The Gluconobacter phage GW6210, infects the ATCC strain 621 of G. oxydans. This phage possesses a polygonal head and contractile tail; therefore, it can be placed morphologically into Bradley's group A and tentatively placed in the virus family Myoviridae. This intensive electron microscopic study shows phage GW6210 to have a polygonal head, collar, tail sheath, baseplate, and tail pins. This phage is primarily unusual because of its large size. Using Tobacco Mosaic Virus as an internal standard, the head was found to be 170 nm in diameter and the tail was 136 nm long and 34 nm wide. The phage preparation seemed to consist of two plaque types: a small clear plaque having a 0.3 ± 0.1 mm diameter surrounded by a large turbid region that measured 3.5 ± 0.7 mm wide, and a small turbid plaque that varied greatly in size (1.4 ± 0.8 mm). However, subsequent data indicated that these types represented size variation of a single plaque type. In addition to the normal host of GW6210, G. oxydans subspecies suboxydans ATCC 621, the host range of this phage includes: G. suboxydans var. α, IFO 12528; A. melanogenus, ICPB 2096; G. rubiginosis, IFO 3244. Fifty strains of Gluconobacter and 52 strains of Acetobacter were unaffected by the phage as weel as 3 strains of Pseudomonas tested. / Master of Science