AUXOSPORE FORMATION IN AN ANTARCTIC CLONE OF NITZSCHIA SUBCURVATA HASLE

Abstract

Several clones of an ice-related, planktonie diatom, forming chains with overlapping tips (as is typical in the section Pseudonitzschia), were isolated at Texas A&M University from a water sample collected a month earlier near McMurdo Sound, Antarctica, and later identified as Nitzschia subcurvata Hasle. After a week of log phase growth following the first transfer from a 5 ml microtest plate well in clone Mc-2, healthy, rapidly-growing cells clumped together in masses. Upon examination of the clumps, some free amoeboid-like cells were seen in fixed slides. The expanded auxospore had balloon-shaped walls, and the zygotes apparently developed into the elongate, banded perizonium (up to 92 μm) noted with complex organelles or the initial cells formed inside. The empty parent cells were ca. 52–58 μm in length, some vegetative cells were as small as 46 μm, while the newly formed, expanded cells were up to 92 μm long. Evidence of sexual reproduction has been little noted in marine planktonie Nitzschia species, although clumping has been recorded in the open ocean, and amoeboid bodies outside cells has been seen in coastal collections. Clumping is a growth habit commonly seen in stationary or senescent growth phases of cultures of related species such as Bacillaria paxillifer (O. F. Müller) Hendey as well as in other species in the section, e.g. Nitzschia pungens Grunow f. pungens and the neurotoxin producer Nitzschia pungens f. multiseries Hasle. Clone Mc-2 of Nitzschia subcurvata was tested for the possible production of the neurotoxic domoic acid in the senescent stage and tested negative.