MONOPHASIC NATURE OF SAL. ABORTUS-—EQUI.

Sal. abortus-equi hs been known as a monophasic type which is stable
in both phase-1 (a) and phase-2 (e,n,x). An alternative phase is obtained by the
antiserum selection for rare variations. The presence of a suppressed Hj] locus
in piase-2 cell is demonstrated by transduction of Ny* allele, as well as
HO", to the other recipient (Lederberg and Edwards, 1953). Therefore, the
strain has the genotype Hy"H5°"", but Ho°™* is stabilized in both active-
and inactive-states. An analysis of a factor which stabilizes Ho state will be

reported here,

A strain of Sal. abortus-equi, SW726, was used for the experiment. The
strain is very slow motile in both phases. The motility is slower in phase-1
than in phase-2. Selection of a fast motile variant by NGA deep tube cultures

has been unsuccessful.

For the transvuctional experiment, e,n,x~phase of SW726 was used as a
donor and i-phase (phase-1) of diphasic Sal. typhimurium TM2 as a recipient.
Tfransductional types were screened by NGA plates supplemented anti~i serum and
anti e,n,x-serum at a dilution of 1/1000. Among 65 transductions obtained,

4 expressed diphasic a:1,2, 42 diphasic i:e,n,x and remaining 19 monophasic
e,n,x. That the hideen phase of the last type is i was demonstrated on three
PLT2: sensitive clones by transduction to Sal. paretyphi B SW666 b:-. These
results show that both @ and enx is transduced from the phase-2 culture, and
when a is transduced the resulted transductiona.remain as diphasic strains
whereas when e,n,x is transduced some transducthonal clones become to be
monopi:asic. By anti-enx NGA selection, i-phase cultures ere obtained rarely
from the e,n,x-monophasic transductional clones. ‘The i-phase cultures thus
obtained are also monophasic.

The stabilization of Ho state in Sal. abortus-equi is therefore caused
by a gene which is linked to Hp. The controller of Ho stability will be
given a syubol Shp. The genotype of SW726 is described as Hy°Ho®"* Sho-.