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Genetic responses to carbon and nitrogen availability in Anabaena
Author(s) -
Herrero Antonia,
Flores Enrique
Publication year - 2019
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.14370
Subject(s) - heterocyst , biology , cyanobacteria , anabaena , nitrogen fixation , carbon fixation , photosynthesis , transcription factor , nitrogen assimilation , phototroph , promoter , microbiology and biotechnology , gene , botany , gene expression , biochemistry , genetics , bacteria
Summary Heterocyst‐forming cyanobacteria are filamentous organisms that perform oxygenic photosynthesis and CO 2 fixation in vegetative cells and nitrogen fixation in heterocysts, which are formed under deprivation of combined nitrogen. These organisms can acclimate to use different sources of nitrogen and respond to different levels of CO 2 . Following work mainly done with the best studied heterocyst‐forming cyanobacterium, Anabaena , here we summarize the mechanisms of assimilation of ammonium, nitrate, urea and N 2 , the latter involving heterocyst differentiation, and describe aspects of CO 2 assimilation that involves a carbon concentration mechanism. These processes are subjected to regulation establishing a hierarchy in the assimilation of nitrogen sources –with preference for the most reduced nitrogen forms– and a dependence on sufficient carbon. This regulation largely takes place at the level of gene expression and is exerted by a variety of transcription factors, including global and pathway‐specific transcriptional regulators. NtcA is a CRP‐family protein that adjusts global gene expression in response to the C‐to‐N balance in the cells, and PacR is a LysR‐family transcriptional regulator (LTTR) that extensively acclimates the cells to oxygenic phototrophy. A cyanobacterial‐specific transcription factor, HetR, is involved in heterocyst differentiation, and other LTTR factors are specifically involved in nitrate and CO 2 assimilation.