Identification of novel regulatory mechanisms controlling heterocyst development in Anabaena Sp. strain PCC 7120

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Title: Identification of novel regulatory mechanisms controlling heterocyst development in Anabaena Sp. strain PCC 7120
Author: Aldea, Maria Ramona
Abstract: The regulatory mechanisms that govern heterocyst development in Anabaena sp . strain PCC 7120 have been continuously refined over the last two decades . In this work , we show that three of the sigma factor genes present in the Anabaena sp . strain PCC 7120 genome are developmentally regulated . Time -lapse microscopy of gfp reporter strains indicated that expression of sigC , sigG , and sigE is upregulated specifically in differentiating cells at 4 h , 9 h and 16 h , respectively , after induction of heterocyst development . We proposed that the sigma factors encoded by these genes are involved in regulation of heterocyst -specific genes whose expression is relatively coincident with that of sigC , sigG , or sigE . Indeed , inactivation of the sigC gene caused delayed and reduced expression of genes required for the early stages of heterocyst development , and caused delayed development . Inactivation of the sigE gene caused a considerable drop in expression of nifH , a late gene required for nitrogen fixation . We also provide evidence that c -di -GMP , a novel bacterial second messenger , is involved in regulating heterocyst development . The all2874 gene encodes a bona fide diguanylate cyclase , which synthesizes c -di -GMP , and the gene's inactivation resulted in a decreased tendency to form heterocysts ; this phenotype was exacerbated by high light intensity . We hypothesize that the putative operon all2875 -all2874 senses and relays information about light conditions and this information is integrated into the decision to form heterocysts . Finally , we identified the all0187 gene , which is expressed at 9 h , a time when cells that have initiated differentiation commit to complete the process . In nitrogen -free medium , all0187 mutant filaments formed abnormally long heterocysts and were unable to grow diazotrophically . Septum formation between heterocysts and their flanking vegetative cells was incomplete , leaving one or both poles of the heterocysts more opened and potentially more permeable to oxygen . Despite having nitrogenase activity , the all0187 mutant was unable to grow diazotrophically . We hypothesize that the diazotrophic growth defect is caused by the inability of the heterocysts to transport fixed nitrogen to the neighboring vegetative cells .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2996
Date: 2009-05-15

Citation

Identification of novel regulatory mechanisms controlling heterocyst development in Anabaena Sp. strain PCC 7120. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2996 .

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