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Images: Little Things Matter A Lot

EXTRAORDINARY ORGANISMS—The cyanobacterium, Trichodesium thiebautii, form filaments (bottom image) that contain many individual disk-shaped cells, each about 15 micrometers (10-6 meters) wide. Hundreds of T. thiebautii filaments join to create a macroscopic colony about 2.0 millimeters (10-4 meters) in diameter (top image). (Photos by John Waterbury, WHOI)

BARBELL BACTERIUM—Cyanobacteria have mechanisms that allow two antagonistic physiological processes to coexist in the same organism: oxygen-producing photosynthesis and dinitrogen fixation, which is inhibited by oxygen. In Richelia (above), the two processes are separated by space: Dinitrogen fixation occurs only in the bulbous, specialized cells (heterocysts) at the end of a 60-micrometer-long, filamentous cyanobacterium. (Photo by John Waterbury, WHOI)

The cyanobacterium Trichodesium erythraeum forms filaments (top) made up of many cylindrical cells, each about 9 micrometers (10-6 meters) wide. Hundreds of filaments form a raft-shaped colony of Trichodesium erythraeum several millimeters (10-4 meters) long (bottom). The raft is colored red because the cyanobacteria contain the red light-harvesting pigment, phycoerythrin. In calm weather, buoyant colonies rise to the surface in massive blooms that can cover thousands of square kilometers. These blooms gave the Red Sea its name. (Photos by John Waterbury, WHOI)

THE INSIDE STORY—Richelia are cyanobacteria that live symbiotically inside single-celled marine plants called diatoms. The cyanobacteria have specialized dinitrogen-fixing cells that provide nitrogen to their hosts. Top: a light micrograph of the diatom Hemiaulus sp. Bottom: an epifluorescence light micrograph of the same cells, showing the red chloroplasts of the diatom and the orange fluorescence of the barbell-shaped endosymbiotic Richelia. (Photo by Dave Caron, Woods Hole Oceanographic Institution)