The discovery that viruses may be the most abundant organisms in natural waters, surpassing the number of bacteria by an order of magnitude, has inspired a resurgence of interest in viruses in the aquatic environment. Surprisingly little was known of the interaction of viruses and their hosts in nature. In the decade since the reports of extraordinarily large virus populations were published, enumeration of viruses in aquatic environments has demonstrated that the virioplankton are dynamic components of the plankton, changing dramatically in number with geographical location and season. The evidence to date suggests that virioplankton communities are composed principally of bacteriophages and, to a lesser extent, eukaryotic algal viruses. The influence of viral infection and lysis on bacterial and phytoplankton host communities was measurable after new methods were developed and prior knowledge of bacteriophage biology was incorporated into concepts of parasite and host community interactions. The new methods have yielded data showing that viral infection can have a significant impact on bacteria and unicellular algae populations and supporting the hypothesis that viruses play a significant role in microbial food webs. Besides predation limiting bacteria and phytoplankton populations, the specific nature of virus-host interaction raises the intriguing possibility that viral infection influences the structure and diversity of aquatic microbial communities. Novel applications of molecular genetic techniques have provided good evidence that viral infection can significantly influence the composition and diversity of aquatic microbial communities.

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Virioplankton: viruses in aquatic ecosystems

Cyanobacteria are oxygenic photosynthetic bacteria that have been used increasingly to study diverse biological processes, including photosynthesis and its regulation; cell differentiation and N2 fixation; metabolism of nitrogen, carbon, and hydrogen; resistance to environmental stresses; and molecular evolution. Many vectors and other genetic tools have been developed for unicellular and filamentous strains of cyanobacteria. Transformation, electroporation, and conjugation are used for gene transfer. Diverse methods of mutagenesis allow the isolation of many sought-for kinds of mutants, including site-directed mutants of specific genes. Reporter genes permit measurement of the level of transcription of particular genes, and assays of transcription within individual colonies or within individual cells in a filament. Complete genomic sequences have been obtained for the unicellular cyanobacterium, Synechocystis sp. strain PCC 6803 and the filamentous, heterocyst-forming cyanobacterium, Anabaena sp. strain PCC 7120. Genomic sequence projects are under way for Nostoc punctiforme strain PCC 73102 (ATCC 29133) and strains of the unicellular genera, Synechococcus, Prochlorococcus, and Gloeobacter. Genomic sequence data provide the opportunity for global monitoring of changes in genetic expression at transcriptional and translational levels in response to variations in environmental conditions. The availability of genomic sequences accelerates the identification, study, modification and comparison of cyanobacterial genes, and facilitates analysis of evolutionary relationships, including the relationship of chloroplasts to ancient cyanobacteria. The many available genetic tools enhance the opportunities for possible biotechnological applications of cyanobacteria.

Genetic tools for cyanobacteria.

Theory and applications of free-electron vortex states

Viruses may be major structuring elements of phytoplankton communities and hence important regulators of nutrient and energy fluxes in aquatic environments. In order to ascertain whether viruses are potentially important in dictating phytoplankton community structure, it is essential to determine the extent to which representative phytoplankton taxa are susceptible to viral infection. We used a spiral ultrafiltration cartridge (30,000-molecular-weight cutoff) to concentrate viruses from seawater at efficiencies approaching 100%. Natural virus communities were concentrated from stations in the Gulf of Mexico, a barrier island pass, and a hypersaline lagoon (Laguna Madre) and added to cultures of potential phytoplankton hosts. By following changes in in vivo fluorescence over time, it was possible to isolate several viruses that were pathogens to a variety of marine phytoplankton, including a prasinophyte (Micromonas pusilla), a pennate diatom (likely a Navicula sp.), a centric diatom (of unknown taxa), and a chroococcoid cyanobacterium (a Synechococcus sp.). As well, we observed changes in fluorescence in cultures of a cryptophyte (a Rhodomonas sp.) and a chlorophyte (Nannochloropsis oculata) which were consistent with the presence of viral pathogens. Although pathogens were isolated from all stations, all the pathogens were not isolated from every station. Filterability studies on the viruses infecting M. pusilla and the Navicula sp. showed that the viruses were consistently infective after filtration through polycarbonate and glass-fiber filters but were affected by most other filter types. Establishment of phytoplankton-pathogen systems will be important in elucidating the effect that viruses have on primary producers in aquatic systems.

https://aem.asm.org/content/aem/57/3/721.full.pdf

Use of Ultrafiltration To Isolate Viruses from Seawater Which Are Pathogens of Marine Phytoplankton

Physiology and cytological chemistry blue-green algae.

USING the methods of Safferman and Morris1, who isolated the first phycovirus, strain LPP-1, and propagated it on the blue green alga, Plectonema boryanum, five strains of cyanophages2 have been isolated from local polluted pond waters. Two of these differ in host range and plaque morphology wrhile the remaining three bring about lysis of LPP-1 host, P. boryanum, although showing variation in growth behaviour and plaque size. The first two strains infect either spore forming and/or heterocystous blue green algae and are inactive on. P. boryanum. One of these which has been isolated on a species of Cylindrospermum, forming heterocysts at both ends of its filaments and subterminal chains of spores, has a restricted host range. It does not infect other strains of Cylindrospermum with a similar morphology or Andbaena doliolum, another heterocystous and spore forming blue green alga. The second isolate causes lysis of three spore forming blue green algae, Anabaenopsis raciborskii, A. circularis and Raphidiopsis indica., of which the first two are also heterocystous. Tho first isolate is designated C-1 and the second AR-1 following the terminology of Safferman and Morris1 for LPP-1, which is based on the first letter of the genus name of the host algao. Strain C-1 causes fast lysis of the host in liquid medium and on agar plates. Plaques appear late but their size increases very fast and the entire algal growth on the plate is lysed within a few days. AR-1 plaques are irregular in comparison with LPP-1. Their size increases with longer incubation. After 16 days plaque size varies from 5 mm to 14 mm (Fig. 1). The margin of the plaque is frayed because of the filamentous nature of the host algae. The notable characteristic of strains C-1 and AR-1 is that they do not lyse spores and heterocysts which remain unaffected in plaques or lysates (Figs. 3 and 4). The gas vacuoles of the algae possessing them also remain unaffected by the strain AR-1, leaving trails of gas vacuoles behind (Figs. 2, 3.and 4).

Isolation of Cyanophages from India

SEVERAL authors1–3 have induced mutations in blue–green algae by ultraviolet irradiation, but the mutation reported here seems particularly significant because it obscures the criteria for delimitation of taxa in the Cyanophyceae4. True branching is a distinctive feature of the algae comprising the order Stigonematales4 and is absent in Nostocales, although algae of the family Scytonemataceae of the latter order show false branching. This is the first report of a mutation induced by ultraviolet irradiation leading to true branching in the typically unbranched genus Nostoc of the order Nostocales.

Induction by ultraviolet irradiation of mutation in the blue-green alga Nostoc linckia (Roth) Born. et Flah.

THE blue-green alga, Cylindrospermum majus Kuetz., forms a characteristic filament with single terminal heterocyst and sub-terminal spore at both ends of the filament. The alga was isolated on Alien and Arnon's nitrogen-free medium1 in axenic cultures. At one stage of the growth cycle most of the filaments of the alga form characteristic spores, which are ellipsoidal with sculptured dark-brown exospore wall.

Genetic Recombination in a Blue-green Alga, Cylindrospermum majus Kuetz.

THE study of low-latitude whistlers dates back to the pioneering work of Japanese scientists. The whistlers were first recorded at Toyokawa (geomag. lat., 24.5°N)1, and later efforts were made to record them at lower latitudes. The first successful records of whistlers in India were obtained at Gulmarg (geomag. lat., 24°10′N) by Somayajulu et al.2. Recording was later carried out at Nainital (geomag. lat., 19°1′N) and whistlers with comparatively lower dispersion and reduced rate of occurrence were reported3–5. Unsuccessful efforts were also made to record whistlers at Varanasi (geomag. lat., 15°6′N). Analysis of the low latitude whistler records by Rao et al.6 showed that the low-latitude whistler cut-off lies around 15° latitude, and apparently provided the reason for the non-recording of whistlers at Varanasi. Using an improved system, we have succeeded in recording whistler activity at Varanasi, and we describe here the categories of sonograms recorded in April, 1976.

Whistlers recorded at Varanasi

ELECTROMAGNETIC waves of very low frequencies (VLF) are generated by a variety of natural processes. This letter is to offer support for the Cerenkov process, in which radiation is produced by the interaction of moving electrons with the ambient plasma.

R. N. Singh

Papers

Isolation of Cyanophages from India

Induction by ultraviolet irradiation of mutation in the blue-green alga Nostoc linckia (Roth) Born. et Flah.

Genetic Recombination in a Blue-green Alga, Cylindrospermum majus Kuetz.

Whistlers recorded at Varanasi

VLF Wave Generation by the Čerenkov Process in the Inner Magnetosphere