Preferential selection of VP7 gene from a parent rotavirus strain (SA11) in sequential passages after mixed infection with SA11 and SA11-human rotavirus single-VP7 gene-substitution reassortants.

We studied the competitive growth among SA11-L2(G3) and its single-human VP7 gene-substitution reassortants SA11-L2/KU-R1(G1) and SA11-L2/DS1-R1(G2), which have the genetic background of SA11-L2, during sequential passages after mixed infection. When the same infectious units (m.o.i. of 5 p.f.u./cell) of SA11-L2 and a reassortant SA11-L2/KU-R1 were inoculated onto and passaged in MA104 cells, 88% of the virus clones isolated from the culture fluid at the 3rd passage belonged to G3, and all the clones from the 10th passage had G3 specificity. Even when SA11-L2/KU-R1 with titer 10 times higher than that of SA11-L2 was used in the coinfection, the predominance of clones with G3-VP7 was observed. Although G2 clones slightly surpassed G1 clones in number in the mixed culture of SA11-L2/KU-R1 and SA11-L2/DS1-R1, G3 clones predominated in the virus progeny from a mixed culture infected with the same titers of SA11-L2, SA11-L2/KU-R1, and SA11-L2/DS1-R1. However, no significant difference in viral growth was detected among SA11-L2 and the two reassortants.