnostic "Golgi-decapore complex" and the newly described polysaccharide "capsulan"'

A nonmotile green nanoalga was isolated from the waters over the Cayman Tre nch in March 1979 and has been maintained in culture as done URI 266G (CCMP 1202). It was observed to form a copious polysaccharide capsule that presu mably originated in the Golgi body and was secreted through a crown of 10 p ores in the cell wall, the "decapore." This multilaminate apical area, lyin g adjacent to the Golgi, underwent structural changes during morphogenesis. The polysaccharide precursors that coalesced to form the capsule apparentl y became stainable and visible as they exited the decapore when they cross- linked with divalent ions in seawater. Cell wall precursors, or a cell wall lamina, surrounded the daughter cells both during synchronous binary fissi on and after cell separation, with the maternal capsule perhaps acting as a template. Similar prasinophyte isolates have been obtained from widespread areas of the North Atlantic and were divided into two subgroups on the bas is of their pigment complement (Hooks et al. 1988). One subgroup, typified by clone Omega 48-23 (CCMP 1203), was described by Guillard et al. (1991) a s Pycnococcus provasolii Guillard within a new family, the Pycnococcaceae. The other subgroup, typified by done URI 266G (CCMP 1202), contained two un ique carotenoids, one of which was uriolide (Foss et al. 1986). Subsequentl y, Miyashita et al. (1993) described an alga from the western Pacific Ocean that is indistinguishable from URI 266G in both pigment composition and ul trastructure that they named Prasinococcus capsulatus Miyashita et Chihara and placed tentatively in the Pycnococcaceae. They described a curious asex ual budding fission. Here we suggest an alternative form of cell division a nalogous to that observed in the other described Pycnococcaceae. We used th e ultrastructure of cells in exponential and stationary phases of growth to illustrate synchronous asexual binary fission, the "Golgi-decapore complex ," and its apparent role in capsule formation. A unique sulfated and carbox ylated polyanionic polysaccharide named capsulan is released from this comp lex.