Science Concentrates SYNTHETIC BIOLOGY
Synchronized bacteria attack tumors Engineered microbes grow and burst in cycles to release anticancer molecules
case, the engineered circuit instructs the bacteria to make a small molecule called N-acyl-homoserine lactone. Once the bacteria reach a certain threshold population, To fight cancer, some researchers would explosions would help avert harmful unthe molecules activate quorum-sensing like to enlist the help of another of medicontrolled growth of bacteria, Fussenegger pathways in the genetic circuit and trigger cine’s foes: bacteria. Bacteria have an affinsays. the cells to lyse, or break open, spilling their ity for tumors’ low-oxygen and immuneTo program Salmonella bacteria to exanticancer cargo.About 10% of the bacteria cell-free environments. Through some ecute these cycles, the researchers, led by survive the resulting wave of destruction genetic engineering, scientists hope to proJeff Hasty at the University of California, and go on to restart the cycle. gram the microbes to kill malignant cells. San Diego, designed a genetic circuit with The researchers tested three strains of Now a team of synthetic biologists has two basic functions. First, the circuit tells these bacterial suicide squads in mice with designed bacteria that grow and die in prothe microbes to produce an anticancer mol- metastasized liver cancer. Each strain syngrammed cycles, allowing for a controlled ecule as they grow. “Then we program them thesized one of three anticancer payloads: release of anticancer molecules and preto commit suicide to deliver the drug,” a molecule that lyses mammalian cells, a venting unchecked bacterial growth (NaHasty says. cytokine that initiates an immune response ture 2016, DOI: 10.1038/nature18930). That second step involves quorum against the tumor, or a protein that triggers “This is a fascinating paper that blows sensing, a process in which bacteria comcancer cells to kill themselves. me away,” says Martin Fussenegger, a municate via molecules to coordinate their After 12 days, tumors in mice receivbioengineer at the Swiss Federal Instiactions, such as forming biofilms. In this ing the engineered bacteria were about tute of Technology, one-quarter the size of Zurich, who was not those in mice treated involved in the work. with normal Salmonella. “It describes an unconHasty considers this ventional, completely study a proof of prinnovel, yet highly promciple and cautions that ising strategy to use before any bacteria synchronized bacteria therapy can be tested that invade and kill in people, researchcancer cells by rhythers must understand mic ‘explosions.’ ” how the immune If bacterial antiAs engineered bacteria grow, they produce anticancer molecules and green system will respond cancer therapies ever fluorescent protein (left). When they reach a population threshold (center), a to the engineered mimake it to the clinic, quorum-sensing molecule triggers the cells to lyse, or burst open, releasing their crobes.—MICHAEL such synchronized payload (right). TORRICE
ENERGY STORAGE
CREDIT: NAT U RE
Catalytic membrane improves lithium-air batteries If lithium-air batteries lived up to their theoretical potential, they could provide roughly 10 times as much energy per weight as lithium-ion batteries. That level of performance could speed adoption of electric vehicles. But the air-breathing power sources fare poorly in the real world: They suffer from sluggish kinetics and short lifetimes. To address those issues, researchers have modified the standard lithium-air battery design by including a catalytic membrane adjacent to the electrode at which oxygen from the air reacts (Nano Lett. 2016, DOI: 10.1021/acs.nanolett.6b00856). That design extends battery lifetime by
improving reversibility of the electrochemical reactions and it boosts the efficiency of the battery’s power generation. The new design also provides a way to analyze products formed during battery charging cycles to better understand the underlying electrochemistry. A key problem impeding lithium-air batteries is the formation of lithium oxides such as Li2O2 on the air-breathing electrode (cathode) during discharge. These solids accumulate on the cathode surface and bury catalytic sites needed to reverse oxide formation. Won-Hee Ryu and André D. Taylor of
Yale University and colleagues proposed that moving the catalyst away from the cathode surface may protect the catalyst and improve battery performance. So they decorated a porous aluminum oxide membrane with catalytic palladium particles and positioned the membrane near the cathode. When the team examined the membranes afterward, they found that lithium oxides had formed on the catalytic membrane but did not bury the catalyst particles. The particles remained accessible during charging to decompose the lithium oxides, reversing the electrochemical reaction.—MITCH JACOBY JULY 25, 2016 | CEN.ACS.ORG | C&EN
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