Abundance, Depth Distribution, and Composition of Aerobic Bacteriochlorophyll a -Producing Bacteria in Four Basins of the Central Baltic Sea

Abstract

The abundance, vertical distribution, and diversity of aerobic anoxygenic phototrophic bacteria (AAP) were studied at four basins of the Baltic Sea. AAP were enumerated by infrared epifluorescence microscopy, and their diversity was analyzed by using pufM gene clone libraries. In addition, numbers of CFU containing the pufM gene were determined, and representative strains were isolated. Both approaches indicated that AAP reached maximal abundance in the euphotic zone. Maximal AAP abundance was 2.5 ؋ 10 5 cells ml ؊1 (11% of total prokaryotes) or 1.0 ؋ 10 3 CFU ml ؊1 (9 to 10% of total CFU). Environmental pufM clone sequences were grouped into 11 operational taxonomic units phylogenetically related to cultivated members of the Alpha-, Beta-, and Gammaproteobacteria. In spite of varying pufM compositions, five clones were present in all libraries. Of these, Jannaschia-related clones were always found in relative abundances representing 25 to 30% of the total AAP clones. The abundances of the other clones varied. Clones potentially affiliated with typical freshwater Betaproteobacteria sequences were present at three Baltic Sea stations, whereas clones grouping with Loktanella represented 40% of the total cell numbers in the Gotland Basin. For three alphaproteobacterial clones, probable pufM phylogenetic relationships were supported by 16S rRNA gene analyses of Baltic AAP isolates, which showed nearly identical pufM sequences. Our data indicate that the studied AAP assemblages represented a mixture of marine and freshwater taxa, thus characterizing the Baltic Sea as a "melting pot" of abundant, polyphyletic aerobic photoheterotrophic bacteria.Aerobic bacteriochlorophyll a-producing bacteria, or so-called aerobic anoxygenic phototrophic bacteria (AAP), are strict aerobes, carrying out a photoheterotrophic metabolism. They require organic substrates for growth, but they can supplement a significant portion of their metabolic requirements by light-derived energy (8,16,26,31,39). AAP were discovered in the Bay of Tokyo by Shiba et al. (34) in 1970s. Later, their wide distribution in marine environments was documented by infrared (IR) kinetic fluorometry (16, 18), IR epifluorescence microscopy (IREM) (9,14,19,23,33) and pigment analyses (12), as well as cultivation-based (1, 15, 38) and genetic (3, 5, 13, 28, 41) studies. The planktonic bacterial assemblages are known to contain various AAP groups belonging to Alpha-, Beta-, and Gammaproteobacteria (41). Microscopic analyses have shown that AAP abundances vary in different environments from 0 to 24% of total prokaryotes (9, 21, 33).The ecological role of aerobic anoxygenic phototrophy is still unclear. A recent study suggested that AAP significantly contribute to bacterial production in oligotrophic oceans (17). Their ability to use light energy in addition to respiration could provide them an advantage over their heterotrophic bacterial relatives (2). In contrast, Schwalbach et al. (32) found no effect of light on microbial community structure. Clearly, more data on AA...

Bacteriochlorophyll and community structure of aerobic anoxygenic phototrophic bacteria in a particle-rich estuary

“…We examined AAP bacteria because they are widespread and abundant in marine environments (Cottrell et al, 2006;Sieracki et al, 2006;Salka et al, 2008), especially in estuaries such as the Chesapeake Bay (Schwalbach and Fuhrman, 2005;Waidner and Kirchman, 2007), where there is a large range of environmental conditions hypothesized to influence photoheterotrophy, including turbidity and concentrations of particulate material. Data on Abbreviation: BLAST, basic local alignment search tool.…”

“…The AAP bacteria make up 1.5-15% of total prokaryotic abundance in the coastal Pacific Ocean off California (Schwalbach and Fuhrman, 2005), in tropical and polar waters (Schwalbach and Fuhrman, 2005;Cottrell and Kirchman, 2009), in the North Atlantic Ocean (Sieracki et al, 2006) and in shelf waters of the mid-Atlantic bight and in the Pacific Ocean near Hawaii (Cottrell et al, 2006). Abundances of AAP bacteria in the brackish Baltic Sea, which is much like an estuary with a large input of freshwater (Stepanauskas et al, 2002), seem to be more similar to those found in the ocean, ranging from about 1-10% of the total prokaryotes (Salka et al, 2008).…”

Diversity of cultivated and metabolically active aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea

“…All BChl-a-containing bacteria that formed visible colonies on plates were identified phylogenetically, thus assessing cultivable diversity although AAP bacteria represented a low part of the cultivable fraction. To our knowledge, although several studies examined the cultivable diversity of marine AAP bacteria (Allgaier et al, 2003;Koblizek et al, 2003;Rathgeber et al, 2008;Salka et al, 2008), this work presents the largest collection of AAP bacteria isolated in the frame of an oceanographic cruise. All our isolates belonged to the Alphaproteobacteria.…”

Vertical and longitudinal distribution patterns of different bacterioplankton populations in a canyon‐shaped, deep prealpine lake

“…Phototrophic microbes such as picocyanobacteria (Johnson et al 2006;Zwirglmaier et al 2008;Van Den Wyngaert et al 2011), and aerobic anoxygenic phototrophs (Salka et al 2008), or rhodopsin-bearing heterotrophic bacteria (Giovannoni et al 2005;Sharma et al 2009) are usually only abundant in the photic zone of oceans and lakes. Moreover, many eukaryotic algae in the well-illuminated surface-water layers are accompanied by a distinct bacterial community thriving on phytoplankton exudates (Grossart et al 2005).…”