Imagine the open ocean as a microbial megacity（大城市）, teeming with（富于，充满） life too small to be seen. In every drop of water, hundreds of types of bacteria can be found. Now scientists have discovered that communities of these ocean microbes have their own daily cycles -- not unlike the residents of a bustling city who tend to wake up, commute, work, and eat at the same times. What's more, it's not all about the sun. Light-loving photoautotrophs（光合自养生物） -- bacteria that need solar energy to help them photosynthesize food from inorganic substances -- have been known to sun themselves on a regular schedule. But in a new study published in the July 11 issue of the journal Science, researchers working at Station ALOHA, a deep ocean study site 100 km north of Oahu, observed different species of free-living, heterotrophic bacteria turning on diel（一昼夜的） cycling genes at slightly different times -- suggesting a wave of transcriptional activity that passes through the microbial community each day.

"I like to say they are singing in harmony," said Edward F. DeLong, professor of Oceanography at University of Hawaii at Manoa and the head of the Massachusetts Institute of Technology team that made this discovery.

"For any given species, the gene transcripts for specific metabolic pathways turn on at the same time each day, which suggests a sort of temporal compartmentalization," said DeLong, who was the first scientist to be hired by the University under the auspices of（由……赞助） the Hawai'i Innovation Initiative. "It's a biologically and biogeochemically relevant new result."

The observations were made possible by advanced microbial community RNA sequencing techniques, which allow for whole-genome profiling of multiple species at once. The work was a collaboration between the Monterey Bay Aquarium Research Institute and DeLong's team, who together employed a free-drifting robotic Environmental Sample Processor (ESP) as part of a Center for Microbial Oceanography: Research and Education (C-MORE) research cruise at Station ALOHA. Riding the same ocean currents as the microbes it follows, the ESP is uniquely equipped to harvest the samples needed for this high-frequency, time-resolved analysis of microbial community dynamics.

What scientists saw was intriguing: different species of bacteria expressing different types of genes in different, but consistent, cycles -- turning on, for example, the type of restorative genes needed to rebuild their solar-collecting powers at night, then ramping up with different gene activity to build new proteins during the day. "The regularity and timing of individual microbial activities is somewhat like a new shift of hourly workers punching in and out of the clock, day after day," DeLong said.

The coordinated timing of gene firing across different species of ocean microbes could have important implications for energy transformation in the sea. Marine microbes are critically linked to ocean health and productivity. The mechanisms that regulate this periodicity（周期性，频率） remain to be determined.