ostensibly beneficial bugs with those whose mucus has been delib- Rosenberg suspects that the symbiosis that develops between
erately inoculated with such microbes. various microbes and corals might even have evolutionary sig-
Rosenberg’s group is about to do just that. It’s a necessary test nificance. For instance, in 1995, Kushmaro linked devastating
for the “probiotic hypothesis” that his bleaching incidents in the Mediter-team announced in the December 2006 ranean Sea’s Oculina patagonica coral
Environmental Microbiology. Rosen- to an infection by Vibrio shilonii. It
berg, Smith, and other members of the was the first time that coral bleaching
United Nations’ Coral Disease Working had been traced to a bacterial infec-Group further describe the idea in the tion, and bleaching infections recurred
March Oceanography. every summer through 2002.
Probiotics typically are bacteria-laden By the following summer, however,
dietary supplements for people (SN: the coral’s vulnerability had disap-
2/3/01, p. 68) or animals (SN: 3/28/98, peared. Sampling its mucus turned up
p. 196). By seeding the body with bacte- no V. shilonii, and deliberately inocu-ria that enhance immunity or other ben- lating the mucus with the bug “does not
eficial biological functions, probiotic result in coral bleaching,” Rosenberg’s
treatments seek to prevent disease or group reports in the May Nature
restore health. Lately, marine biologists Reviews Microbiology. Indeed, they
have begun embracing the idea that TEEMING HORDES — Magnified bacteria— find that within 4 days, the added
corals may exude compounds to lure stained yellow to highlight them—fill this mucus germs can no longer be found.
beneficial microbes into their mucus to from near a coral's surface. It appears, Rosenberg says, that the
create a probiotic community. corals recruited mucus microbes to
The idea makes intuitive sense, Bythell says. Many probiotics quash the would-be killer germs. Certainly, the corals didn’t have
target the gut, attempting to overwhelm pathogenic bacteria with enough time to evolve resistance on their own, he says. But by
a huge, replenishing dose of beneficial ones. Coral mucus resem- developing new symbiotic relationships with bacteria or phages,
bles mucus lining the human gut. In fact, he says that a medical col- they adapted to the germs’ presence.
league to whom he showed a photo of a coral’s mucus-producing Similarly, photosynthetic bacteria have been found in some coral
cells was stunned. “If you told me this was a human gut, I’d have tissues, suggesting a way in which the animals might gain suste-believed you,” Bythell recalls him saying. nance when high temperatures send their algal symbionts fleeing.
Gut flora—largely beneficial bacteria—helps digest foods, boost Taken together, the new findings give some reason for optimism
immunity, and prevent colonization by germs. Corals, one of the about the globe’s besieged corals. In view of rising concerns about
animal kingdom’s most primitive multicellular families, appear to global warming’s threat to corals, Rosenberg suggests, it could be
accomplish the same thing, he says, using “a mucosal system that’s that corals can adapt to environmental change more rapidly than
virtually identical, structurally, to our gut.” their own genes would permit. ■
WILD
(continued from page 345)
To demonstrate how these properties can work in concert, he
and his team grew a forest of upright zinc oxide nanowires, each
of them a perfect crystal. The
researchers then lowered an array
of sharp nanoscale electrodes fabricated by similar techniques, leaving just enough space so that when
the nanowires flex, they touch the
electrode tips.
When ambient vibration or other
mechanical energy deflects the
nanowires, they develop piezoelectric voltages that move charges
within the semiconducting material. During the periodic contacts
between the nanowires and the
electrodes, those charges move into
the electrodes.
This effect could be the basis of
energy scavengers with efficiencies
as high as 30 percent, Wang predicts. “I have a high hope that we
will be able to market commercial
zinc oxide nanogenerators within 3
years,” he says.
ONBOARD ENERGY MANAGEMENT Efficiency is also a
major goal of electrical engineers and software designers working
on a third piece of the energy-scavenging challenge—managing
how the energy is employed by the sensor package itself. One frequently used strategy is to have the devices spend most of their existence in sleep mode, where they can survive on just the barest trickle
of power. They have to wake up for only a tiny fraction of a second
every now and then to take a quick instrument reading and, if necessary, beam back a few bits of data.
Nonetheless, notes Priya, that
“beaming back” part continues to
be tough. “Present-generation sensors are very efficient and consume
only 50 to 100 microwatts. But a
transmitter consumes on the order
of 50 milliwatts,” he says.
To give the transmitter enough
power for its occasional bursts of
activity, the device would need to
accumulate scavenged energy in
some sort of long-lived battery. The
relatively new technology of thin-film
lithium-ion batteries is especially
appealing for such applications, says
Arms. “They are paper-thin and flexible, and they can go through an
essentially infinite number of
recharging cycles,” he says.
The final step in the energy-scavenging challenge is to integrate all
the pieces into robust, complete systems (SN: 5/5/07, p. 282).
“The long-term dream is that everything will be fabricated on
a single wafer,” says Wright. Then, the devices could be produced
en masse. Wright notes that, for example, Elizabeth Reilly of the
Berkeley group is already making such integrated devices in the
lab with MEMS processes.
The bottom line, Wright adds, is that energy-scavenging technology has a long way to go—but it is moving fast. ■
PARADISO
SHOE POWER — In an early experiment at the Massachusetts Institute of Technology, an energy scavenger built into
the sole of a running shoe harvested about 60 milliwatts of
the power a person expended while walking.
