A search goes faster with a tool to separate the wheat from the chaff. A pan can help you find gold flakes, and a metal detector can help you find a coin at the beach, but what tools can you use when you’re searching for a bacterium that can manufacture biofuels? In a study in mBio this week, researchers applied an old familiar microscopy tool in a new high-throughput method to help identify new strains of hydrocarbon-making microbes.
The dye Nile red has been used in microscopy for years as a lipophilic stain. It is non-fluorescent in water, but once it partitions into an, oily, hydrophobic environment it lights up, offering microscopists a way to identify lipid globules within living cells. Prior studies have applied the dye to screen microbes for the production of fatty acids and esters and for isoprenoid-derived hydrocarbon production in microalgae.
Pinzon et al. set out to test the dye in a high-throughput screen for the production of hydrocarbons or ketones by recombinant bacteria. Using wild-type and recombinant strains of Shewanella oneidensis and Escherichia coli that express the enzyme OleA, which is known to initiate hydrocarbon biosynthesis, they put the dye to the test in microtiter plates. The method correctly identified strains that produced elevated levels of ketones. Under the microscope (see inset), these strains are surrounded by a red halo, indicating that the dye detected ketones localized in the membrane.