title: Increased heterocyst frequency by patN disruption in Anabaena leads to enhanced photobiological hydrogen production at high light intensity and high cell density.
abstract: The effects of increasing the heterocyst-to-vegetative cell ratio on the nitrogenase-based photobiological hydrogen production by the filamentous heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 were studied. Using the uptake hydrogenase-disrupted mutant (ΔHup) as the parent, a deletion-insertion mutant (PN1) was created in patN, known to be involved in heterocyst pattern formation and leading to multiple singular heterocysts (MSH) in Nostoc punctiforme strain ATCC 29133. The PN1 strain showed heterocyst differentiation but failed to grow in medium free of combined-nitrogen; however, a spontaneous mutant (PN22) was obtained on prolonged incubation of PN1 liquid cultures and was able to grow robustly on N2. The disruption of patN was confirmed in both PN1 and PN22 by PCR and whole genome resequencing. Under combined-nitrogen limitation, the percentage of heterocysts to total cells in the PN22 filaments was 13-15 and 16-18% under air and 1% CO2-enriched air, respectively, in contrast to the parent ΔHup which formed 6.5-11 and 9.7-13% heterocysts in these conditions. The PN22 strain exhibited a MSH phenotype, normal diazotrophic growth, and higher H2productivity at high cell concentrations, and was less susceptible to photoinhibition by strong light than the parent ΔHup strain, resulting in greater light energy utilization efficiency in H2production on a per unit area basis under high light conditions. The increase in MSH frequency shown here appears to be a viable strategy for enhancing H2productivity by outdoor cultures of cyanobacteria in high-light environments.
authors.affiliation: The OCU Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, 558-8585, Japan. masukawa@ocarina.osaka-cu.ac.jp.
authors.forename: Hajime
authors.initials: H
authors.lastname: Masukawa
authors.affiliation: Research Institute for Photobiological Hydrogen Production, Kanagawa University, Hiratsuka, Kanagawa, 259-1293, Japan.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Sakurai
authors.affiliation: Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA.|Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Hausinger
authors.affiliation: Research Institute for Photobiological Hydrogen Production, Kanagawa University, Hiratsuka, Kanagawa, 259-1293, Japan.|Department of Biological Sciences, Kanagawa University, Hiratsuka, Kanagawa, 259-1293, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Inoue
mesh_terms: D000114:Acetylene / Q000378:metabolism; D017033:Anabaena / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006859:Hydrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology; D009591:Nitrogenase / Q000378:metabolism; D046937:Nostoc / Q000378:metabolism; D058433:Photobioreactors / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D006859:Hydrogen; D009591:Nitrogenase; D000114:Acetylene
keywords: Anabaena; Cyanobacteria; Heterocyst; Hydrogen production; Nitrogenase; patN