Genetic analyses based on chromosomal lac fusions to nitrogen fixation (nif) genes demonstrated that NifA-dependent transcriptional activation of expression of Rhodobacter capsulatus nifH and nifB1 was negatively modulated by HvrA, whereas regulation of rpoN, nifA1, and nifA2 was independent of HvrA. Expression of hvrA itself was not influenced by a mutation in ntrC, which is absolutely essential for N(2) fixation. Furthermore, HvrA accumulated to comparable levels in the presence and absence of ammonium, suggesting that the amount of HvrA in the cells does not differ under nitrogenase-repressing or -derepressing conditions. In addition, competitive gel retardation studies with HvrA-His(6) purified from R. capsulatus were carried out, demonstrating preferential binding of HvrA to the nifH promoter region.
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http://dx.doi.org/10.1111/j.1574-6968.2002.tb11429.x | DOI Listing |
Proc Natl Acad Sci U S A
February 2025
Department of Marine Microbiology and Biogeochemistry, Royal Netherlands Institute for Sea Research (NIOZ), Den Burg 1790 AB, The Netherlands.
Heterocytes, specialized cells for nitrogen fixation in cyanobacteria, are surrounded by heterocyte glycolipids (HGs), which contribute to protection of the nitrogenase enzyme from oxygen. Diverse HGs preserve in the sediment and have been widely used as evidence of past nitrogen fixation, and structural variation has been suggested to preserve taxonomic information and reflect paleoenvironmental conditions. Here, by comprehensive HG identification and screening of HG biosynthetic gene clusters throughout cyanobacteria, we reconstruct the convergent evolutionary history of HG structure, in which different clades produce the same HGs.
View Article and Find Full Text PDFAntioxid Redox Signal
January 2025
Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, Granada, Spain.
To investigate the role of the RegSR-NifA regulatory cascade in the oxygen control of nitric oxide (NO) reduction in the soybean endosymbiont . We have performed an integrated study of expression and NO reductase activity in , , , , and mutants in response to microoxia (2% O) or anoxia. An activating role of RegR and NifA was observed under anoxia.
View Article and Find Full Text PDFChem Commun (Camb)
January 2025
College of Chemistry, Baicheng Normal University, Baicheng 137018, P. R. China.
Herein, the construction of potential donor-acceptor (D-A) structures was guided using density-functional theory (DFT) calculations. The photocatalytic nitrogen fixation performance of TAPT-CHF was then experimentally determined to be 327.58 μmol g h, which was attributed to its efficient photo-induced charge separation and migration ability.
View Article and Find Full Text PDFEnviron Microbiol
January 2025
Department of Biology, University of Oxford, Oxford, UK.
Rhizobia and legumes form a symbiotic relationship resulting in the formation of root structures known as nodules, where bacteria fix nitrogen. Legumes release flavonoids that are detected by the rhizobial nodulation (Nod) protein NodD, initiating the transcriptional activation of nod genes and subsequent synthesis of Nod Factors (NFs). NFs then induce various legume responses essential for this symbiosis.
View Article and Find Full Text PDFEcotoxicol Environ Saf
January 2025
College of Tropical Agriculture and Forestry, Hainan University, Haikou 570228, China; School of Breeding and Multiplication (Sanya Institute of Breeding and Multiplication), Hainan University, Sanya 572025, China.
Soil nitrogen (N) transformations control N availability and plant production and pose environmental concerns when N is lost, raising issues such as soil acidification, water contamination, and climate change. Former studies suggested that soil N cycling is chiefly regulated by microbial activity; however, emerging evidence indicates that this regulation is disrupted by heavy metal (HM) contamination, which alters microbial communities and enzyme functions critical to N transformations. Environmental factors like soil organic carbon, soil texture, water content, temperature, soil pH, N fertilization, and redox status play significant roles in modulating the response of soil N cycling to HM contamination.
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