The microbial richness of the biosphere is large, and yet the accessible, cultivable fraction is low, less than 1%. This remarkable gap, ‘The Great Plate Count Anomaly’, was noted at the dawn of microbiology and researched by the finest microbiologists of the past, but has not been closed. The implication is that after nearly two centuries of microbiology as a science, we know remarkably little about the overwhelming part of microbial diversity on our planet.
Accessing this missing diversity is important for two key reasons: it likely plays significant roles in the function of the biosphere, and quite possibly represents an untapped mine of novel bioactive compounds. Not surprisingly, learning the nature of the ‘missing’ diversity is widely recognized as one of the most important challenges facing microbiology.
This review covers recent findings about the nature of ‘uncultivable’ microbial diversity, aiming to provide at least a partial explanation for the phenomenon.
The phenomenon of microbial uncultivability. (2013) Curr Opin Microbiol. pii: S1369-5274 (13) 00145-8. doi: 10.1016/j.mib.2013.08.003
Most of the microbial diversity on our planet cannot be cultivated, and remains inaccessible. To bring the missing species into culture, microbiologists have introduced over the past decade a number of innovations aiming to meet the demands of new microbes and better mimic their natural conditions. This resulted in a significant increase in microbial recovery yet the real reasons why so many microbes do not grow on artificial media remain largely unknown. The recently proposed scout model of microbial life cycle may provide a partial explanation for the phenomenon. It postulates that transition from dormancy to activity is a stochastic process originating in noise-driven bistability. The model helps explain several otherwise perplexing observations, and informs the future cultivation efforts.