TABLE 2.

Recombination of M. barkeri ileS12 with M. acetivorans^a

Plasmid	Transformation efficiencyb (CFU/μg of DNA)
	Pu	PA	Pu + PA
pPB12	2.4 × 105	2.5 × 105	2.3 × 105
pPB18	0	14c	0

^aRecombination between the ileS alleles of M. barkeri and M. acetivorans was examined by transformation of M. acetivorans with plasmids carrying the M. barkeri ileS12 allele that confers PA^r. Plasmid pPB12 is capable of autonomous replication and served as a positive control for transformation frequency. Plasmid pPB18 cannot replicate in Methanosarcina and therefore can only give antibiotic-resistant transformants if it recombines with the host chromosome. 

^bTransformation frequencies are averages of two trials with selection on HS-MA agar plus puromycin (Pu), pseudomonic acid (PA), or puromycin plus pseudomonic acid (Pu + PA). 

^cNone of the PA^r transformants obtained with pPB18 were resistant to puromycin.