Na+-stimulated nitrate uptake with increased activity under osmotic upshift in Synechocystis sp. strain PCC 6803

Metabolic switching of central carbon metabolism in response to nitrate: application to autofermentative hydrogen production in cyanobacteria

Nitrate removal from culture media is widely used to enhance autofermentative hydrogen production in cyanobacteria during dark anaerobiosis. Here we have performed a systematic inventory of carbon and nitrogen metabolites, redox pools, and excreted product fluxes which show that addition of nitrate to cultures of Synechococcus sp. PCC 7002 has no influence on glycogen catabolic rate, but shifts the distribution of excreted products from predominantly lactate and H2 to predominantly CO2 and nitrite, while increasing the total consumption of intracellular reducing equivalents (mainly glycogen) by 3-fold. Together with LC-MS derived metabolite pool sizes these data show that glycogen catabolism is redirected from the upper-glycolytic (EMP) pathway to the oxidative pentose phosphate (OPP) pathway upon nitrate addition. This metabolic switch in carbon catabolism is shown to temporally correlate with the pyridine nucleotide redox-poise (NAD(P)H/NAD(P)(+)) and demonstrates the reductant availability controls H2 evolution in cyanobacteria.

Biodesalination: a case study for applications of photosynthetic bacteria in water treatment

Shortage of freshwater is a serious problem in many regions worldwide, and is expected to become even more urgent over the next decades as a result of increased demand for food production and adverse effects of climate change. Vast water resources in the oceans can only be tapped into if sustainable, energy-efficient technologies for desalination are developed. Energization of desalination by sunlight through photosynthetic organisms offers a potential opportunity to exploit biological processes for this purpose. Cyanobacterial cultures in particular can generate a large biomass in brackish and seawater, thereby forming a low-salt reservoir within the saline water. The latter could be used as an ion exchanger through manipulation of transport proteins in the cell membrane. In this article, we use the example of biodesalination as a vehicle to review the availability of tools and methods for the exploitation of cyanobacteria in water biotechnology. Issues discussed relate to strain selection, environmental factors, genetic manipulation, ion transport, cell-water separation, process design, safety, and public acceptance.