The use of solar radiation by the photosynthetic bacterium, Rhodopseudomonas palustris: model simulation of conditions found in a shallow pond or a flatbed reactor.

ABSTRACT

Photosynthetic bacteria are attractive for biotechnology because they produce no oxygen and so H2 -production is not inhibited by oxygen as occurs in oxygenic photoorganisms. Rhodopseudomonas palustris and Afifella marina containing BChl a can use irradiances from violet near-UV (VNUV) to orange (350-650 nm) light and near-infrared (NIR) light (762-870 nm). Blue diode-based pulse amplitude modulation technology was used to measure their photosynthetic electron transport rate (ETR). ETR vs Irradiance curves fitted the waiting-in-line model--ETR = (ETRmax × E/Eopt) × exp (1 - E/Eopt). The equation was integrated over pond depth to calculate ETR of Afifella and Rhodopseudomonas in a pond up to 30 cm deep (A376, 1 cm = 0.1). Afifella saturates at low irradiances and so photoinhibition results in very low photosynthesis in a pond. Rhodopseudomonas saturates at ≈15% sunlight and shows photoinhibition in the surface layers of the pond. Total ETR is ≈335 µmol (e(-)) m(-2) s(-1) in NUV + photosynthetically active radiation light (350-700 nm). Daily ETR curves saturate at low irradiances and have a square-wave shape ≈11-13 mol (e(-)) m(-2) day(-1) (350-700 nm). Up to 20-24% of daily 350-700 nm irradiance can be converted into ETR. NIR is absorbed by water and so competes with the bacterial RC-2 photosystem for photons.