Loss of genes for DNA recombination and repair in the reductive genome evolution of thioautotrophic symbionts of Calyptogena clams

Table 4 Effect of mutY on the GC content of ribosomal RNA genes in Calyptogena clam symbionts

Host clam	Clade	mutY	16S rDNA		23S rDNA
			Length (bp)	G+C%	Length (bp)	G+C%
Calyptogena kilmeri	I	-	1428	48.79	2519	48.14
C. kawamurai	I	-	1510	48.77	2519	47.94
C. soyoae	I	-	1508	48.77	2525	48.13
C. laubieri	I	-	1343	48.65	2519	48.25
C. okutanii	I	-	1468	48.87	2525	48.12
C. magnifica	II	-	1468	50.20	2536	48.94
Mean	I + Rma*			49.01#		48.25§
SD				0.59		0.35
Mean	I only			48.77$		48.12!
SD				0.08		0.11
C. phaseoliformis	II	+	1506	50.41	2530	49.81
C. fossajaponica	II	+	1467	50.64	2531	49.99
C. stearnsii	II	+	1467	49.90	2535	49.07
C. nautilei	II	+	1506	49.90	2528	49.36
C. fausta	II	+	1507	50.13	2534	49.31
C. pacifica	II	+	1428	50.27	2532	49.25
Mean	II except Rma*			50.21#$		49.47§!
SD				0.29		0.36

*Ca. Ruthia magnifica (symbiont of C. magnifica)
#Difference between G+C contents of 16S rRNA genes of clade I symbionts+Rma and of clade II symbionts except Rma was significant (p = 0.00119) in the t-test.
$Difference between G+C contents of 16S rRNA genes of clade I symbionts and of clade II symbionts except Rma (p = 0.00257) was significant in Welch's test.
§Differences between G+C contents of 23S rRNA genes of clade I symbionts+Rma and of clade II symbionts (p = 0.00014) was significant in the t-test.
!Difference between G+C contents of 23S rRNA genes of clade I symbionts and of clade II symbionts (p = 2.014e-5) was significant in the t-test.