Figure 1

Screening and electron microscopy of bacteriophage 0305φ8-36. Bacteriophage 0305φ8-36 was initially propagated and isolated [17] from soil frequented by cattle at the King Ranch (Kingsville, Texas). The host was a locally isolated Bacillus that was typed as B. thuringiensis by sequencing of the gene for 16s ribosomal DNA, as previously described [17]. During isolation, single-plaque cloning was performed [17] in gels of 0.40%, 0.20% and 0.15% agarose. The inocula for all three Petri plates were bacteriophages from a single plaque of the previous propagation, transferred by sterile needle and then non-uniformly spread [17]. The three Petri plates were at the same temperature (±0.2 C) during incubation. Photographic images are shown of Petri plates used for propagation in agarose gels of the following percentages: (a) 0.4, (b) 0.20, (c) 0.15. (d) In a more comprehensive experiment, plots of plaque diameter as a function of agarose gel percentage were made for bacteriophages G, T4 and 0305φ8-36 (0305φ8-36 is abbreviated by 36 in the figure). The molten agarose solution was the same among the different bacteriophages in (d). The host for bacteriophage G was Bacillus megaterium; the host for T4 was Escherichia coli BB/1. All Petri plates for (d) were in contact with the same surface and the temperature did not vary among them by more than 0.2°C. (e) Electron microscopy was performed of bacteriophage 0305φ8-36 negatively stained with sodium phosphotungstate after purification from a plate stock by use of a cesium chloride step gradient [17]. The length of the bar is 0.1 μm; magnification calibration was checked with a diffraction grating. The tails of all bacteriophage particles have partially contracted. By this criterion, 0305φ8-36 is a myovirus.