PYCNOCOCCUS PROVASOLII GEN. ET SP. NOV., A COCCOID PRASINOXANTHIN-CONTAINING PHYTOPLANKTER FROM THE WESTERN NORTH ATLANTIC AND GULF OF MEXICO1

The new genus Pycnococcus Guillard is based on several clones from the western North Atlantic and Gulf of Mexico. The type and only described species, Pycnococcus provasolii Guillard, sp. nov., is typified by clone Ω48-23 from the North Atlantic. Cells of Pycnococcus provasolii are solitary, spherical, 1.5–4.0 μm in diameter, have a resistant cell wall lacking sporopollenin, and have the ultrastructural characteristics of green algae. With the light microscope they are scarcely distinguishable from cells of other coccoid planktonic organisms. In pigmentation P. provasolii resembles Micromonas pusilla, Mantoniella squamata, and Mamiella gilva in having chl a, much chl b, Mg 2,4-divinylphaeoporphyrin a₅ monomethyl ester (presumably), and prasinoxanthin as a major xanthophyll. The pyrenoid of P. provasolii has a cytoplasmic channel, which is unique among species closely related to it. Flagellates, occurring rarely in culture, are similar to but distinguishable from known Pedinomonas species by size and shape. Pycnococcus provasolii is referred to the new family Pycnococcaceae Guillard, in the order Mamiellales of the class Micromonadophyceae (Chlorophyta). Clones of Pycnococcus provasolii are oceanic in nutritional characteristics, require only vitamin B₁₂ in culture, and are well adapted to growth under blue or blue-violet light of low intensity.     

THE RELATIONSHIP BETWEEN PSEUDOSCOURFIELDIA MARINA AND PYCNOCOCCUS PROVASOLII (PRASINOPHYCEAE, CHLOROPHYTA): EVIDENCE FROM 18S rDNA SEQUENCE DATA

18S rDNA sequences were obtained for the prasinophytes Pseudoscourfieldia marina (Throndsen) Manton and Pycnococcus provasolii Guillard. These sequences, along with those of additional prasinophytes and other green algae and land plants, were used for phylogenetic analyses by the neighbor-joining, maximum parsimony, and quartet puzzling methods. Results indicate that Ps. marina and Py. provasolii are closely allied and that both should be included in the Pycnococcaceae. In addition, results of these sequence analyses and additional pigment analysis indicate that the organism previously identified as Ps. marina, isolate CCMP 717, is, in fact, a Nephroselmis sp. or is closely related to that genus.     

PHOTOSYNTHETIC PIGMENTS OF PSEUDOSCOURFIELDIA MARINA AND SELECT GREEN FLAGELLATES AND COCCOID ULTRAPHYTOPLANKTON: IMPLICATIONS FOR THE SYSTEMATICS OF THE MICROMONADOPHYCEAE (CHLOROPHYTA)1

Photosynthetic pigments of the green flagellate Pseudoscourfieldia marina (Throndsen) Manton (Micromonadophyceae) are similar to those of the coccoid Pycnococcus provasolii Guillard; prasinoxanthin is the predominant carotenoid. Other organisms that possess prasinoxanthin also possess additional pigments not found in either P. marina or P. provasolii. Uriolide, a xanthophyll previously described from the coccoid done URI 266G, was also found in Mantoniella squamata (Manton et Parke) Desikachary, Micromonas pusilla Manton et Parke and Mamiella gilva (Parks et Rayns) Moestrup, all flagellate members of the Mamiellales, and the coccoid clone IV E5G. Other unidentified carotenoids were also present in M. squamata, M. pusilla, and M. gilva. These results suggest that P. marina and the coccoid organisms URI 266G and IV E5G may be related to the Mamiellales, and that P. provasolii may be more closely related to P. marina than to M. squamata, M. pusilla, and M. gilva.