Moshe Shilo

Anaerobic heterotrophic dark metabolism in the cyanobacterium oscillatoria limnetica sulfur respiration and lactate fermentation

The cyanobacterium Oscillatoria limnetica, capable of anoxygenic photosynthesis in the light with sulfide as electron donor can anaerobically break down its intracellular polyglucose in the dark. In the absence of elemental sulfur, the organism carries out lactate fermentation; in its presence, anaerobic respiration occurs in which sulfur is reduced to sulfide. Induction of anoxygenic photosynthesis or synthesis of new proteins is not necessary for either process. Cells adapted in the dark to sulfur reduction are capable of anoxygenic photosynthesis during a subsequent light period, unless protein synthesis has been inhibited during the dark incubation period.

Isolation of “cyanophages” from freshwater ponds and their interaction with Plectonema boryanum

Abstract Viruses active against Plectonema boryanum (cyanophages) were isolated from freshwater ponds in Israel. On the basis of host specificity, DNA content, and fine structure, one of the viruses appears to be related or identical to the virus studied by Safferman and Morris (1963, 1964a), Schneider et al. (1964), and Smith et al. (1966a, b). The resistance of a mutant Plectonema strain to both viruses further strengthens this assumption. The anatomy of the cyanophages, their mode of attachment as revealed by electron microscopic examination, and the mechanism underlying resistance of the host Plectonema cell indicate a great similarity to the bacteriophages. The experiments also suggest that virus-induced lysis may provide a delicate means for study of the fine structure of susceptible algae, particularly the organization of the photosynthetic apparatus.

EFFECT OF PHOTOOXIDATIVE CONDITIONS ON LEVELS OF SUPEROXIDE DISMUTASE IN ANACYSTIS NIDULANS

In a recent report (Abeliovich and Shilo, 1972) “photooxidative death” in unicellular blue-green algae, among them Anacystis nidulans, was induced by incubation at both high (35°C) and low (415°C) temperatures under an atmosphere of oxygen and a medium devoid of CO,. When C 0 2 was added to the medium, photooxidative death was prevented only at the physiological temperature (35”C), indicating participation of some enzymatic activity in the process. A possible enzyme taking part in the prevention of photooxidative death is superoxide dismutase, which has been reported to play a key role in the protection of various aerobic organisms against the toxic effects of oxygen (McCord et al., 1971). Therefore, the activities of superoxide dismutase under normal growth conditions and under photooxidative conditions were tested and correlated with the physiological data in A . nidulans.

Procedure for purification and separation of Prymnesium parvum toxins

Abstract 1. 1. The procedure for purification and separation of Prymnesium parvum toxins as well as some studies on the chemical nature of the purified toxin are described. 2. 2. A highly purified Prymnesium parvum toxic principle was obtained using standard procedures for polar-lipids purification (column chromatography, differential solution and precipitation in solvent mixtures, and different partition between diphasic solvent mixtures). The toxic principle was purified 1500-fold with 50% yield. 3. 3. Using thin-layer chromatography the purified toxic principle was separated into as many as six components. 4. 4. Partial chemical analysis of the purified toxic principle showed 20.4% protein consisting of fifteen identified amino acids, a number of unidentified fatty acids, 0.47% phosphate, and 10–12% sugars.

Phormidium J-1 bioflocculant: production and activity

Phormidium J-1, a benthic filamentous cyanobacterium, isolated from a drainage channel, was found to produce a high molecular weight polymer. This substance can flocculate bentonite particles from suspensions. At the stationary phase of growth the cells excreted this bioflocculant into the surrounding medium. Production was enhanced by reduction of the calcium content in the growth medium or by increasing its EDTA content. Above the isoelectric point (pH 3.5) the bioflocculant is negatively charged. The presence of minimal concentrations of divalent cations in the reaction mixture is required for its flocculating activity. The production of bioflocculant could be of great importance in clarification of turbid water bodies, thus allowing light penetration to the sediment/water interface. Bioflocculant production and excretion was not found in several other benthic cyanobacteria.

STUDIES ON THE TOXIC PRINCIPLES FORMED BY THE CHRYSOMONAD PRYMINESIUM PARVUM CARTER

Prymnesium parvum, a phytoflagellate of the Chrysomonadineae widely distributed in sea water, rock pools, and estuaries (Carter, 1937; Droop, 1954), a t times produces extensive blooms in sheltered brackish water lagoons (Liebert and Deerns, 1920; Otterstrgm and Steemann-Nielsen, 1939). This massive growth of P. parvum has often resulted in mass mortality of fish populations, due to a soluble toxin formed by the phytoflagellate. In Israel, where the phytoflagellate first appeared in 1947 and then quickly spread throughout the couiitry, mass growths of Prymnesium have become a constant problem and danger in the fish-breeding industry. The future survival and expansion of carp-breeding in brackish water areas now largely depend on the successful control of P. parvum. Studies of ecology, factors determining toxin production, control measures, and nature of the toxins formed by the phytoflagellate are thus of great economic importance. Furthermore, the possibility of the spread of P. parvum to new, as yet uninfected regions, has been recently underlined by the appearance of blooms and fish mortalities in southeastern Europe (A. Valkanov, personal communication, 1960). With the present great increase of fish-breeding in brackish water ponds in Asian countries it is clear that Prymnesium infections may yet assume a much wider than local significance. In addition to the economic aspect of the study of Prymnesium, this organism presents a good model for studies of toxin formation in algae. I ts usefulness as a research tool rests on the facts that pure, axenic cultures have been obtained (Droop, 1954a; Reich and Kahn, 1954), and that its nutritional requirements are known and can be satisfied in a simple, fully-defined medium (Droop, 1954b; Mclaughlin, 1956; Rotberg, 1958). The isolation of products is thus not beset by the difficulties encountered with some other algae, such as Gymnodinium, whose pure culture growth is difficult and with which toxin producing contaminants have been encountered (RIyers et al., 1959). A special property of P. parvum, its great sensitivity to lysis by ammonia or acetic acid, makes it a suitable model for study of the penetration of weak electrolytes in nucleated cells (Shilo and Shilo, 1953; 1955; 1960).

Bacteriorhodopsin in a bloom of halobacteria in the Dead Sea

A dense bloom of red halobacteria developed in the Dead Sea in the summer 1980, bacterial densities of up to 1.9 x107 cells ml-1 were observed. The population consisted of two types: pleomorphic, cup-shaped cells and rod-shaped cells. A high content of bacteriorhodopsin was found in the bloom (up to 0.4 nmol per mg protein). The rod-shaped Halobacterium was isolated and was shown to contain bacteriorhodopsin.

Properties of marine bdellovibrios

Marine bdellovibrio isolates from the Israeli littoral of the Mediterranean Sea were screened and characterized in terms of host range, temperature and salinity ranges, cation requirement, mutation frequency, and G + C% mole content. Ten types of isolates were distinguished on the basis of these parameters.

The reproductive cycle of cyanophage LPP1-G in Plectonema boryanum and its dependence on photosynthetic and respiratory systems

Abstract The intracellular stages of the cyanophage LPP1-G reproductive cycle were established through mechanical burst of infected Plectonema cells. The stages consist of an initial eclipse period (3 hours), followed by intracellular maturation and, finally, lysis of the host cells with release of progeny at the end of the latent period. By excluding or inhibiting photosynthesis or respiration of the host, completion of the reproductive cycle at the maximal burst size (300–400 PFU/infected cell) was found to be dependent on photophosphorylation during the eclipse period. This photophosphorylation can be mediated by cyclic photophosphorylation. In the presence of respiration alone, the burst size is 8% of the maximal burst size and the duration of the cycle is greatly prolonged. The fact that the cyanophage can multiply in Plectonema boryanum without external carbon source is discussed.

The divalent cation requirement of Dead Sea halobacteria

Pleomorphic Halobacterium strains isolated from the Dead Sea (H. volcanii, H. marismortui) require high concentrations of divalent cations (75 mM Mg2+) for growth. When suspended in medium containing less than 50 mM Mg2+ cells lose their native shape within minutes and become spherical. This occurs even at elevated sodium chloride concentrations. Concomitant with the morphological changes, a high mlecular weight component which is positive in Coomassie Brilliant Blue and in periodate Schiff stain is released into the surrounding medium. At divalent cation concentrations lower than 100 mM magnesium cells were shown to lose their viability and their ability to incorporate amino acids. The potency of different divalent cations or their combinations to enable growth and stabilize morphology and viability was studied. It is suggested that different mechanisms underlie the divalent cation requirement of the different functions.