FEMS Microbiology Ecology, 95, 2019, fz104 doi: 10.1093/femsec/fz104 Advance Access Publication Date: 10 July 2019 Research Article RESEARCH ARTICLE Aerobic anoxygenic phototrophs are highly abundant in hypertrophic and polyhumic waters N´ ora Szab ´ o-Tugyi 1, *, Lajos V ¨ or ¨ os 1 , Katalin V.-Balogh 1 , Zolt ´ an Botta-Duk ´ at 2 , G´ abor Bern ´ at 1 ,D´ enes Schmera 1 and Bogl ´ arka Somogyi 1 1 MTA Centre for Ecological Research, Balaton Limnological Institute and 2 MTA Centre for Ecological Research, Institute of Ecology and Botany ∗ Corresponding author: MTA Centre for Ecological Research, Balaton Limnological Institute, 3. Klebelsberg Kuno Street, Tihany, 8237, Hungary. Tel: +36-87-488-244/119; Fax: +36-87-448-006; E-mail: tugyi.nora@okologia.mta.hu One sentence summary: Aerobic anoxygenic phototrophs occurrence depends on chlorophyll a and coloured dissolved organic matter in hypertrophic and polyhumic waters where AAPs are highly abundant. Editor: Gary King ABSTRACT Aerobic anoxygenic phototrophs (AAPs) are a group of photoheterotrophic bacteria common in natural waters. Here, AAP abundance and contribution to total bacterial abundance and biomass were investigated to test whether the trophic status of a lake or content of coloured dissolved organic matter (CDOM) play a role in determining AAP distribution and abundance in shallow inland lakes, with special focus on hypertrophic and polyhumic waters. Twenty-six different shallow lakes in Hungary were monitored. AAP abundance and biomass were determined by epifuorescence microscopy. The lakes exhibit a broad range of CDOM (2–7000 mg Pt L −1 ) and phytoplankton biomass (2–1200 μgL −1 chlorophyll a concentration). Very high AAP abundance (up to 3 × 10 7 cells mL −1 ) was observed in polyhumic and hypertrophic shallow lakes. AAP abundance was infuenced by phytoplankton biomass and CDOM content, and these effects were interrelated. As determined, 40 μgL −1 chlorophyll a and 52 mg Pt L −1 CDOM are threshold levels above which these effects have a synergistic relationship. Hence, the observed high AAP abundance in some soda pans is a consequence of combined hypertrophy and high CDOM content. AAP contribution was infuenced by total suspended solids (TSS) content: the success of AAP cells could be explained by high TSS levels, which might be explained by the decrease of their selective grazing control. Keywords: aerobic anoxygenic phototroph; heterotrophic bacterium; abundance; chlorophyll a; coloured dissolved organic matter; shallow lake INTRODUCTION Aerobic anoxygenic phototrophs (AAPs) are bacteriochlorophyll a (BChl a)-containing aerobic bacteria (for defnition and recent reviews, see Kobl´ ıˇ zek 2015; Yurkov and Hughes 2017). They are classifed as facultative photoheterotrophs since members of this taxonomically diverse group can both utilise organic sub- strates in darkness and conduct anoxygenic photosynthesis in the presence of light. Because of BChl a, AAPs absorb light with a wavelength of up to 900–950 nm. The absorbed addi- tional energy provides AAPs with a competitive advantage over purely heterotrophic microbes (Kobl´ ıˇ zek 2015). Wide distribution of AAP bacteria in the ocean was frst reported by Kolber et al. (2000). Since then, AAPs have been identifed in many different aquatic habitats. Nevertheless, most studies focus on marine systems (Kobl´ ıˇ zek 2015). Indeed, AAPs play an important role in aquatic ecosystems and nutrient cycling. They usually account for 10–20% of bacterioplankton biomass in marine environments (Maˇ s´ ın et al. 2006; Salka et al. 2008; Cottrell and Kirchman 2009; Received: 15 October 2018; Accepted: 8 July 2019 C  FEMS 2019. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com 1 Downloaded from https://academic.oup.com/femsec/article/95/8/fiz104/5530753 by guest on 04 November 2022