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Title: Overexpression of HlyB and Mdh genes confers high salinity tolerance (halotolerance) in Fremyella diplosiphon, a Freshwater Cyanobacterium

Author
item TABATABAI, BEHNAM - Morgan State University
item ARUMANAYAGAM, ANITHACHRISTY - Houston Methodist Research Institute
item ENITAN, OLUWATOMISIN - Morgan State University
item MANI, ARUNMANI - University Of Texas Health Science Center
item Natarajan, Savithiry - Savi
item SITTHER, VIJI - Morgan State University

Submitted to: Enzyme and Microbial Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2017
Publication Date: 8/2/2017
Citation: Tabatabai, B., Arumanayagam, A.S., Enitan, O., Mani, A., Natarajan, S.S., Sitther, V. 2017. Overexpression of HlyB and Mdh genes confers high salinity tolerance (halotolerance) in Fremyella diplosiphon, a Freshwater Cyanobacterium. Enzyme and Microbial Technology. 103:12-17. https://doi.org/10.1016/jenzyme.2017.04009.
DOI: https://doi.org/10.1016/jenzyme.2017.04009

Interpretive Summary: Freshwater photosynthetic organisms including algae and cyanobacteria, which are potential sources for development of biofuels, are threatened by increasing salinity due to various environmental and human-related factors. Elevated salinity in these organisms leads to ion imbalance and hyperosmotic stress. Enhancing salinity tolerance (halotolerance) in these organisms is important. We identified halotolerance-linked genes and over-expressed the genes to confer halotolerance in the cyanobacterial species Fremyella diplosiphon. Development of halotolerant strains paves the way for their growth in marine waters. These results are important to scientists at universities, government agencies and private industry interested in developing these organisms for biofuel production.

Technical Abstract: Fremyella diplosiphon is a freshwater cyanobacterial species that has great potential for development as a commercial biofuel agent with the ability to grow in low light intensity and acclimation to different wavelengths of light. In the present study, expression plasmids harboring the hemolysin B (HlyB) and malate dehydrogenase (Mdh) genes were overexpressed in the wild type F. diplosiphon (Fd33) to enable its growth in 35 g/L sodium chloride (NaCl). Overexpression of the HlyB and Mdh genes resulted in a nine-fold and 20-fold, respectively, increase in gene expression. Enhanced mRNA expression was corroborated by up-regulation of protein expression at the expected size for HlyB and Mdh. In 2D-PGAGE the protein spot corresponding to HlyB in HSF33-1 gave a significant hit with a MOWSE score of 476 with 23% sequence coverage, and the protein spot corresponding to Mdh in HSF33-2 gave a significant hit with a MOWSE score of 404 with 22% sequence coverage. Physiological evaluation of the transformants in BG11/HEPES medium containing 35 g L-1 NaCl (seawater blend adjusted to 35 g L-1 NaCl) indicated the ability of transformants to grow in high salinity. No loss of phycobiliprotein or chlorophyll a accumulation was observed in the transformants grown in the seawater blend. The study indicates that up-regulation of HlyB and Mdh genes confer halotolerance to F. diplosiphon; thus enabling its growth in elevated NaCl equivalent to marine waters. This is the first report of HlyB and Mdh overexpression conferring halotolerance in F. diplosiphon.