Of the estimated 10,000 to 100,000 microbial species that inhabit our planet, scientists can coax only a few thousand to grow in the laboratory. As a result, efforts to categorize the vast diversity of microbes are lagging far behind attempts to classify plants, animals and insects. Now a report published in the current issue of the journal Science suggests that some of these so-called uncultivable microorganisms might not be so out of reach after all.
Slava S. Epstein, Kim Lewis and Tammi Kaeberlein of Northeastern University succeeded in growing pure cultures of elusive beach-growing bacteria by re-creating their shore environment in the lab. The scientists collected blocks of beach and separated the microorganisms that reside on the sandy surface into sealed chambers, which were then set atop the sediment blocks inside aquariums. Although chemicals and nutrients could enter the chambers, the bacteria remained trapped. The novel experimental setup garnered a nearly 300 percent increase in the number of microorganisms that produced colonies as compared with results achieved in conventional petri dishes. Moreover, the team isolated two previously unknown microbes, dubbed MSC1 and MSC2, and is analyzing nine others.
MSC1 [see image] and MSC2 also provided clues to why some microorganisms refuse to grow in a stark laboratory dish even when ample nutrients are supplied. The researchers discovered that culturing MSC1 and MSC2 in the specially designed chambers was easy but that the bacteria would grow in a petri dish only if both strains were present. Because bacteria can use chemicals known as pheromones to communicate, the authors conclude that "it seems possible that microorganisms require specific signals originating from their neighbors that indicate the presence of a familiar environment."