Featured Research

from universities, journals, and other organizations

Light-sensitive Protein Found In Many Marine Bacteria

Date:
February 19, 2007
Source:
Lawrence Berkeley National Laboratory
Summary:
New light has been shed on proteorhodopsin, the light-sensitive protein found in many marine bacteria. Researchers at the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley have demonstrated that when the ability to respire oxygen is impaired, bacterium equipped with proteorhodopsin will switch to solar power to carry out vital life processes.

These movie frames show a tethered E.coli cell engineered to express the proteorhodopsin protein under red and green light.
Credit: Image courtesy of Lawrence Berkeley National Laboratory

New light has been shed on proteorhodopsin, the light-sensitive protein found in many marine bacteria. Researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley have demonstrated that when the ability to respire oxygen is impaired, bacterium equipped with proteorhodopsin will switch to solar power to carry out vital life processes.

“Our research shows that proteorhodopsin contributes to a bacterial cell’s energy balance only under certain environmental conditions, namely when the cell’s ability to respire has been impaired,” said Jan Liphardt, a biophysicist who holds a joint appointment as a Divisional Fellow in Berkeley Lab's Physical Biosciences Division (PBD) and the Physics Department of UC Berkeley (UCB). “By harvesting light, proteorhodopsin enables bacterial cells to supplement respiration as a cellular energy source. This ability to withstand oxygen deprivation probably explains why so many ocean bacteria express proteorhodopsin.”

Liphardt said that the solar power option represents a potentially significant boost for efforts to develop alternatives to fossil fuel energy sources. Microbes that can simultaneously harvest energy from several different sources may be better at producing biofuels than microbes that can only utilize a single energy source.

The results of this study appear in a paper published by the Proceedings of the National Academy of Sciences (PNAS), entitled: Light-powering Escherichia coli with proteorhodopsin. Co-authoring the paper with Liphardt were UCB graduate students Jessica Walter and Derek Greenfield, and Carlos Bustamante, who also holds a joint Berkeley Lab-UCB appointment and is a Howard Hughes Medical Institute (HHMI) investigator.

There was a great deal of excitement in the biology community in 2000 when proteorhodopsin was first discovered encoded within the genomes of uncultivated marine bacteria. The discovery implied that such bacteria possessed phototrophic as well as respiratory capabilities. This would be a critical adaptation for seafaring microbes because the world’s oceans are permeated with “dead zones,” areas that lack sufficient oxygen to sustain life.

Subsequent studies established that proteorhodopsin is a light-driven proton pump, able to transport protons across cellular membranes in order to create stored electrochemical energy. In this respect, it is similar to another protein, bacteriorhodopsin, that’s used by bacteria in salt ponds to supplement respiration. However, in experiments in which marine bacteria endowed with proteorhodopsin were exposed to light, there was no response. This begged the question: What does proteorhodopsin actually do?

A recent study out of the University of Kalmar in Sweden, led by Jarone Pinhassi, showed that light could be used to stimulate the growth of some types of marine bacteria carrying proteorhodopsin. This indicated that such bacteria can use a form of photosynthesis to supplement respiration as an energy source, but the extent to which light could be used to replace respiration was still unknown.

“Our thinking was that if you had a system that could harvest energy from two different sources and you knocked out one of those sources then you would probably maximize the alternative energy source,” Liphardt said. “Think of it like a capacitor. If a capacitor is already fully charged and you connect a battery to it nothing happens. However, if you drain the capacitor and then connect a battery, a current will flow.”

To observe proteorhodopsin in action and measure its effects, Liphardt and his co-authors genetically engineered a strain of Escherichia coli that would express the light-sensitive protein.

Said Walter, “The energy metabolism of E. coli is well understood so it served as an excellent testbed for observing proteorhodopsin activity when the microbe’s ability to respire is suddenly impaired. We impaired respiration through either oxygen depletion or the respiratory poison azide.”

The Berkeley researchers monitored single cells of E. coli and observed the response to light of the proton motive force (pmf), the electrochemical potential of protons across cellular membranes that bacteria use as the energy source to, among other functions, power the rotary flagellar motor which enables them to swim.

“We found that if we shined light on our E. coli cells when their respiration was impaired, they would swim or stop depending on the light’s color,” said Walter. “Proteorhodopsin has an absorption spectrum that peaks in the green wavelengths, so the cells swam when they were exposed to green light, but stopped when they were exposed to red light.”

In the absence of the azide respiratory poison, green light had no effect on the flagellar motors of these proteorhodopsin-equipped E. coli. By measuring the pmf of individual illuminated cells under different concentrations of azide or various degrees of lighting, the Berkeley researchers were able to quantify the coupling between light-driven and respiratory proton currents. At the highest azide concentrations, the average cell velocity increased 70-percent upon green light illumination. In the control study, normal E. coli cells, which do not not express proteorhodopsin, had no response to the green light.

The next step in this work, Liphardt said, is to optimize the amount of light that can be collected in cells enhanced with proteorhodopsin. For this the researchers will need to identify the most efficient forms of the protein, then manipulate microbial genomes through the addition or deletion of key genes.

This work was supported by the U.S. Department of Energy’s Office of Science, Energy Biosciences Program, the University of California, Berkeley, the Hellman Faculty Fund, the Sloan and Searle foundations, and the National Science Foundation for Graduate Research Support.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our Website at http://www.lbl.gov.


Story Source:

The above story is based on materials provided by Lawrence Berkeley National Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

Lawrence Berkeley National Laboratory. "Light-sensitive Protein Found In Many Marine Bacteria." ScienceDaily. ScienceDaily, 19 February 2007. <www.sciencedaily.com/releases/2007/02/070210170433.htm>.
Lawrence Berkeley National Laboratory. (2007, February 19). Light-sensitive Protein Found In Many Marine Bacteria. ScienceDaily. Retrieved August 21, 2014 from www.sciencedaily.com/releases/2007/02/070210170433.htm
Lawrence Berkeley National Laboratory. "Light-sensitive Protein Found In Many Marine Bacteria." ScienceDaily. www.sciencedaily.com/releases/2007/02/070210170433.htm (accessed August 21, 2014).

Share This




More Matter & Energy News

Thursday, August 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Flower Power! Dandelions Make Car Tires?

Flower Power! Dandelions Make Car Tires?

Reuters - Business Video Online (Aug. 20, 2014) Forget rolling on rubber, could car drivers soon be traveling on tires made from dandelions? Teams of scientists are racing to breed a type of the yellow flower whose taproot has a milky fluid with tire-grade rubber particles in it. As Joanna Partridge reports, global tire makers are investing millions in research into a new tire source. Video provided by Reuters
Powered by NewsLook.com
Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Newsy (Aug. 19, 2014) Scientists have developed a new device that mimics the way octopuses blend in with their surroundings to hide from dangerous predators. Video provided by Newsy
Powered by NewsLook.com
Researcher Testing on-Field Concussion Scanners

Researcher Testing on-Field Concussion Scanners

AP (Aug. 19, 2014) Four Texas high school football programs are trying out an experimental system designed to diagnose concussions on the field. The technology is in response to growing concern over head trauma in America's most watched sport. (Aug. 19) Video provided by AP
Powered by NewsLook.com
Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

AFP (Aug. 19, 2014) A solar cell that resembles a flower is offering a new take on green energy in Japan, where one scientist is searching for renewables that look good. Duration: 01:29 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins