TECHNOLOGY FOCUS - BIOLOGY - Preferred Microorganism: The photosynthetic microorganism is a recombinant organism that expresses at least one heterologous gene that produces the volatile hydrocarbon. When the volatile hydrocarbon product is isoprene, the microorganism expresses an isoprene synthase gene, and is cyanobacteria, or green microalgae. Preferred Method: The volume ratio of the gaseous phase to the aqueous phase is (1:9 to 9:1, preferably 4:6 to 6:4). The step of introducing additional CO2 into the upper gaseous phase occurs when the CO2 concentration is below 50%. When the volatile product is isoprene, the step of collecting the volatile product involves passing the contents of the gaseous phase displaced by the additional CO2 or displaced by a stream of air, through a cooled condenser and through a cooled hydrophobic solvent, to retain the isoprene and separating it from the photosynthetically-generated O2.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The hydrophobic solvent comprises methanol, ethanol, butanol, hexane, heptane, octane, or dodecane. EXAMPLE - Diffusion-based CO2 uptake, assimilation, and isoprene production in gaseous/aqueous two-phase photobioreactors by photosynthetic cyanobacteria, was carried out as follows. Substitution of PsbA2 gene with Synechocystis codon-optimized kudzu IspS gene construct (SklspS) was implemented by double homologous recombination as described in Lindberg et al, 2010. Segregation of Synechocystis DNA copies (homoplasmy) was achieved upon cultivation of transformants for several generations under antibiotic selective pressure, which promoted deletion of wild type copies of Synechocystis DNA and replacement with IspS transgene-containing copy. DNA copy homoplasmy was tested by absence of wild-type copies of PsbA2 locus in four randomly selected transformant lines. Genomic DNA PCR analysis was undertaken with primers designed to upstream and downstream regions of PsbA2 gene. This amplified larger product in transformant than in wild type corresponding to replacement of endogenous 1083 base pair PsbA2 with larger 1718 base pair SklspS gene fused to 836 base pair NptI kanamycin-resistance cassette. Cultivation of wild type and SklspS transformants under conditions of gaseous/aqueous two-phase bioreactor was carried out for production and accumulation/sequestration of isoprene hydrocarbons in culture headspace, as follows. The gaseous headspace of bioreactor was filled with 100% CO2, followed by sealing of culture and incubation under photosynthesis conditions for 48 hours. Analysis of accumulated reactor headspace gases in wild type showed no evidence of isoprene hydrocarbons. The headspace of SklspS transformant showed substantial isoprene accumulation. Thus, isoprene was sole short-chain volatile hydrocarbon generated by photosynthesis in transformant (compared with isoprene standard). The SklspS transgene and its encoded isoprene synthase enzyme were found to be responsible for catalysis of isoprene production in transformant strains. Administration of single dose of 100% CO2 was carried out as follows. A 1-liter fed-batch bioreactor was employed, where single 500 ml dose of 100% CO2 was dispersed upon bubbling slowly through 700 ml aqueous culture volume. The CO2 gas displaced other gases from headspace of bioreactor, and upon subsequent sealing of vessel, CO2 was taken-up and assimilated in photosynthesis, leading to autotrophic biomass accumulation and isoprene production by Synechocystis. Exchange of CO2 in headspace for molecular oxygen and isoprene maintained equilibrium of gas pressure in sealed headspace. When single dose of 100% CO2 was fed to cells at OD at 730 nm of 0.5, cell growth and biomass accumulation was supported for 48 hours in both wild-type and SklspS transformant cultures. After 48 hours of growth, CO2 supply was depleted from headspace and from liquid medium of culture, and cells entered stationary phase of growth. Isoprene concentration measurements from such fed-batch SklspS cultures only showed that yield of over 100 mg isoprene L-1 culture could be achieved from single dose of CO2. The initial rate of isoprene production was 2 mu g isoprene L-1 culture hour-1 and it occurred during initial 48 hours of exponential cell growth, with rate of isoprene production slowing gradually as cells entered stationary growth phase. But, isoprene accumulation continued well into stationary phase of culture, lasting for 150 hours after initiation of CO2 diffusion-based photoautotrophic growth process in fed-batch bioreactor. This observation suggested that metabolic activity continued through stationary phase of cells, and although net biomass increase was no longer observed, internal cellular metabolism was sufficient to sustain isoprene production for extended periods of time. Repetitive administration of 100% CO2 dosage was then carried out as follows. Entry into stationary phase of growth at 48 hours after administration of single dose of CO2 was found to be due to efficient diffusion-based uptake and assimilation of CO2 from culture headspace, leading to CO2 depletion in bioreactor. This interpretation was supported by recovery of growth upon repetitive administration of equivalent amounts of CO2 into reactor that invariably alleviated growth inhibition. A 500 ml dose of 100% CO2 then administered every 48 hours, and growth and productivity parameters were measured. Isoprene concentration measurements from such fed-batch SklspS cultures upon periodic supplementary administration of CO2 showed yield of 150 mg isoprene L-1 culture, and kinetics of isoprene accumulation matched kinetics of cell growth. Coupled with extended exponential growth phase was prolonged period of maximal isoprene production, where 100 mu g isoprene L-1 culture was achieved after only 70 hours of growth. Further, cultures were fed CO2 every 24 hours to support high photoautotrophic growth rates, and in addition were diluted with fresh growth medium every 48 hours, down to OD at 730 nm of 0.5. Using this approach, constant rate of isoprene production of 2 mu g isoprene L-1 culture hour-1 was achieved over 192 hours of experimentation. Photosynthetically generated isoprene and O2 were then periodically flushed out of culture headspace upon slow bubbling with aliquots of 100% CO2. The mixture of gasses from headspace were then passed through Graham condenser cooled to 4 degrees C, followed by passage of condensed isoprene (boiling point 34.1 degrees C) and other gasses through organic solvent. The mini-scale-up cultures were sealed each time after briefly bubbling with 100% CO2 to refill headspace, and culture growth resumed under constant illumination of 150 mu mol photons m-2.second-1 at 35 degrees C under gentle stirring to allow mixing and CO2 diffusion-supported photoautotrophic growth.