Genetic diversity of aerobic anoxygenic photosynthetic bacteria in open ocean surface waters and upper twilight zones
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ORIGINAL PAPER
Genetic diversity of aerobic anoxygenic photosynthetic bacteria in open ocean surface waters and upper twilight zones Yonghui Zeng · Wei Shen · Nianzhi Jiao
Received: 16 July 2008 / Accepted: 18 November 2008 / Published online: 5 December 2008 © Springer-Verlag 2008
Abstract Aerobic anoxygenic phototrophic bacteria (AAPB) represent a widespread mixotrophic bacterial group in marine ecosystems. Here we investigated AAPB genetic diversity in the surface waters and upper twilight zones of the central PaciWc, Atlantic, and Indian oceans by amplifying an AAPB marker gene (pufM, encoding photosynthetic reaction center small subunit) directly from bacterioplankton community DNA. Phylogenetic and statistical analysis of 267 pufM partial sequences in six clone libraries revealed a high diversity pattern in open ocean AAPB communities. Various AAPB subgroups belonging to Alphaand Gamma-proteobacteria were found in both surface and upper twilight zone waters. In most samples, subgroups in which no pure culture was isolated as yet were predominant. By sampling a wide size range of bacterioplankton (0.22–200 m) and introducing nested PCR to ampliWcation, we retrieved abundant pufM fragments (136 sequences in 37 OTUs) directly from upper twilight zone samples. AAPB populations in upper twilight zones covered major subgroups found in surface waters and had a slightly lower diversity, higher dominance, and lower GC and GC3 contents in pufM genes than those in surface AAPB populations. These diversity data combined with previous BChl.a data in upper twilight zones support the hypothesis that AAPB may be present below euphotic zones based on the
Communicated by M. Kühl. Y. Zeng · W. Shen · N. Jiao (&) State Key Laboratory of Marine Environmental Science, Xiamen University, Siming South Road, No. 422, Xiamen 361005, People’s Republic of China e-mail: [email protected] Y. Zeng e-mail: [email protected]
speculation that AAPB can utilize the dim light in twilight zones as a supplement to energy supply in their heterotrophic lives.
Introduction Aerobic anoxygenic phototrophic bacteria (AAPB) contain bacteriochlorophyll a (BChl.a) and represent an important functional bacterial group in marine ecosystems (Kolber et al. 2000, 2001). As heterotrophic bacteria, AAPB are actively involved in marine microbial loops and contribute to the transformation of dissolved organic matter; meanwhile, with BChl.a-based photosynthesis as a complement to their heterotrophic life (Kolber et al. 2001; Beatty 2002; Jiao et al. 2007), AAPB can use light for generation of ATP and thus reduce the consumption of organic carbon, contributing indirectly to carbon Wxation by the ocean (Jiao et al. 2006). The mixotrophic lifestyle and widespread occurrence of these photoheterotrophs in marine ecosystems are challenging our views of the carbon and energy budgets in the oceans (Eiler 2006). Since the Wrst discovery of marine AAPB isolates at the end of the 1970s in the Bay of Tokyo (Shiba et al. 1979) and the Wrst conWrmation of their high abundan
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