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Fifteen host-range (h) mutants of cyanophage N-1 were characterized with reference to their efficiency of plating, time of appearance, morphology and size of plaques on Nostoc muscorum and its three phage-resistant (Nm 1/N-1, Nm 2/N-1 and Nm 8/N-1) mutants. While phage N-1 did not adsorb to the three phage-resistant mutants, the h mutants differed one from the other in having lower or higher adsorption rate constants on N. muscorum or the phage-resistant mutants. The inability of majority of h mutants isolated on Nm 1/N-1 to grow in Nm 8/N-1 was shown to be due to a failure of adsorption. The h mutants also differed one from the other in their reversion (back mutation) frequencies. The lethal doses (LD37) required to kill 37% of free phage particles after UV-irradiation, heating and ethylenediamine tetraacetate (EDTA) treatment greatly varied. Most of the h mutants were found to be considerably more sensitive to UV and thermic inactivation than N-1 while they were resistant to EDTA. The h mutants except five of them were unable to multiply at 40 degrees C. The significance of these features is discussed.

The effect of temperature, ultraviolet (UV) light and ethylenediaminetetraacetic acid (EDTA) on the stability of cyanophage N-1, infecting the cyanobacterium Nostoc muscorum was studied. Complete inactivation of the phage occurred at 60 degrees C in 6 mins. All the temperature-sensitive (ts) mutants exhibited faster inactivation at 50 degrees C than the wild type. UV light readily inactivated the particles of the wild giving a survival of 3.44% at a dose of 60 secs. All the ts-mutants were found to be more sensitive to UV light than the wild type. 10(-4) mol/l EDTA inactivated 40% of the wild type in 60 mins. 5 x 10(-4) mol/l EDTA inactivated the wild type nearly completely within 2 mins, while a similar inactivation of ts-mutants required only 90 secs.

Optimal conditions for the induction of host-range mutants of cyanophage N-1 by acridine orange were established. Induced host-range mutants were isolated with a frequency of 0.1 to 4.0 x 10(-5) over a spontaneous mutation frequency of 0.2-3.6 x 10(-11).

Inorganic nitrogens sources like nitrate, nitrite enhanced sporulation and glycogen accumulation in Anabaena sp. but ammonium chloride neither influenced sporulation nor glycogen accumulation. Acetate and citrate also stimulated early sporulation and glycogen level was higher over nitrogen free control. Nitrogen and carbon sources in combination proved to be useful in inducing early sporulation and increased content of glycogen. Phosphate and calcium also affected glycogen accumulation significantly, although, the sporulation was found to be of the same order as in nitrogen free medium. Sulphate initiated early sporulation, the mechanism of which is not known.

Glycogen accumulation in vegetative cells of Anabaena sp. is demonstrated to be a light-dependent process. No glycogen accumulation is found in dark or in cultures supplemented with 10(-5) M DCMU in light. Large quantities of glycogen accumulate in cells undergoing sporulation and the amount increased with the onset of maturation of spores.

The effect of 21 amino acids was studied on glycogen accumulation during sporulation in the blue-green alga Anabaena sp. All the amino acids enhanced the initial level of glycogen on the 4th day. The maximum amount of glycogen, on the 20th day, was noticed from L-methionine, L-tyrosine, glycine, and L-histidine supplemented cultures. Others like L-serine, L-valine, L-asparagine, DL-alanine, L-glutamic acid, L-phenylalanine, L-aspartic acid, L-arginine, and DL-lysine come next in the order. On the other hand, L-cysteine and L-cystine, although upto the the 16th day they exhibited higher values of glycogen, did not show much variation in glycogen content over nitrogen-free medium. Except in these two amino acids, in all others initiation of sporulation occurred on the 4th day, resulting in free spores on the 8th day. But in case of L-serine, L-asparagine, L-isoleucine, and L-phenylalanine free spores were noticed only on the 12th day while in DL-lysine they were seen on the 16th day. L-cysteine and L-cystine supplemented media showed free spores on the 20th day as in nitrogen-free control.