( n genes. Fixing N2 requires a lot of...)Hot-spring bacteria flip a metabolic switch

Fixing N2 requires a lot of energy, which raises another problem for Synechococcus. When photosynthesis shuts down at night, the mat becomes oxygen starved, making it difficult to perform respiration--an efficient energy-generating pathway that requires O2 to release the energy stored in sugars. Instead, the cells must rely on fermentation--a less efficient energy-generating pathway that can proceed without oxygen. Steunou and colleagues found that at night, Synechococcus turns on genes for specific fermentation pathways that release energy from polyglucose, which probably powers N2 fixation.

"These results add to our understanding of microbial mats as complex, integrated communities that are exquisitely adapted to life in the tough hot spring environment," Grossman commented. "There may be several different organisms living in a given mat, but it seems that they are engaging in community metabolism that changes depending on the time of day. Perhaps it is more correct to consider the mat as a single functional unit rather than as a group of individual organisms."