Oxygenic and anoxygenic photosynthesis in a sewage pond

Abstract

Leachate sewage ponds at Phuket Integrated Waste Management (Phuket, Thailand) are typical hypereutrophic red-water ponds found at sewage treatment plants and piggery, feedlot and poultry waste ponds with mixed communities of anoxygenic purple photosynthetic bacteria (PPB) (Bacteriochlorophyll a) and Chlorella-type green algae (Chl a + b). In vivo integrating sphere spectrometer scans (Model A&E-S90-2D, A&E Lab (UK)) showed absorbance maxima at 678–680 nm (in vivo Chl a) and a double peak at 802 and 844 nm (in vivo BChl a). High Na₂S (8.3 mol m⁻³) added to PM media selected for the PPB whereas Chlorella overwhelmed PPB in PM medium without high H₂S. Photosynthetic electron transport rate (ETR) was measured using a blue-diode-based Junior PAM (Pulse Amplitude Modulation Fluorometer) on sewage pond leachate filtered onto glass fibre disks. Diuron herbicide resistance experiments allowed measurement of both oxygenic and anoxygenic photosynthesis of a mixed population of oxygenic and anoxygenic organisms to be estimated only in special circumstances. In separate culture, the ETR vs. E curves were Chlorella-type algae, E_opt ≈ 191 ± 10 μmol quanta m⁻² s⁻¹, ETR_max = 184 ± 6.7 μmol e⁻ g⁻¹ Chl a s⁻¹; PPB, E_opt = 386 ± 15 μmol quanta m⁻² s⁻¹, ETR_max = 316 ± 7.3 μmol e⁻ g⁻¹ BChl a s⁻¹ but in a mixture of Chlorella and PPB only the oxygenic photosynthesis could be detected. In sewage pond samples, PAM rapid light curves in the presence and absence of DCMU allowed separate estimates of oxygen and anoxygenic photosynthesis to be made only if the Chl a content was very low (Chl a ≈ 0.26 μg mL⁻¹; BChl a ≈ 1.4 μg mL⁻¹). If substantial amounts of Chl a were present, fluorescence from PSII overwhelmed the signal from RC-2 of PPB, preventing the detection of anoxygenic photosynthesis. New PAM technology to measure Chl a and BChl a fluorescence separately is needed.