Specificity of amplification with 16S rDNA primers CYA359F and NITRO821R (a) or nifH primers CNF and CNR (20) (b). Lane Av, Anabaena variabilis; lane T, Trichodesmium sp. strain WH 9601; lane A, Anabaena sp. strain PCC7118; lane Pr, Planktothrix rubescens; lane S, Synechocystis sp. strain PCC6803; lane U, Synechococcus sp. strain CC9605; lane Y, Cyanothece sp. strain WH 8902; lane C, Cyanothece sp. strain WH 8904; lane PHLI, Prochlorococcus sp. strain EQPAC1; lane PHLII, Prochlorococcus sp. strain TAK9803-2; lane PLL, Prochlorococcus sp. strain MIT9313; lane N, Nostoc sp. strain PCC7120; lane M, Microcystis sp. strain PCC7806; lane G, Gloeotrichia sp.; lane Co, control (no DNA).