TABLE 2.

Presumed nucleotide substitutions in sequences of cloned nitAB 16S rDNA fragments amplified from Arctic and Antarctic samples, relative to the sequence obtained directly from nitAB amplicons^a

Positionb	Direct sequence	Arctic clone												Antarctic clone
		95A-44	95B-3	95B-4	95B-7	95B-10	95B-22	96A-4	96A-8	96A-11	96A-17	96A-19	96B-3	Pal 6-2	Pal 6-8	Pal 6-13
182	T									C
208	C			T		T
249	T			A									A
264	A			G
272	A														T
280	G							T		T	A
299	A													G
327	C							T		T	T
388	A													T
412	G												T
456	T			A
470	C							T		T	T
475	T		C									C
481	A									G
486	A									G
500	C						T
511	T				C
521	C	T
578	C							G		G	G
586	T							G		G	G
609	G						T	T		T	T
636	C							T		T	T
729	G														A
761	G							C		C	C
837	G											A
947	T														C
1036	A		T
1093	A								G
1157	G														A
1170	A								G
1175	G															A
1178	G													A

^aTransversions are indicated in boldface. The area with italicized nucleotides corresponds to the portion of the sequence probed with DGGE primers.

^bNucleotide positions correspond to E. coli 16S rRNA positions (accession number J01695).