title: The freshwater cyanobacterium Anabaena doliolum transformed with ApGSMT-DMT exhibited enhanced salt tolerance and protection to nitrogenase activity, but became halophilic.
abstract: Glycine betaine (GB) is an important osmolyte synthesized in response to different abiotic stresses, including salinity. The two known pathways of GB synthesis involve: 1) two step oxidation of choline (choline → betaine aldehyde → GB), generally found in plants, microbes and animals; and 2) three step methylation of glycine (glycine → sarcosine → dimethylglycine → GB), mainly found in halophilic archaea, sulphur bacteria and the cyanobacterium Aphanothece (Ap.) halophytica. Here, we transformed a salt-sensitive freshwater diazotrophic filamentous cyanobacterium Anabaena (An.) doliolum with N-methyltransferase genes (ApGSMT-DMT) from Ap. halophytica using the triparental conjugation method. The transformed An. doliolum synthesized and accumulated GB in cells, and showed increased salt tolerance and protection to nitrogenase activity. The salt responsiveness of the transformant was also apparent as GB synthesis increased with increasing concentrations of NaCl in the nutrient solution, and maximal [12.92 µmol (g dry weight)(-1)] in cells growing at 0.5 M NaCl. Therefore, the transformed cyanobacterium has changed its behaviour from preferring freshwater to halophily. This study may have important biotechnological implications for the development of stress tolerant nitrogen-fixing cyanobacteria as biofertilizers for sustainable agriculture.
authors: Department of Botany, Banaras Hindu University, Varanasi 221 005, India.
authors: Meenakshi
authors: M
authors: Singh
authors: Department of Botany, Indira Gandhi National Tribal University, Amarkantak, (M.P.) 484886, India.
authors: Naveen K
authors: NK
authors: Sharma
authors: Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi 221 005, India.
authors: Shyam Babu
authors: SB
authors: Prasad
authors: Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi 221 005, India.
authors: Suresh Singh
authors: SS
authors: Yadav
authors: Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi 221 005, India.
authors: Gopeshwar
authors: G
authors: Narayan
authors: Department of Botany, Banaras Hindu University, Varanasi 221 005, India.
authors: Ashwani K
authors: AK
authors: Rai
mesh_terms: D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics / Q000502:physiology*; D005618:Fresh Water / Q000382:microbiology; D009591:Nitrogenase / Q000378:metabolism*; D011496:Protein Methyltransferases / Q000235:genetics / Q000378:metabolism*; D055049:Salt Tolerance; D012965:Sodium Chloride / Q000378:metabolism*; D014169:Transformation, Bacterial
chemical_list: D012965:Sodium Chloride; D009591:Nitrogenase; D011496:Protein Methyltransferases