Structural Patterning in Bacteria May Improve Their Bioenergy Uses

patN, a gene, is required for normal heterocyst patterning.

The Science

Heterocysts, cells specialized for nitrogen fixation in certain filamentous cyanobacteria, appear singly in a nonrandom spacing pattern along the chain of vegetative cells. A two-stage, biased initiation and competitive resolution model has been proposed to explain the establishment of this spacing pattern. There is substantial evidence that competitive resolution of a subset of cells initiating differentiation occurs by interactions between a self-enhancing activator protein, HetR, and a diffusible pentapeptide inhibitor PatS-5 (RGSGR). Results presented here show that the absence of a unique membrane protein, PatN, in Nostoc punctiforme strain ATCC 29133 leads to a threefold increase in heterocyst frequency and a fourfold decrease in the vegetative cell interval between heterocysts. Researchers report the characteristics of a gene (patN) that is required for normal heterocyst patterning, and the phenotype and protein localization of which is consistent with a role in the biased initiation of heterocyst differentiation via biased inheritance.


In comparison to multicellular plants and animals, bacteria are relatively simple, typically existing as single cells. However, some bacteria cooperate to form surprisingly sophisticated structures. The photosynthetic microbe Nostoc punctiforme forms long filaments of connected cells. At regular spacing along these filaments, individual cells differentiate to form heterocysts, non-photosynthetic cells that convert nitrogen gas into biologically useful nitrogen compounds. This patterning allows these microbes to separately perform both photosynthesis (which produces O2 as byproduct) and “fix” nitrogen using enzymes that are poisoned by oxygen, cooperatively exchanging the resulting nutrients between the cell types. In a new study, U.S. Department of Energy (DOE) researchers at the University of California–Davis, describe genetic mechanisms responsible for the establishment and maintenance of this distinctive pattern in growing filaments. When the expression of a series of regulatory genes (the “pat system”) was experimentally manipulated, filaments formed with abnormal distributions of heterocysts. By analyzing these patterns and tracking the distribution of related proteins in dividing cells, the investigators were able to develop a new model describing the regulatory interactions resulting in the pattern that allows optimal photosynthesis and nitrogen fixation in the filaments. The results of this study provide valuable new insights into the mechanisms used by microbes to tune their functional attributes through the use of structural patterns and could lead to the development of new tools for optimizing processes in biological systems engineered for bioenergy applications.

BER Program Manager

Dawn Adin

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Risser, D. D., F. C. Y. Wong, and J. C. Meeks. 2012. “Biased Inheritance of the Protein PatN Frees Vegetative Cells To Initiate Patterned Heterocyst Differentiation,” Proceedings of the National Academy of Sciences (USA) 109, 15342–347. DOI: 10.1073/pnas.1207530109.