Science News - October 8, 2011

method doesn’t kill the cells because information is captured from the outside, on the glass plate.

Love is applying this interrogation method to ask questions that are relevant to chronic diseases such as HIV, autoim-munity, cancer and allergies. One ongoing study tracks how allergic patients become desensitized to milk allergens, measuring how the patients’ white blood cells respond to milk extracts. The study looks at how many cells are responding, what kinds of immune proteins are being produced and how much of each protein is produced by each cell.

By analyzing large numbers of single events and interactions between small groups of cells in concert, Love can spot rare types of cells and events that are linked to disease. Certain T cells and B cells found in diseases like multiple sclerosis or diabetes, for example, typically are present at rates of 1 in 10,000 to 1 in 100,000 of the circulating T cells in a blood sample, he says. Without looking at many, many cells, he wouldn’t be able to spot or study the interactions of these rare types.

“Single-cell analysis is a bit of a misnomer in the sense that you’re not really looking at one cell,” Love says. “You’re resolving to one cell, but you are needing to look at thousands, if not tens or hundreds of thousands, of cells to understand what that individual measurement looks like in relation to the rest of the distribution.”

Single microbes

Studies of cell-to-cell differences also promise to reveal new information about single-celled organisms. For a long time, biologists thought that members of a microbe colony were all basically the same, and that those cloned from a single cell, because they were genetically identical, should react to environmental challenges in the very same way.

Scientists now know that individual traits may, in fact, serve as drivers to boost the robustness and resistance of microbial populations, says Michael Konopka, a biochemical engineer at the University of Washington in Seattle. In the October

2010 issue of Nature Chemical Biology, he and coauthor Mary Lidstrom outlined how some members of a microbial colony will stop growing in times of stress, moving into a dormant state that allows them to ride out the bad conditions while their neighbors perish.

Understanding how individuals adapt to environmental conditions, such as temperature fluctuations, could help engineers find ways to boost certain types of chemical processes used in manufacturing, Konopka says. Some naturally occurring microbes, for example, may have a built-in capacity to do the chemical reactions that industrial researchers want to perform.

Others research teams are developing ways to determine the complete genetic blueprint of single-celled organisms to get insight into whole populations of cells that are otherwise difficult to study. Stanford University scientists working under the direction of Stephen Quake are plucking single cells from populations found in pond scum, soil or even plaque on teeth, to ask a seemingly simple question: Who are you?

Conventional genetic analysis techniques require a large, pure sample of the microbes, says Paul Blainey, a postdoctoral researcher in Quake’s lab. “That usually requires that you’re able to isolate the particular organism and grow up a whole huge beaker of it in the lab.” Unfortunately, the chemical reaction used to amplify tiny amounts of DNA is notoriously prone to contamination.

To get around this problem, the Stanford group is using a laser tweezer to sort individual microbes inside tiny, automated devices designed to analyze minute traces of DNA. Enclosed within this miniature lab, microbes and their DNA are safe from contaminants.

In 2007, Quake’s group analyzed the genome of a single bacterium found in dental plaque taken from a person’s mouth. This year the team turned to a less familiar class of single-celled organisms, the Archaea: Online February 22 in PLoS One, the researchers published findings on the genome of a single-celled ammonia-eater from San Francisco Bay.

Developed at the University of British
Columbia, this microchip allows the
simultaneous analysis of 300 cells.

Genetic information gleaned from an individual microbe, combined with findings on cell-to-cell differences in behavior, may provide new insights into the thousands of unknown or barely known populations found in water and soil. Such insight could in turn offer clues to how microbes act as infectious agents and how they develop resistance to antibiotics.

Despite recent gains in studying single cells and how they differ, there’s much work to be done, Allbritton says. Current techniques still allow only a small number — fewer than two dozen — of the thousands of molecular components that float around in cells to be measured at one time.

“It’s embarrassing,” she says. “We’ve
made a lot of progress, but you can see
how far we have to go.”
With such a small subset of cellular
components under study, scientists’
perception of how cells operate may be
colored by what they see, she adds. The
big push now is to develop ways to mea-
sure more of the cell’s contents, and see
how they change over time and work in
relationship to each other.