SUMMARYThree physiological types of coliphage were recognized on the basis of the effect of temperature on their e.o.p. High temperature (HT) phages plated at or above 25 °C, low temperature (LT) phages at or below 3o °C and mid-temperature (MT) phages in the range 15 to 42 °C. Only LT phages were found for Aeromonas hydrophila, an indigenous water organism. The maximum and minimum plating temperatures were stable properties of the virus and were not influenced by the growth temperature of the host. Temperature was found to affect the adsorption of two phages and to affect multiplication, but not adsorption, of another two. The distribution of the three types of phage correlated closely with the temperature of the environment from which they were isolated. The ecological implication of these results is discussed.

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A distinctive strain of tobacco necrosis virus (TNV) of unknown source was repeatedly isolated from water of the River Avon (Warwickshire) and two of its tributaries (R. Swift and R. Alne) using a technique developed for the concentration and isolation of water-borne bacteriophages. The same strain was isolated from the rivers Cam and Thames and from Lake Esthwaite (Cumbria) together with tomato bushy stunt virus.The TNV strain, designated Chenopodium necrosis (TNV-CN) was mechanically transmissible to C. amaranticolor and C. quinoa in both of which it caused local lesions and systemic infection. TNV-CN caused no infection when inoculated to tobacco (Nicotiana tabacum cv. White Burley) plants.The virus was not adsorbed to soil, could be isolated from leachate of soil in which systemically infected C. quinoa were grown and C. quinoa plants became infected when grown in soil watered with suspensions of the virus.The virus was not transmitted by Myzus persicae but was vectored by the zoospores of a lettuce isolate of Olpidium brassicae.TNV-CN was infective after 10 min at 85 "C, 3 wk at 20 OC and when diluted to lov8 but not Purified virus preparations contained c. 26 nm isometric virus particles.TNV-CN contained single-stranded RNA (mol. wt 1.5 x lo6) and one protein (mol. wt c. 26-4 x lo3) which co-electrophoresed in polyacrylamide gels with the protein of the D strain of TNV (TNV-D). Analytical centrifugation of TNV-CN indicated a single component virus with the same sedimentation coefficient = 115s) and buoyant density (1.385) in a CsCl gradient as those of TNV-D.TNV-CN and TNV-D were indistinguishable serologically.

The methods used for concentrating animal viruses from drinking water were found to be unsuitable for the concentration of bacteriophages from natural waters. The factors affecting recovery were investigated and a concentration procedure devised which is amenable to larger scale and field use. This procedure involves: (1) passage of the water through a sand filter; (2) removal of dissolved organic material with an anion exchange resin; (3) addition of MgCl2 to a final concentration of 5 times 10‐4m; (4) adjustment of the pH value to 3°8; (5) adsorption of the bacteriophages on to fibre glass and cellulose nitrate filters; (6) elution of bound phage with 3% (w/v) beef extract, and (7) concentration by ultrafiltration of the resulting eluates. Using this procedure a wide range of test bacteriophages was concentrated from 41 to 5 ml with recoveries ranging from 18–80%—concentration factors of 200–900 fold.