Many cyanobacteria produce peptides that inhibit mammalian proteases. The hypothesis that inhibitors of mammalian proteases produced by cyanobacteria also interfere with digestive proteases of natural cladoceran grazers was tested by comparing the effects of cyanobacterial protease inhibitors on digestive proteases from Daphnia magna and on commercially available bovine proteases. The major digestive proteases of D. magna are trypsins and chymotrypsins, which differ from those of bovine origin in substrate specificity and susceptibility to synthetic inhibitors. An extract from Microcystis aeruginosa strain PCC 7806 inhibited both types of D. magna proteases. Subsequent fractionation of the extract by high-performance liquid chromatography indicated that several inhibitors are produced by M. aeruginosa that differ in their specificity for the trypsins and chymotrypsins of D. magna. Two fractions differed in their inhibitory effect on proteases of D. magna and bovine origin; therefore, assessment of the impact of cyanobacterial protease inhibitors on natural communities requires the use of digestive proteases from ecologically relevant grazers.

Nostoc is a complex and tough genus to differentiate, and its morphological plasticity makes it taxonomically complicated. Its cryptic diversity and almost no distinguishable morphological characteristics make this genus incredibly heterogeneous to evaluate on taxonomic scales. The strain NOS, isolated from a eutrophic water body, is being described as a new genus Aliinostoc with the strain showing motile hormogonia with gas vesicles as an atypical feature, which is currently considered as the diacritical feature of the genus but should be subjected to critical evaluation in the near future. The phylogenetic placement of Aliinostoc along with some other related sequences of Nostoc clearly separated this clade from Nostoc sensu stricto with high bootstrap support and robust topology in all the methods tested, thus providing strong proof of the taxa being representative of a new genus which morphologically appears to be Nostoc-like. Subsequent phylogenetic assessment using the rbcL, psbA, rpoC1 and tufA genes was done with the aim of facilitating future multi-locus studies on the proposed genus for better taxonomic clarity and resolution. Folding of the 16S-23S internal transcribed spacer region and subsequent comparisons with members of the genera Nostoc, Anabaena, Aulosira, Cylindrospermum, Sphaerospermopsis, Raphidiopsis, Desmonostoc and Mojavia gave entirely new secondary structures for the D1-D1' and box-B helix. Clear and separate clustering from Nostoc sensu stricto supports the establishment of Aliinostoc gen. nov. with the type species being Aliinostoc morphoplasticum sp. nov. in accordance with the International Code of Nomenclature for algae, fungi and plants.

Summary• The change in algicide synthesis in response to nutrients and pH in axenic cultures of the planktonic cyanobacterium, Oscillatoria laetevirens is reported.• Analytical and bioassay techniques were used to determine the effects of nitrogen (N), sulpher (S), phosphorus (P), magnesium (Mg 2+ ), calcium (Ca 2+ ) and hydrogen (H + ) on Oscillatoria laetevirens growth, secondary metabolite accumulation and minimum inhibitory concentration in culture filtrates.• Growth and secondary metabolite production were affected by nutrient addition. High algicide production, which was not dependent on optimal growth, correlated with deficiences of magnesium and phosphate, and high pH. Algicidal activity in the culture medium was not detected following organic nitrogen addition while optimal growth was sustained; however, ammonia reduced biomass yield but did not affect algicide formation. The differential algicide concentration inside the cells and in the culture medium indicated secretion by an efflux mechanism rather than leakage from aging cells.• Algicide production by Oscillatoria laetevirens was negatively regulated by both phosphate and magnesium, and by pH. The interactive influence of nutrients and allelopathy is discussed in species succession and dominance in the maintenance of freshwater blooms.

An isolate of Oscillatoria from local eutrophic lake exhibits strong growth inhibitory effects, when phototrophically co-cultured with a green alga and other blue-green algae, including its natural predecessor. This effect was not observed on selected heterotrophic-organisms. The characteristic interaction was also demonstrated with culture filtrates and cell-free extracts, implying this effect to be due to some chemical released from Oscillaroriu. From the mid-log growth phase of the culture, a nonproteinaceous, moderately heat stable, and ether soluble metabolite was extracted by ether extraction. The primary site of the growth inhibitory substance (algicide) action appears-to be the photosynthetic oxygen evolution, tested in Anacystis nidulans.Algal bloom sequence in eutrophic freshwater lakes, is usually determined by several interacting factors, which include light and major nutrients (KLEIN and CRONQUIST 1967, SHAPIRO 1970). Consequently, the effects of extracellular metabolites (allelopathy, probiosis and antibiosis) have been suggested as playing major role in sequence determination within a phytoplankton population (KEATING 1977).A wide range of blue-green algae (cyanobacteria) exert inhibitory effects on growth of other algal species, and this interaction has often been attributed t o the extracellular metabolites, namely polysaccharides (and bacteriocin like proteins (FLORES and WOLK 1986).However, our knowledge t o the algicidal function of blue-green algae is, as yet, restricted to one species, Scytonenza lioffmunii (MASON et ul. 1982), whose functional metabolite has been well characterized (GLEASON et ul. 1986, GLEASON and PAULSON 1984, GLEASON and BAXA 1986, PIGNATELLO et ul. 1983.

No abstract

No abstract

In this article we describe the partial characterization of a Synechococcus sp. PCC 7942 mutant Mu1 with an enhanced resistance towards the herbicide bentazone (3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one 2,2-dioxide). The mutant was derived from a random mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (NSG) and exhibited superior growth rates, pigment content and overall photosynthetic activities under regular growth conditions compared to wild type. Whereas Synechococcus PCC 7942 wild type showed significant photoinhibition, especially in the presence of lincomycin, Mu1 was much more robust. A comparative analysis of the content of several photosynthesis-associated proteins revealed that Mu1 had an increased expression of PsbO on mRNA and protein level and that PsbO is tightly bound to Photosystem II, relative to wild type. This result was substantiated by mass spectrometer measurements of photosynthetic water oxidation revealing a higher stability and integrity of the water oxidizing complex in Mu1 cells grown under regular or calcium deficient conditions. Therefore, our results give rise to the possibility that the overexpression of PsbO in mutant Mu1 confers resistance to reactive oxygen species (ROS) formed as a consequence of bentazone binding to the acceptor side of PS II. In addition, we observed a significantly higher tolerance towards bentazone in iron depleted wild type cells, conditions under which the IdiA protein becomes expressed in highly elevated amounts. As we have previously shown, IdiA preferentially protects the acceptor site of PS II against oxidative stress, especially under iron limitation. Thus, it is likely that IdiA due to its topology interferes with bentazone binding or protects PS II against ROS generated in the presence of bentazone.

SUMM.^RYWhen cultured with an axenic pianktonic Oscillatoria sp., growth of some cyanobacteria and a green alga was suppressed owing to release of an algicidal metabolite (antibiotic). Growth inhibition was also detected on exposure to a cell-free extract of Oscillatoria or to an ether extract. The ether extract abolished tbe photosystem (PS) II activity of Anacystis nidulans. Experimentation with a combination of photosynthetic electron acceptor-donor systems indicated that the antibiotic also inhibited PS II in isolated chloroplasts, primarily interacting at a site before P680 on the electron transport chain. The cyanobacterial product also suppressed growth of some natural isolates of cyanobacteria and green algae in controlled conditions and decreased the population density of a green alga (phytoplankton) in nature. Growth of higher plants was also affected, though only wben the Oscillatoria extract was applied to leaves. Experinnental mice were unaffected by the antibiotic. Upon thin layer chromatography of the ether extract, two fractions witb algicidal activity fluoresced under ultraviolet light. Long-cbain saturated fatty acids were the major components of the fractions. The suitability of the antibiotic in control of toxic algae is discussed.