Anabaena sp. Strain PCC 7120 Gene devH Is Required for Synthesis of the Heterocyst Glycolipid Layer
| Autor: | Pratibha B. Hebbar, Ruanbao Zhou, C. Peter Wolk, Stephanie E. Curtis, Martha E. Ramirez |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
Nitrogen
Operon Mutant Biology Microbiology Microbial Cell Biology Glycolipid Bacterial Proteins Nitrogen Fixation Gene cluster Glycolipid transport Molecular Biology Heterocyst Anabaena Nitrogenase Gene Expression Regulation Bacterial biology.organism_classification Aerobiosis Phenotype Biochemistry Genes Bacterial Mutation Glycolipids Transcription Factors |
| Zdroj: | Journal of Bacteriology. 187:2326-2331 |
| ISSN: | 1098-5530 0021-9193 |
| DOI: | 10.1128/jb.187.7.2326-2331.2005 |
| Popis: | Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium in which, in response to deprivation for fixed nitrogen, vegetative cells at semiregular intervals differentiate into nitrogen-fixing cells called heterocysts. Nitrogenase, the enzyme that catalyzes the reduction of atmospheric dinitrogen (N2) to ammonia, is rapidly and irreversibly inactivated in the presence of oxygen. The heterocyst provides a microoxic intracellular environment for nitrogenase through the development of a thick envelope, an alteration of photosynthetic activity, and an increased rate of respiration (26). The heterocyst envelope is composed of an inner laminated glycolipid layer that greatly reduces penetration of oxygen and an outer polysaccharide layer that protects the glycolipid layer (17, 22). Studies of cyanobacterial mutants with heterocyst defects have led to the identification of a number of genes involved in the development of the heterocyst envelope. Biosynthesis of the polysaccharide layer is regulated by the products of devR (4) and hepK (28), which encode part or all of a two-component regulatory system (27). The hepA, hepB, and hepC genes are involved in the synthesis of the polysaccharide layer (14, 25, 28). Synthesis of the glycolipid layer involves a hglE gene (5) and the cluster of genes hglD, hglC, and hglB (hetM) (1, 3). The hglK (2) and devBCA gene cluster (8) are implicated in glycolipid transport and/or assembly. The devH gene was identified in a screen for sequences up-regulated during heterocyst development (6). The steady-state level of devH transcripts increases fivefold upon nitrogen starvation of Anabaena sp. strain PCC 7120. In the absence of fixed nitrogen, a devH mutant strain (A57) forms heterocysts but is incapable of fixing nitrogen in the presence of oxygen (the Fox− phenotype) (12). The DevH protein is most closely related to the cyanobacterial transcriptional regulator NtcA, with a high degree of identity in the helix-turn-helix motif presumed to be involved in DNA binding (12). The similarity of DevH and NtcA and the phenotype of the devH mutant suggest that DevH plays a role as a trans-acting regulatory protein with a role in heterocyst function. Here we provide initial characterization of DevH protein expression and show that the Fox− phenotype of the devH mutant is associated with defective heterocyst envelopes that lack the glycolipid layer. |
| Databáze: | OpenAIRE |
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