Detection of nifH Sequences in sugarcane (Saccharum officinarum L.) and pineapple (Ananas comosus [L.] Merr.)

To detect N-2-fixing bacteria in a plant without using culture methods, nifH gene segments were amplified with degenerate primers from DNA extracted from stems of sugarcane (Saccharum officinarum L.) and leaves of pineapple (Ananas comosus [L.] Merr.). Sequences of the nifH clones were homologous to those of bacteria in the genera Bradyrhizobium, Serratia, and Klebsiella. The bacteria with nifH sequences homologous to those of the three genera may be promising candidates for predominant endophytic diazotrophs in sugarcane and pineapple, because these sequences were commonly detected in samples from different host plants, which were collected at different locations. On the other hand, no nifH sequence related to Gluconacetobacter diazotrophicus, which is an endophytic N-2-fixing bacterium and had been previously isolated from sugarcane, was detected in sugarcane. This indicates the absence or the presence of few G. diazotrophicus in the stems of the sugarcane plants used in the current study.