Upregulation of Hox-hydrogenase gene expression by nutrient adjustment in the filamentous non-heterocystous cyanobacterium Arthrospira sp. PCC 8005

Arthrospira sp. PCC 8005 is potentially able to produce hydrogen catalysed by hox gene–encoded bidirectional hydrogenase with the aid of hyp gene–encoded accessory proteins. In the present study, we investigated the physiological factors affecting the hoxE, hoxY, hoxH, and hypF transcription in Arthrospira sp. PCC 8005. About a 4-fold increase of biomass and chlorophyll-a content was observed in cells grown for 7 days in Zarrouk’s medium supplemented with Fe2+. Cells grown in N-deprived medium with added Ni2+ had increased H2 production and hydrogenase activity with a maximal value of 7.24 ± 0.25 μmol H2 mg−1 Chla h−1 and 0.61 ± 0.03 μmol H2 mg−1 Chla h−1, respectively. RT-PCR analysis revealed that cells grown in the N-deprived medium supplemented with Fe2+ or Ni2+ increased hoxE, hoxY, and hoxH transcripts. However, the highest increase of the hoxE, hoxY, hoxH, and hypF transcripts was observed in cells grown in the S-deprived medium supplemented with a combination of Fe2+ and β-mercaptoethanol. These results indicated that the increased expression of hox genes in Arthrospira sp. PCC 8005 can be achieved by proper adjustment of the nutrients in the growth medium. Phylogenetic analysis revealed that the small hydrogenase subunit, HoxY sequence, from Arthrospira sp. PCC 8005 was clustered together along with other cyanobacterial HoxY which is highly related to Arthrospira platensis NIES46.