Large-scale genetic variation of the symbiosis-required megaplasmid pSymA revealed by comparative genomic analysis of Sinorhizobium meliloti natural strains

Table 3 Experimental analysis of 118 genes from microarray hybridisation

P-value classes	N° of ORFs		Total ORFs amplified by PCR*	N° of ORFs positive to PCR amplification	N° of ORFs analysed by Southern blotting	N° of ORFs with duplication after Southern hybridisation**	N° of sequenced ORFs	N° of ORFs with nucleotide variation in the 70-mer oligo sequence
p < 0.001	66	log2-ratio < 0	19	19	7	7	-	-
		log2-ratio > 0	47	8	-	-	8	8
p > 0.001	52	log2-ratio < 0	21	21	4	0	-	-
		log2-ratio > 0	31	31	-	-	7	0

* PCR amplification was carried out with primer anchored to the flanking regions of the gene.
** Determined as higher number of observed fragments after Southern-blot analysis of Rm1021 and of the wild strain.

ISSN: 1471-2164