In-vivo turnover frequency of the cyanobacterial NiFe-hydrogenase during photohydrogen production outperforms in-vitro systems.

Cyanobacteria provide all components for sunlight driven biohydrogen production. Their bidirectional NiFe-hydrogenase is resistant against low levels of oxygen with a preference for hydrogen evolution. However, until now it was unclear if its catalytic efficiency can keep pace with the photosynthetic electron transfer rate. We identified NikKLMQO (sll0381-sll0385) as a nickel transporter, which is required for hydrogen production. ICP-MS measurements were used to quantify hydrogenase molecules per cell. We found 400 to 2000 hydrogenase molecules per cell depending on the conditions. In-vivo turnover frequencies of the enzyme ranged from 62 H2/s in the wild type to 120 H2/s in a mutant during photohydrogen production. These frequencies are above maximum in-vivo photosynthetic electron transfer rates of 47 e-/s (equivalent to 24 H2/s). They are also above those of existing in-vitro systems working with unlimited electron supply and show that in-vivo photohydrogen production is limited by electron delivery to the enzyme.

Rehabilitation of Danish veterans with spinal cord injuries during international missions.

INTRODUCTION: In the past decades, Danish soldiers have participated more frequently in combat which has resulted in an increased number of severe injuries. The aim of this study was to describe the initial treatment and rehabilitation as well as the level of function, employment, social relations, participation in leisure time activities, health, quality of life (QoL) and late complications at a follow-up in six veterans who sustained a spinal cord injury (SCI) during international military missions. METHODS: Medical records were retrieved regarding the initial treatment and rehabilitation. Questionnaires based on international experience related to SCI were used. RESULTS: The six male veterans were generally satisfied with their rehabilitation and found that they had influenced its course. All veterans had consultation with psychologists during hospitalisation, and two were advised to attend further consultations with military psychologists following discharge. The length of hospitalisation corresponded to the mean hospitalisation period for SCI patients in Denmark. At discharge, the veterans were independent with regard to clothing, toileting and mobility. All resumed work after discharge, five in the military. Satisfaction with their current work was related to whether their work skills corresponded to the work tasks at hand. Four found that their QoL was very good, one that it was satisfactory, another that it was unsatisfactory. CONCLUSION: Danish veterans with SCI were generally satisfied with their initial rehabilitation. They regained independence, and all returned to work. FUNDING: government funding via the Veteran's policy programme. TRIAL REGISTRATION: GLO-2012-10.

Hydrogen export from intertidal cyanobacterial mats: sources, fluxes and the influence of community composition.

Microbial mats from marine intertidal settings have been reported to release significant quantities of H2 , in a unique trait among other mats and microbial communities. However, the H2 source and ecophysiological mechanisms that enable its export are not well understood. We examined H2 accumulation and export in three types of greenhouse-reared mats, from the intertidal region of Guerrero Negro, Mexico, and kept under natural light-dark conditions and wetting and drying cycles simulating low-, mid- and high-tidal height periodicity. All mats released H2 reproducibly and sustainably for 1.5 years. Net H2 export took place in a pulsed daily manner, starting after dusk, and waning in the morning, as photosynthesis resumed. Mid- and low-tidal mats developed high concentrations, capable of sustaining export fluxes that represented 2-4% of the water split through primary productivity. Neither N2 fixation nor direct photolytic hydrogenogenesis was significant to this H2 export, which was fermentative in origin, variable among mats, originating from cyanobacterial photosynthate. Analyses of community composition by pyrosequencing of 16S rRNA and hoxH genes indicate that filamentous non-heterocystous cyanobacteria (e.g. Lyngbya, Microcoleus) were important in the process of H2 export, as was the relatively low abundance and activity of methanogens and sulfate reducers.

Mutagenesis of hydrogenase accessory genes of Synechocystis sp. PCC 6803. Additional homologues of hypA and hypB are not active in hydrogenase maturation.

Genes homologous to hydrogenase accessory genes are scattered over the whole genome in the cyanobacterium Synechocystis sp. PCC 6803. Deletion and insertion mutants of hypA1 (slr1675), hypB1 (sll1432), hypC, hypD, hypE and hypF were constructed and showed no hydrogenase activity. Involvement of the respective genes in maturation of the enzyme was confirmed by complementation. Deletion of the additional homologues hypA2 (sll1078) and hypB2 (sll1079) had no effect on hydrogenase activity. Thus, hypA1 and hypB1 are specific for hydrogenase maturation. We suggest that hypA2 and hypB2 are involved in a different metal insertion process. The hydrogenase activity of DeltahypA1 and DeltahypB1 could be increased by the addition of nickel, suggesting that HypA1 and HypB1 are involved in the insertion of nickel into the active site of the enzyme. The urease activity of all the hypA and hypB single- and double-mutants was the same as in wild-type cells. Therefore, there seems to be no common function for these two hyp genes in hydrogenase and urease maturation in Synechocystis. Similarity searches in the whole genome yielded Slr1876 as the best candidate for the hydrogenase-specific protease. The respective deletion mutant had no hydrogenase activity. Deletion of hupE had no effect on hydrogenase activity but resulted in a mutant unable to grow in a medium containing the metal chelator nitrilotriacetate. Growth was resumed upon the addition of cobalt or methionine. Because the latter is synthesized by a cobalt-requiring enzyme in Synechocystis, HupE is a good candidate for a cobalt transporter in cyanobacteria.