No abstract

Cyanobacterial mats of Solar Lake, studied in the field and by microscopic methods, arc classified into four types: flat shallow-water mat, pinnacle mat on the upper slope, cyanobacterial and other photosynthetic bacterial films on the lower slope, and flocculose mat at the bottom. The annual cycle and development of the four types are described.Mcasurements of photosynthesis by the flat shallow-water mat in the field and the laboratory yielded an average value of 10 g C mm2 d-'. In the flocculose anaerobic bottom mat 5 g C mm2 d-l was measured.Total accretion rates including organogenic material for the four mat types range between 5 and 50 cm 100 yr-I; aerobic and anaerobic degradation of the organic production of the shallow-water mat remineralizes more than 99% of the biomass. In the deeper parts of the mat, organic matter is transformed into carbonates. The role of bacteria in this process is demonstrated by ultramorphological analyses and by comparison to laboratory experiments with bacterial isolates.

Various axenic strains of Microcystis aeruginosa were found to have different short term toxic effects on Daphnia magna. One of these toxic manifestations, the "blocking" effect, markedly reduced the food uptake by the daphnids. In addition, several of the Microcystis strains are lethal for juvenile and adult daphnids. No correlations were found between the blocking of ingestion, lethality to daphnids, and the "mouse-killing" factors of Microcystis. Thus, several toxic principles are responsible for the different short term toxic manifestations.Microcystis aeruginosa is commonly involved in freshwater blooms. On many occasions such blooms have been followed by a mass poisoning of livestock and wild life (mammals and birds). These toxigenic blooms have been reported from many countries (Schwimmer and Schwimmer 1969; Carmichael 198 1;Codd 1984). Studies of Microcystis toxins have shown that more than a single toxic principle is involved (Foxall and Sasner 198 l), with different toxic manifestations (Codd and Carmichael 1982;Slatkin et al. 1983), different species specificities (Foxall and Sasner 198 l), various molecular weights (Runnegar and Falconer 198 l), and different amino acid composition (Santikarn et al. 1983).Increasing attention has been given to the relationship between M. aeruginosa and aquatic grazers such as Daphnia magna (Lampert 198 1, 1982

Quantitative methods were developed for the study of the early stages in the interaction of Bdellovibrio bacteriovorus and host bacteria. Attachment measurements were based on the differential filtration of host and parasite. Invasion was measured by estimation of radioactively labeled Bdellovibrio cells remaining attached to the host cells after mechanical agitation. The kinetics of attachment and the final number of Bdellovibrio cells attached were dependent on the multiplicity of the parasite, the composition and pH of the medium, and the incubation temperature. Inhibitors of Bdellovibrio motility, including chelating agents, NaN3, and low pH, all inhibited attachment, as did anaerobiosis. Ultraviolet-killed host cells retained their competence for attachment of Bdellovibrio cells, whereas heat-killed cells lost it. Invasion was selectively inhibited by inhibitors of protein synthesis, such as streptomycin, puromycin, and chloramphenicol. These antibiotics had no effect on attachment.

SUMMARYMethods of isolation and nutritional requirements of Bdellovibrio bacteriovorusstrains capable of growth on host-free media are described. Such strains retained their parasitic capacities for various Gram-negative bacteria after many transfers in host-free media. In parasite +host suspensions the spectrum of host specificity of various bdellovibrio strains was considerably wider than that obtained by examination for plaques on host lawns. The growth conditions therefore affect the capacity of the bdellovibrios to attach to and lyse host organisms. A proteolytic exoenzyme formed by certain bdellovibrio strains digested heat-killed, acid-treated or EDTA-treated host organisms, but did not affect intact host organisms. High phosphate concentrations inhibited exoenzyme activity. The morphological sequence of lysis induced by exoenzyme-forming parasitic bdellovibrio strains suggested that this lysis was a two-stage process: the first stage was specific attachment of bdellovibrios with damage to the cell wall of the host organisms ; the second stage was non-specific digestion of cellular components by exoenzyme produced by the bdellovibrios.