Abstract

Non-sulfur purple bacteria (NSPB) are able to grow photoheterotrophically under supplies of carbon, nitrogen and light, and produce polyhydroxyalkanoates (PHAs) and molecular hydrogen (H₂). PHAs are polyesters insoluble in water, with thermoplastic and biodegradable properties and stored as intracellular granules, and its production by NSPB would be an advantage as an eco-efficient technology, where sunlight energy and CO₂ or residual organic acids could be converted directly to the polymer. The light photons absorbed by the photosynthetic complexes of NSPB can be converted into proton gradients to be used in production of ATP (adenosine triphosphate), and this is required for another enzymatic complex, i.e., the nitrogenase, which can reduces the molecular nitrogen (N₂), or, when the environment does not present it, only H₂ is produced by such bacteria. Thus, under short wavelengths, more light energy is available for them, and more hydrogen can be produced. This study evaluate the influence of the quality/quantity of light, and the carbon/nitrogen sources concentration, on the production of PHAs granules and H₂ by a NSPB (Gram negative rod) isolated from effluent from pig slaughterhouse. Two different lamps were used - a tungsten/halogen light of 2000 lux, in the ranges of 350-400 and 550-600 nm, and another LED (warm white, 3000 K), with 3500 lux of light in the range of 350 - 680 nm. At different time intervals of incubation (0- 240 h, batch, 120 rpm, 30ºC), the pH, biomass (through microscopic counting, as total cell numbers and as mg dried weight), concentration of H₂ (gas chromatrography), acetate, lactate, formate, propionate (high performance liquid chromatography), and the presence of PHA granules (transmission electron microscopy), were monitored. The profile of carotenoids, after centrifugation of culture and biomass extraction with apolar solvents was obtained by thin-layer chromatography and quantified by spectrophotometry/HPLC. It was observed that: 1) a poor source of nitrogen was required to PHAs and H₂ production when 30 mM acetate was used as the only carbon source; 2) at low light intensities of lower wavelenght light, the PHAs, H₂ and carotenoid production significantly decreases, and biomass growth moderately, but the opposite happens with LED light; 3) after a 48-96 h under LED light, the synthesis of PHAs granules was intense, but the H₂ production was more intense after 120 h, when less and lower PHAs granules were detected.