Abstract
Heterocysts are specialized cells that differentiate in the filaments of heterocystous cyanobacteria. Their role is to maintain a microoxic environment for the nitrogenase enzyme during diazotrophic growth. The lack of photosynthetic water oxidation in the heterocyst puts special constraints on the energetics for nitrogen fixation, and the electron transport pathways of heterocyst thylakoids are slightly different from those in vegetative cells. During recent years, there has been a growing interest in utilizing heterocysts as cell factories for the production of fuels and other chemical commodities. Optimization of these production systems requires some consideration of the bioenergetics behind nitrogen fixation. In this overview, we emphasize the role of photosynthetic electron transport in providing ATP and reductants to the nitrogenase enzyme, and provide some examples where heterocysts have been used as production facilities.
Highlights
Oxygenic photosynthesis revolutionized life on earth by providing an endless source of energy and electrons for carbon dioxide fixation and by changing the composition of the atmosphere that enabled the development of multicellular life forms
Heterocysts differentiate from the mature vegetative cells that are actively photosynthesizing in filamentous cyanobacteria [10]
When it was shown that nitrogenase activity in isolated heterocysts can be interrupted by addition of dibromothymoquinone (DBMIB), an inhibitor of the cytochrome-b6 /f (Cyt-b6 f ) complex, it became clear that it is the heterocyst thylakoid membranes that provide the driving force for ATP-synthesis [7,35]
Summary
Oxygenic photosynthesis revolutionized life on earth by providing an endless source of energy and electrons for carbon dioxide fixation and by changing the composition of the atmosphere that enabled the development of multicellular life forms. Several cyanobacterial strains are able to fix atmospheric nitrogen into ammonia This is made by the enzyme nitrogenase, in an extremely ATP-demanding reaction: N2 + 8 H+ + 8 e− + 16 MgATP → 2 NH3 + H2 + 16 MgADP + 16 Pi. To protect the nitrogenase from being inactivated by oxygen, nitrogen fixation has to be kept separated from photosynthetic oxygen formation either spatially or temporally. Which pathway the reducing equivalents take from there before they are fed to the nitrogenase by ferredoxin is still a matter of debate [7] This question has gained in importance during the past decade, as heterocysts have become attractive candidates for being used as host compartments for oxygen-sensitive biosynthetic production [8,9]. The aim of this review is to shed some light on energy flows in the heterocyst and to indicate new research directions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
