As the temperatures rise and Americans swarm to the beach, they slather on sunscreen to protect against the sun’s harmful UV radiation that causes skin cancer. As they splash and swim, few give thought to whether the chemicals in the lotions and sprays are safe for marine organisms such as the fish and corals living in these coastal zones.
The bad news is that mounting evidence suggests that certain chemicals in these radiation filters are bleaching the corals and killing fish. The good news is that there is a greener, cleaner, and safer alternative in the works.
The sunscreens widely available belong to two major categories: physical and chemical. Physical sunscreens contain tiny minerals that act as a shield deflecting the sun’s rays. On the other hand, chemical sunscreens use many synthetic compounds that absorb UV light before it reaches the skin.
But these lotions wash off in water. For example, for every 10,000 visitors frolicking in the waves, about 4 kilograms of mineral particles are washed into the beach water each day. These minerals catalyze the production of hydrogen peroxide, a well-known bleaching agent, at a concentration high enough to harm coastal marine organisms. Up to 14,000 tons of sunscreens are released into the water each year. Active ingredients in these sunscreens, minerals and synthetic organic compounds, are putting 10 percent of the global reefs under stress, including 40 percent of coral reefs along the coast.
To ramp up shinorine production, we sought a fast-growing strain of cyanobacteria that would thrive under predictable conditions. This took a lot of work! We decoded the genetic blueprints—genomes—of more than 100 varieties of cyanobacteria from marine and terrestrial ecosystems and selected one, Fischerella sp. PCC9339, to cultivate in the laboratory.
To our delight, after four weeks this strain produced shinorine, but unfortunately not enough. To produce more we then transferred a set of genes that encode the instructions to make shinorine, into one freshwater cyanobacterium (from Berkeley, California), Synechocystis sp. PCC 6803, which grows fast with just water, carbon dioxide and sunlight. Using the engineered cyanobacterium, we produced a quantity of shinorine comparable to the conventional method—but we did it in just a few weeks instead of one year that’s needed to cultivate red algae.
By advancing the method to produce more shinorine and other UV-absorbing natural products, we hope to make “green” sunscreens more available—to protect our skin and the lives of the creatures we are so eager to see.