A Defective Generalized Transducing Bacteriophage in Xanthobacter autotrophicus GZ29

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Abstract
A small defective generalized transducing bacteriophage (CA3) was detected in culture supernatants of the nitrogen-fixing hydrogen bacterium X. autotrophicus GZ29. This phage had a head diameter of 37-43 nm and it had a low specific density of 1.349 g cm-3, probably due to a small DNA molecule of 3.3 .times. 106 MW. The phage did not form plaques on any of the X. autotrophicus strains tested and therefore was detectable only by its transducing activity and by EM. All genetic markers tested were transducible at frequencies of about 10-4/marker per phage particle. No cotransduction of markers was detected. Due to the high transduction rate and the small size of the DNA molecule, it is assumed that CA3 particles contain mainly or exclusively chromosomal DNA.