Photoreactivation of UV-irradiated blue-green algal virus LPP-1

UV-inducible DNA repair in the cyanobacteria Anabaena spp

Strains of the filamentous cyanobacteria Anabaena spp. were capable of very efficient photoreactivation of UV irradiation-induced damage to DNA. Cells were resistant to several hundred joules of UV irradiation per square meter under conditions that allowed photoreactivation, and they also photoreactivated UV-damaged cyanophage efficiently. Reactivation of UV-irradiated cyanophage (Weigle reactivation) also occurred; UV irradiation of host cells greatly enhanced the plaque-forming ability of irradiated phage under nonphotoreactivating conditions. Postirradiation incubation of the host cells under conditions that allowed photoreactivation abolished the ability of the cells to perform Weigle reactivation of cyanophage N-1. Mitomycin C also induced Weigle reactivation of cyanophage N-1, but nalidixic acid did not. The inducible repair system (defined as the ability to perform Weigle reactivation of cyanophages) was relatively slow and inefficient compared with photoreactivation.

Photoreactivation of ultraviolet irradiated blue-green alga: Anacystis nidulans and cyanophage AS-1

Ultraviolet (UV) inactivation and photoreactivation of Anacystis nidulans and cyanophage AS-1 was studied at different wavelengths. UV inactivation of free phage particles and one and two hour host-phage complexes (intracellular phages) were exponential. UV resistance of plaque forming units was attained at the latter phase of latent period. Black, blue and white lights were able to photoreactivate the UV irradiated A. nidulans whereas green, yellow and red lights were not. However, incubation of A. nidulans for more than 2 hours in black light resulted in loss of viability but shift to red light caused significant recovery. This suggests the involvement of two types of photoreactivation, i.e. of photoenzymatic repair of DNA and of the repair of the photosynthetic apparatus of A. nidulans.

Mutagenesis of free and intracellular cyanophage AS-1 by ultraviolet, N-methanyl-N'-nitro-N-nitrosoguanidine and acriflavine

Mutagenic actions of ultraviolet irradiation (UV), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and acriflavine (photodynamic) were tested in free and intracellular phage AS-1 infecting Anacystis nidulans IU625. Spontaneous and induced mutations with particular reference to host range (h) and minute plaque formation (m) were investigated. The spontaneous mutation frequencies varied from 10(-9) to 10(-8) and from 2 X 10(-5) to 2 X 10(-4) for h and m mutants respectively. UV was efficient in inducing h and m markers in free phage particles as well as intracellular phage; MNNG induced both markers in intracellular phage only, and acriflavine induced m mutants only in free as well as in infecting phages. UV-induced mutations in free phage were photo-reactivable by visible light. With all the mutagens used, maximal induction of both markers was observed with treatment of 2-h complexes.

Ultraviolet light-induction and photoreactivation of thymine dimers in a cyanobacterium, Anacystis nidulans

Partially photoreactivable mutant of Anacystis nidulans demonstrates partial photorepair of thymine dimers. The wild type which is completely photoreactivable at the conditions studied shows higher level of thymine dimer photolysis.

Ultraviolet light inactivation and photoreactivation of AS-1 cyanophage in Anacystis nidulans

Black light effected photorecovery of AS-1 cyanophage and wild-type cells. However, only partial photoreactivation of AS-1 was observed in a partially photoreactivable mutant of Anacystis nidulans.

Photoreactivation of UV-irradiated blue-green algae and algal virus LPP-1

Ultraviolet (UV) sensitivity and photoreactivation of blue-green algae Cylindrospermum sp., Plectonema boryanum, spores of Fischerella muscicola and algal virus (cyanophage) LPP-1 were studied. The survival value after UV irradiation of filaments of Cylindrospermum sp. and Virus LPP-1 showed exponential trend and these were comparatively sensitive towards UV than F.muscicola and P.boryanum. Photoreactivation of UV-induced damage occurred in black, blue, green, yellow, red and white light in Cylindrospermum sp., however only black, blue and white light were capable of photorepair of UV-induced damage in P.boryanum, spores of F.muscicola and virus LPP-1 in infected host alga. Pre-exposure to yellow and black light did not show photoprotection. The non-heterocystous and nitrogen fixation-less mutants of Cylindrospermum sp. were not induced by UV and their spontaneous mutation frequency was not affected after photoreactivation. The short trichome mutants of P.boryanum were more resistant towards UV. The occurrence of photoreactivation of UV-induced killing wide range of light in Cylindrospermum sp. is the first report in organisms.

Cyanophages-viruses attacking blue-green algae

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Isolation and characterization of ultraviolet light-sensitive mutants of the blue-green alga Anacystis nidulans

Three independently isolated ultraviolet light-sensitive (uvs) mutants of Anacystis nidulans were characterized. Strain uvs-1 was most sensitive to UV in the absence of photoreactivation. Pretreatment with caffeine suppressed the dark-survival curve of strain uvs-1, indicating the presence of excision enzymes involved in dark repair. Under "black" and "white" illumination, strain uvs-1 displays photoreactivation properties nearly comparable to wild-type culture. Mutants uvs-35 and uvs-88 appeared to have partial photorecovery capacities. Upon pretreatment with chloramphenicol, photoreactivation properties of strains uvs-1 and uvs-88 were not evident although the partial photoreactivation characteristics of strain uvs-35 remained the same. Data indicate that strains uvs-1, uvs-35, and uvs-88 are probably genetically distinct UV-sensitive mutants.

LPP-1 infection of the blue-green alga Plectonema boryanum. II. Viral deoxyribonucleic acid synthesis and host deoxyribonucleic acid breakdown

Host and viral deoxyribonucleic acid (DNA) metabolism in LPP-1-infected Plectonema boryanum was studied by equilibrium centrifugation in CsCl gradients. Approximately 50% of the host DNA is degraded to acid-soluble material between 3 and 7 hr after infection. Most of the acid-soluble product is reincorporated into viral DNA. Incorporation of exogenous (3)H-adenine into viral DNA can be detected very early after infection (within the first 2 hr), but the bulk of viral DNA synthesis occurs between 6 and 8 hr. Both the breakdown of host DNA and the synthesis of viral DNA require protein synthesis during the first few hours of infection.