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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.