Effect of inorganic N on the population, in vitro colonization and morphology of Acetobacter diazotrophicus (syn. Gluconacetobacter diazotrophicus)

We investigated whether Acetobacter diazotrophicus (syn. Gluconacetobacter diazotrophicus) could be recovered only from sugarcane plants either with low or no application of fertiliser N. We report here the enrichment and enumeration of A. diazotrophicus from high N-fertilised samples where high heterotrophic populations reduce the numbers of A. diazotrophicus ultimately diminshing its isolation frequency as reported earlier. The growth medium of micropropagated sugarcane seedlings of the varieties Co 8021, Co 86249, Co 86010, Co 86032, and Co 87025 was amended with potassium nitrate, ammonium nitrate, ammonium chloride and urea. The colonisation and AR activity of A. diazotrophicus were affected in the presence of high levels (25 mM) of ammonium chloride and ammonium nitrate but remained unaffected in low levels of N (i.e 1/10th of MS liquid medium) and with high levels of potassium nitrate (25 mM) and urea (500 ppm). A. diazotrophicus was detected in the inoculated plants both at low and high levels of N based on the amplification of a specific 16S rRNA gene fragment using PCR based method targeting a stretch of 445 bp with primers AC and DI. High levels of N in the growth medium induced morphological changes on A. diazotrophicus cells resulting in long pleomorphic cells. The percentage of pleomorphic cells was in the decending order from NH4NO3, NH4Cl, KNO3, and urea. These changes were more prominent in ammonium chloride and ammonium nitrate than potassium nitrate, urea and N free medium. The morphological changes and the increased heterotrophic populations may play a role on the survival ofA. diazotrophicus in high N-fertilised samples/environments.