It was routinely used for spores of S. coelicolor A3(2), S. lividans
(Flett et al. 1997), S. clavuligerus (Fouces et al.
2000), S. nodosus (Nikodinovic et al. 2003) and several
other Streptomyces species with non–heat sensitive spores
(Voeykova et al. 1998). We investigated the effect of heat
treatment on the viability of spores and conjugation effi-
ciency of S. rimosus R7 and M4018. pIJ8600 harbouring
the thiostrepton resistance gene (tsr) (Sun et al. 1999)
was employed for conjugation experiments instead of the
commonly used pSET152 (Bierman et al. 1992) because
S. rimosus is resistant to apramycin used as a selective
marker in pSET152. The highest conjugation efficiencies
for both strains were achieved when spores were treated
at 40C for 10 min (1Æ46 · 10)2 and 3Æ45 · 10)3 for
strains R7 and M4018, respectively; Table 1), and the effi-
ciencies rapidly decreased when spores were incubated
above 40C. Interestingly, conjugation efficiencies with
non–heat treated spores were relatively high (3Æ33 · 10)3
and 8Æ13 · 10)4
, for strains R7 and M4018, respectively;
Table 1). Note that the reduction in conjugation effi-
ciency above 40C is much greater than the loss of spore
viability and that at 50C and 55C is lower than when
no heat treatment was applied, indicating that exposure
to these higher temperatures reduces the ability of the
germinated spores to participate in conjugation.
Ne