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Vibrio cholerae serogroup O1, the causative agent of cholera, is capable of surviving in aquatic environments for extended periods and is considered an autochthonous species in estuarine and brackish waters. These environments contain numerous elements that may affect its ecology. The studies reported here examined physical interactions between V. cholerae O1 and natural plankton populations of a geographical region in Bangladesh where cholera is an endemic disease. Results showed that four of five clinical V. cholerae O1 strains and endogenous bacterial flora were attached preferentially to zooplankton molts (exuviae) rather than to whole specimens. One strain attached in approximately equal numbers to both exuviae and whole specimens. V. cholerae O1 also attached to several phytoplankton species. The results show that V. cholerae O1 can bind to diverse plankton species collected from an area where cholera is an endemic disease, with potentially significant effects on its ecology.

The rapid, specific effects of 25 fluorochromes at low concentration and physiological conditions of pH and temperature were investigated on live cells of five phytoplankton species (Prorocentrum micans, Amphidinium carterae, Dunaliella tertiolecta, Chlamydomonas moewusii and Fragilaria crotonensis). They allowed the identification of cellular components such as the plasma membrane, endoplasmic reticulum, Golgi apparatus, thecal plates, nucleus, mitochondria, trichocysts, vacuoles/lysosomes, polyphosphate and starch granules, lipid bodies and hydrolytic enzymes. Morphological alterations of some of these constituents were examined in cells at different metabolic states. It was found that the thickness of Prorocentrum thecal plates increases during cell development while surface pores appear to be formed in the early stages of thecal formation. The number and size of mitochondria varies among cells at different stages of growth. The number of trichocysts, the size of vacuoles and the quantity of polyphosphates, starch or lipid inclusions increases in nitrogen-depleted cells. Photodegradation and photoenhancement phenomena are described. Some important factors helping to avoid quenching and some applications of the fluorochroming technique are presented.

The spindle in dividing cells of the diatom Stephanopyxis turris contains three distinct classes of microtubules: central spindle microtubules, which slide over each other and grow during anaphase spindle elongation; kinetochore-attached microtubules, which are located on the outer surface of the central spindle; and peripheral microtubules, which fan out from the spindle poles in astral-like arrays. The poles are multilayered structures, which remain attached to the spindle after isolation. In vitro, after addition of ATP, central spindles elongate and the two half-spindles slide completely apart with a concurrent decrease in the extent and magnitude of the zone of microtubule overlap. Spindle elongation takes place in spindles whose chromatin has been removed by enzymic digestion and the extent of elongation in vitro is increased by the addition of neurotubulin. After ATP addition the arrays of interdigitating microtubules in the zone of overlap become disordered and selectively depolymerize from the overlap zone polewards. In some reactivated spindles an unusual structure, a striated fibre, can be seen running from the pole plates part of the way towards the spindle midzone. The fibre has no precedent in mitotic ultrastructure and its function is unclear. These results demonstrate that we can duplicate the essential elements of anaphase B in vitro and that this system will be useful for further studies of the molecular basis of spindle elongation.