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M Shilo

Publications and source records attributed to M Shilo.

At least 19 recordsLinked to original sources
PubMed1976

Heterotrophic capacities of Plectonema boryanum.

Acquisition of the dark heterotrophic growth capacity on glucose in Plectonema boryanum involves both adaptation and enrichment of a fast-growing genotype. The adaptation includes induction of functions involved in glucose incorporation and increase in glucose-6-phosphate dehydrogenase activity. Photosynthetic products are implicated in the control of both systems. Efficient energy conversion in the dark, as measured by cyanophage multiplication, correlates in time with the increase in potential for glucose incorporation while heterotrophic growth capacity correlates with the increase in glucose-6-phosphate dehydrogenase activity. The lower efficiency of heterotrophic growth compared to photoautotrophic growth is discussed in light of the conservation of the photosynthetic potency in the heterotrophic cells.

Chlorophyll↗
PubMed1976

Metabolic aspects of LPP cyanophage replication in the cyanobacterium Plectonema boryanum.

Cyanophage LPP1G is reproduced at the same yield in heterotrophic conditions (dark, glucose) as in photoautotrophic conditions; aerobiosis is required for dark cyanophage replication. Exogenous glucose is not required for the cyanophage replication in the dark in heterotrophically grown cells. In photoautotrophically grown cells, the maximum burst size in dark and glucose is delayed for a period corresponding to glucose uptake induction. Cyanophage LPP2SPI replication occurs in conditions where only Photosystem I operates. Of photosynthesis parameters tested, only CO2 photoassimilation is affected during cyanophage LPP1G infection under photoautotrophic conditions.

Aerobiosis↗
PubMed1976

Photooxidation of cyanobacteria in natural conditions.

Photodynamic effects were demonstrated and assayed under field conditions in a number of different laboratory strains and pond isolates of cyanobacteria; parameters assayed for resistance to photooxidation were viable count, turbidity of the cyanobacterial suspension, and protein and pigment contents. The effects of density, colonial structure, and internal gas vacuoles on the lethal outcome were investigated. The stability and formation of superoxide dismutase under photooxidative conditions in the field and laboratory were studied in the different strains. An isolate of Microcystis from blooms in ponds exhibited extremely high resistance to photooxidation, which was abolished by exposure to chloramphenicol.

Cell Count↗
PubMed1975

Heterotrophic growth of the filamentous blue-green alga Plectonema boryanum.

Plectonema boryanum can grow in the dark with ribose, sucrose, mannitol, maltose, glucose, or fructose. Cell doubling times with 10 mM substrate are the following: 5 days with ribose, 6 days with sucrose or mannitol, 10 days with maltose, 12 days with glucose, and 13 days with fructose; with ribose plus 0.1% casamino acids it is 2.5 days. Dark-grown cells appear mophologically similar to light-grown cells. Cells grown in the dark for several years remain pigmented and resume photoautotrophic growth when placed in the light. Dim light (85 lux) increases the growth rate with ribose and with ribose plus casamino acids to nearly twice that of the dark rate. In the moderate light, growth takes place with ribose even in the presence of 1 times 10-5 MDCMU.

Culture Media↗
PubMed1975

Facultative anoxygenic photosynthesis in the cyanobacterium Oscillatoria limnetica.

An isolate from H2S-rich layers of the Solar Lake, the cyanobacterium Oscillatoria limnetica, exhibits both oxygenic and anoxygenic photosynthesis. It can use Na2S as an electron donor for CO2 photoassimilation (photosystem I supplies the energy) in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea or 700-nm light. A stoichiometric ratio of approximately 2 is observed between the Na2S consumed and the photoassimilated CO2. The anoxygenic phototrophic capability of this cyanobacterium explains its growth in nature in high sulfide concentrations and indicates a selective advantage.

Aerobiosis↗
PubMed1974

Growth cycle of predacious Bdellovibrios in a host-free extract system and some properties of the host extract.

Host-free growth and reproduction of a host-dependent strain of Bdellovibrio bacteriovorus incubated with an extract from host cells were studied. The morphological changes occurring in the cells were correlated with deoxyribonucleic acid (DNA) synthesis as measured by labeled nucleotide or orthophosphate incorporation. The host-free developmental cycle of Bdellovibrio is similar to that of the two-membered system; the early loss of flagella, the elongation into filaments, and multiple fission into flagellated progeny are typical for both host-free and intraperiplasmic development of bdellovibrios. Filament length and time of division appear to depend on the concentration of the host extract. Host extract was found to be heat stable and DNase stable, and Pronase sensitive and RNase sensitive. Addition of ribonucleic acid to the extract medium at various times during the Bdellovibrio growth cycle demonstrated that host extract is required continuously during the cycle for growth. The observations reported give a unified picture of Bdellovibrio development and allow for the suggestion that wild-type bdellovibrios depend upon the presence of some host factor for induction of DNA synthesis, whereas depletion of host factor triggers division. The ecological implications of such host dependence are discussed.

Bacteria↗
PubMed1972

Photooxidative death in blue-green algae.

When incubated in the light under 100% oxygen, wild-type blue-green algae (Anacystis nidulans, Synechococcus cedrorum) die out rapidly at temperatures of 4 to 15 C, and at 35 C (or at 26 C in the case of S. cedrorum) in the absence of CO(2). Photosynthesis is impaired in these cells long before they die. Blocking of photosystem II at high temperatures in the presence of CO(2) sensitizes the algae to photooxidative death. Photooxidative death and bleaching of photosynthetic pigments are separable phenomena. Photooxidative conditions were demonstrated in Israeli fish ponds using A. nidulans as the test organism during dense summer blooms, when dissolved CO(2) is low, and in winter, when water temperatures generally drop below 15 C. This finding suggests that photooxidative death may be responsible for the sudden decomposition of blue-green blooms in summer, and may be a factor in the absence of blue-green blooms in winter.

Cyanobacteria↗
PubMed1972

Toxigenic algae.

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Animals↗
PubMed1971

Endogenous dark respiration of the blue-green alga, Plectonema boryanum.

Endogenous dark respiration in the blue-green alga Plectonema boryanum is markedly affected by preincubation in the light: it can be increased from a basal rate of 5 nmoles of O(2) to 55 nmoles of O(2) per mg of cell protein per min after exposure of the cells to light for 8 to 10 hr. Under conditions of enhanced dark respiration, cyanophage multiplication in the dark increases drastically and approaches the cyanophage yields obtained in photosynthesizing Plectonema cells. This implies that the biosynthetic capabilities of the algal cells, at least with respect to viral synthesis, can be similar in the dark to those in the light. The enhanced endogenous respiration rate was found to be dependent on photoassimilation of CO(2) and on protein synthesis. The implications of these findings with respect to obligate photoautotrophic metabolism in blue-green algae are discussed.

Carbon Dioxide↗