Your Query returns 61 Accession Numbers:

* OMIM link based on symbol match for human and mouse.
** HUGO symbol

Gene/Allele	Accession	NCBI Taxonid	Synonyms
nirB	AL939112	100226	SC7A8.25 SCO2486
nirB	AL939112	100226	SC7A8.26 SCO2487
nirB	NC_003888	100226	SC7A8.25
nirB	NC_003888	100226	SC7A8.26
nirB	D16303	1131
nirB	U18997	562
nirB	AP005043	227882
nirB	BX248334	233413
nirB	AL627281	90370	STY4322
nirB	BX294136	243090
nirB	AJ414141	214092	YPO0161
nirB	AL646083	305	RS03166 RSp1222
nirB	AE000412	83333	b3365
nirB	AF308467	28451
nirB	AE005559	155864	Z4726
nirB	X56813	316
nirB	AL583926	1769	ML2555
nirB	AE009321	180835	Atu3902
nirB	BX842572	83332
nirB	AE013998	187410	y3945
nirB	AE015346	198214
nirB	AE016780	160488
nirB	AE016767	199310
nirB	AE004603	208964	nasD
nirB	AE000678	224324	aq_206
nirB	AE016847	209261
nirB	AE016992	198215
nirB	AE008859	99287	STM3474
nirB	AE017030	198094
nirB	AF029224	1281
nirB	AE016867	223283
nirB	AY492000	571
nirB	AE017240	262316
nirB	AE005174	83334	Z4726
nirB	AE000657	224324	aq_206
nirB	NC_000913	83333	nirD
nirB	NC_000918	224324
nirB	NC_002516	208964
nirB	NC_002655	155864
nirB	NC_004088	187410
nirB	NC_002947	160488
nirB	NC_004337	198214
nirB	NC_004431	199310
nirB	NC_004631	209261
nirB	NC_004578	223283
nirB	NC_003997	198094
nirB	NC_004741	198215
nirB	NC_002677	1769
nirB	NC_000962	83332
nirB	NC_003198	90370
nirB	NC_003143	214092
nirB	NC_002945	233413
nirB	NC_005027	243090
nirB	AE017127	229193
nirB	NC_002944	262316
nirB	NC_003197	99287
nirB	0	N/A
nirB	NC_003078	266834
nirB	NC_003155	227882
nirB	NC_003296	267608	RS03166
nirB	NC_003305	176299

Text2Knowledge ... Yong Huang 2002