News | September 18, 2000

Light harvest protein found in plankton

Light harvest protein found in plankton

DNA sequencing unearths novel protein that sheds new light on microbial ecology, energy, and nutrient cycling in the sea

The genomic sequence of the naturally occurring marine bacterioplankton has unearthed a new type of rhodopsin, the first light-harvesting protein found in the domain Bacteria. The presence of this activity in bacterioplankton, which is widespread throughout the marine environment, suggests that a role for it in cycling carbon in the oceans and utilizing sunlight for food production. The study, conducted jointly by researchers from Amersham Pharmacia Biotech (Sunnyvale, CA) and Monterey Bay Aquarium Research Institute (MBARI; Moss Landing, CA) is published in the September 15, 2000 issue of Science.

"We've uniquely applied new advances in genomic technology to our studies of oceanic microbes and it has lead us to unexpected results," said lead researcher Ed DeLong. "We now have the techniques to address some important ecological questions about the role of these microorganisms in the ocean."

Sample of oceanic bacteria as seen using epifluorescence microscopy. Ribosomal RNA probes developed by MBARI microbiologist Ed DeLong are used to identify specific bacteria (seen in red).

While oceanic picoplankton cannot be readily grown in culture, using new techniques, biologists at MBARI have been able to identify prominent groups of microbes in the ocean, allowing them to map their distribution and abundance. But the function of those microbes in their environment has remained unknown. DeLong and postdoctoral associate Oded Béjà have devised methods to dissect the genomes of the uncultivated microbes, allowing them to identify the functions of specific genes and predict their ecological significance.

In this recent study, samples of oceanic bacteria were collected in Monterey Bay. The MBARI researchers isolated large genome fragments and, with colleagues at Amersham Pharmacia Biotech, produced raw sequence data from the picoplankton DNA which were assembled and analyzed at MBARI to reveal the encoded genes and their hypothetical function. The oceanic microbial genome sequence revealed a new rhodopsin-like pigment never before found in any bacterial species. The bacterial sequence suggested that this new photopigment might serve as a type of light-driven ion pump, enabling the oceanic microbes to generate energy from sunlight.

MBARI researchers expressed the rhodopsin-like gene in E. coli in order to test its function. As predicted, when exposed to light, the photopigment moved ions across the cell membrane, showing that it can generate energy by absorbing light. Additional bioinformatics analysis and biophysical experiments necessary for this study were conducted by researchers from the National Center for Biotechnology Information (National Institutes of Health) and the University of Texas Medical School.

DeLong and his colleagues are excited by the many implications of this research, especially the demonstrated effectiveness of using genomics for characterizing naturally occurring microbes. Their research suggests that rhodopsin-like photopigments appear to be more taxonomically widespread than previously thought and reveals a new type of light-driven energy generation in an abundant oceanic microbial group. For nanotechnology development, this research has generated interest in the potential for new applications in the area of light-actuated molecular switches.

For more information: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039-9644. Tel: 831-775-1700.

Edited by Laura DeFrancesco
Managing Editor, Bioresearch Online

Source: Monterey Bay Aquarium Research Institute

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