Diurnal expression of hetR and diazocyte development in the filamentous non-heterocystous cyanobacterium Trichodesmium erythraeum

Abstract

The marine non-heterocystous cyanobacteriumTrichodesmiumfixes atmospheric N2aerobically in light.In situimmunolocalization/light microscopy of NifH revealed that lighter, non-granulated cell regions observed correspond to the nitrogenase-containing diazocyte clusters inTrichodesmiumIMS101. The number of diazocyte clusters per trichome varied from 0 to 4 depending on trichome length. The constant percentage of diazocytes (approx. 15 %) in cultured strains and five natural populations suggests a developmentally regulated differentiation process. Real-time RT-PCR showed thatntcA, encoding the global nitrogen regulator in cyanobacteria, andhetR, the key regulatory gene in heterocyst differentiation, are both constitutively expressed during a 12 h/12 h light/dark cycle.hetRin addition showed a distinct peak in the dark (close to midnight) whilenifHexpression commenced 6–8 h later. The expression of all three genes was negatively affected by addition of ammonia. Some early heterocyst differentiation genes were also identified in the genome ofTrichodesmium. The data suggest thathetRandntcAmay be required for development and function of diazocytes inTrichodesmium.