Bacteria as Multicellular Organisms

W ithout bacteria, life on earth could not exist in its present form. Bacteria are key play­ ers in many geochemical processes, including the fundamental nitrogen, carbon and sulfur cycles, which are critical to the circulation of life's basic elements. If these processes were to grind to a halt, the planet's soils, wa­ ters and atmosphere would become inhospitable for life. Yet in spite of such global importance, the notion has persisted that bacteria are simple unicellular microbes. That view is now being challenged. Investigators are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living, autonomous organism. Bacteria form complex communities, hunt prey in groups and secrete chem­ ical trails for the directed movement of thousands of individuals. Already at the beginning of this cen­ tury investigators had evidence that bacteria live communally in the soil. Martinus Beijerinck of the Netherlands discovered that Rhizobium bacteria in­ fect the roots of leguminous plants,