Abstract
Current cyanobacterial model organisms were not selected for their growth traits or potential for the production of renewable biomass, biofuels, or other products. The cyanobacterium strain BL0902 emerged from a search for strains with superior growth traits. Morphology and 16S rRNA sequence placed strain BL0902 in the genus Leptolyngbya. Leptolyngbya sp. strain BL0902 (hereafter Leptolyngbya BL0902) showed robust growth at temperatures from 22°C to 40°C and tolerated up to 0.5 M NaCl, 32 mM urea, high pH, and high solar irradiance. Its growth rate under outdoor conditions rivaled Arthrospira (“pirulina” strains. Leptolyngbya BL0902 accumulated higher lipid content and a higher proportion of monounsaturated fatty acids than Arthrospira strains. In addition to these desirable qualities, Leptolyngbya BL0902 is amenable to genetic engineering that is reliable, efficient, and stable. We demonstrated conjugal transfer from Escherichia coli of a plasmid based on RSF1010 and expression of spectinomycin/streptomycin resistance and yemGFP reporter transgenes. Conjugation efficiency was investigated in biparental and triparental matings with and without a “elper”plasmid that carries DNA methyltransferase genes, and with two different conjugal plasmids. We also showed that Leptolyngbya BL0902 is amenable to transposon mutagenesis with a Tn5 derivative. To facilitate genetic manipulation of Leptolyngbya BL0902, a conjugal plasmid vector was engineered to carry a trc promoter upstream of a Gateway recombination cassette. These growth properties and genetic tools position Leptolyngbya BL0902 as a model cyanobacterial production strain.
Highlights
Great interest is being focused on photosynthetic microorganisms for their ability to convert solar energy and CO2 into fuels and other bioproducts
We have identified and characterized the cyanobacterial strain Leptolyngbya sp. strain BL0902, which emerged from a screen of cyanobacterial strains for superior growth traits, and show that it is amenable to genetic manipulation
Morphological description and identification Leptolyngbya BL0902 is a filamentous cyanobacterium without heterocysts, akinetes, or true or false branching; filaments are composed of single trichomes that are straight to wavy and lack conspicuous motility
Summary
Great interest is being focused on photosynthetic microorganisms for their ability to convert solar energy and CO2 into fuels and other bioproducts. Cyanobacteria typically accumulate glycogen and polyhydroxyalkanoates rather than lipids as stored energy, but their photosynthetic membranes are rich with glycolipids and they naturally produce hydrocarbons [4,6], the major constituents of gasoline, diesel, and jet fuel [7]. Cyanobacteria usually have higher growth rates than other phytoplankton under low light [14] In addition to their physiological and ecological variety, cyanobacteria are diverse in terms of morphology, including multicellular filamentous species that may bioflocculate or float to the surface of a pond for easier harvesting. These characteristics reflect their genetic diversity and make them good sources for gene mining
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