Hydrogen Photoproduction by Immobilized N ₂ -Fixing Cyanobacteria: Understanding the Role of the Uptake Hydrogenase in the Long-Term Process

Abstract

We have investigated two approaches to enhance and extend H 2 photoproduction yields in heterocystous, N 2 -fixing cyanobacteria entrapped in thin alginate films. In the first approach, periodic CO 2 supplementation was provided to alginate-entrapped, N-deprived cells. N deprivation led to the inhibition of photosynthetic activity in vegetative cells and the attenuation of H 2 production over time. Our results demonstrated that alginate-entrapped ⌬hupL cells were considerably more sensitive to high light intensity, N deficiency, and imbalances in C/N ratios than wild-type cells. In the second approach, Anabaena strain PCC 7120, its ⌬hupL mutant, and Calothrix strain 336/3 films were supplemented with N 2 by periodic treatments of air, or air plus CO 2 . These treatments restored the photosynthetic activity of the cells and led to a high level of H 2 production in Calothrix 336/3 and ⌬hupL cells (except for the treatment air plus CO 2 ) but not in the Anabaena PCC 7120 strain (for which H 2 yields did not change after air treatments). The highest H 2 yield was obtained by the air treatment of ⌬hupL cells. Notably, the supplementation of CO 2 under an air atmosphere led to prominent symptoms of N deficiency in the ⌬hupL strain but not in the wild-type strain. We propose that uptake hydrogenase activity in heterocystous cyanobacteria not only supports nitrogenase activity by removing excess O 2 from heterocysts but also indirectly protects the photosynthetic apparatus of vegetative cells from photoinhibition, especially under stressful conditions that cause an imbalance in the C/N ratio in cells.

Screening native isolates of cyanobacteria and a green alga for integrated wastewater treatment, biomass accumulation and neutral lipid production

“…Employment of isolates native to a particular area may be advantageous in their inherent suitability to environmental conditions; a potential benefit in developing an energetically efficient biofuel production platform. We have already studied the biohydrogen photoproduction of isolates from the UHCC [19], and the extension and stabilization of production through improved light conversion efficiency of cells entrapped in thin alginate films [20,21]. We expect that native isolates may have an advantage at lower bioreactor temperatures and under lower light conditions.…”

A novel Ca2+-binding protein influences photosynthetic electron transport inAnabaenasp. PCC 7120

“…Nitrogenase activity was determined using the acetylene reduction assay described by [38]. 5 ml liquid cultures grown in 3% CO2 in BG11AC or BG110C (for nitrogen-fixing conditions) were flushed with argon for 20 min and incubated in 23 ml vials with 10% acetylene in the headspace for 20 h, under 50 μmol photons m -2 s -1 light at 30°C with gentle agitation (120 rpm).…”

Produção de hidrogênio por <i>Chlamydomonas </i>spp. e <i>Anabaena</i> spp.

“…As algas possuem rápido crescimento quando adaptadas ao ambiente, podendo dobrar sua densidade dentro de horas quando se encontram nas condições ideias de crescimento, até mesmo em sistemas de fotobiorreatores fechados (RAZEGHIFARD, 2013 (TAMAGNINI et al, 2000;SCHUTZ et al, 2004;MARQUES et al, 2011;KOSOUROV et al, 2014), embora há desenvolvimento de estudos também com 1444 (referenciada também como ATCC 29413) (TAMAGNINI et al, 2000;LIU et al, 2006;BERBEROGLU et al, 2008;MARKOV et al, 2015), comprovando que são cepas produtoras de hidrogênio pelas vias de hidrogenase (biofotólise direta) e nitrogenase (biofotólise indireta).…”

“…A presença e ativação da nitrogenase são comprovadas pela redução do acetileno (C 2 H 2 ) à etileno (C 2 H 4 ) (STEWART; PEARSON, 1970;HOUCHINS, 1984;TSYGANKOV et al, 1997;KOSOUROV et al, 2014).…”

“…Além desta perspectiva futura, veem-se também esforços na engenharia genética em desenvolver cepas com mutações genéticas, analisando-se as vantagens e desvantagens, para tornar a hidrogenase menos sensível ao oxigênio (GODAUX et al, 2013;GHIRARDI, 2015;GHIRARDI, 2015), aumento da taxa respiratória para acelerar o processo de anaerobiose (XU et al, 2014) e mutações na hidrogenase de captação das cianobactérias para diminuir o efeito da reciclagem de hidrogênio produzido pela nitrogenase (MARQUES et al, 2011;TIWARI;PANDEY, 2012;KOSOUROV et al, 2014). …”