Seasonal changes and diversity of aerobic anoxygenic phototrophs in the Baltic Sea

Abstract

The community of aerobic anoxygenic phototrophs was investigated in the Baltic Sea using infrared epifluorescence microscopy from September 2004 to October 2005. The majority of these bacteriochlorophyll-containing organisms exhibited a specific sickle-shaped morphology, with rods or other morphotypes observed only occasionally. Aerobic anoxygenic phototrophs were observed mostly from April to September (1 to 12% of total prokaryotes), peaking in May 2005 at a concentration of up to 0.38 × 10 6 cells ml -1. This peak was associated with the later phase of the spring bloom. In the later months, the amount of phototrophic bacteria gradually declined until the beginning of the fall mixing, and remained low from November to March, contributing only 0 to 2% of total prokaryotes. A novel technique combining fluorescent in situ hybridization (FISH) and infrared epifluorescence microscopy indicated that the Baltic aerobic anoxygenic phototrophs were mostly Gammaproteobacteria, with a smaller fraction of Alphaproteobacteria. KEY WORDS: Aerobic photosynthetic bacteria · Bacteriochlorophyll a · Photoheterotrophy · Epifluorescence microscopy Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 45: [247][248][249][250][251][252][253][254] 2006 thermocline structure gradually dissolves due to the decrease in irradiance and intensified wind mixing. The autumn bloom (September-October) is dominated by cyanobacteria along with dinophytes and chlorophytes as other main contributors (Sto? et al. 2002, Wasmund & Uhlig 2003. By the end of the fall season, the water column becomes homogenous down to the halocline, with mean water temperatures of 3 to 4°C.Earlier studies suggested that Baltic primary production is mostly limited by nitrogen availability, but the activity of nitrogen-fixing cyanobacteria in the summer period may cause limitation by phosphorus (Kivi et al. 1993, Nausch et al. 2004. Knowledge of Baltic bacterioplankton dynamics pattern is fragmentary. In the coastal zone offshore of Sweden, bacterial cell numbers display a relatively simple pattern, with a minimum in winter and a maximum in summer (Hagström et al. 1979). In early spring, the bacterial community is predominantly controlled by nitrogen availability and nanoflagellate grazing (Kuupo et al. 1998). In some studies, a stimulation of bacterial growth by phosphorus was observed in late spring, whereas in summer a great stimulation was induced by the combined addition of nitrogen and phosphorus (Kivi et al. 1993).In a previous study, we surveyed the presence of AAPs in the Baltic Sea in late summer (August -September) 2003 by IR kinetic fluorometry; at that time, Bchl a concentration varied between 8 and 50 ng l -1 . Interestingly, during our next survey in April 2004, the activity of AAPs was below the detection limit of the instrument (~2 ng Bchl a l -1 ; M. Koblí=ek unpubl. data). This result suggested that the community of AAPs in the Baltic Sea undergoes seasonal changes. For this reason, we followed ...

Measuring unbiased metatranscriptomics in suboxic waters of the central Baltic Sea using a new in situ fixation system

“…Total cell numbers were determined by 4 0 ,6-diamidino-2-phenylindole (DAPI) staining as described previously (Masín et al, 2006).…”

Towards a better understanding of microbial carbon flux in the sea*

“…However, later studies have shown that AAPs are also abundant in eutrophic marine environments, such as the Baltic Sea (Koblížek et al 2005, Ma$ín et al 2006 or the Yangtze Estuary (Zhang & Jiao 2007). Clearly, the capacity to harvest light provides an abundant source of metabolic energy.…”

“…Today, it seems that AAPs are more abundant in shelf and coastal areas than in the open ocean. In spite of large differences, AAPs typically constitute only a small percentage (2 to 4%) of total prokaryotes (Cottrell et al 2006, Ma$ín et al 2006, Sieracki et al 2006, Jiao et al 2007). As pointed out by Sieracki et al (2006) and confirmed in subsequent studies, AAP bacteria are on average larger than regular heterotrophic bacteria.…”

Diversity of Arctic pelagic <i>Bacteria</i> with an emphasis on photoheterotrophs: a review

“…Kolber et al (2000) suggested that AAP bacteria might be abundant in oligotrophic oceanic regions where the capacity to harvest light energy may provide photoheterotrophs a competitive advantage over chemoheterotrophs. Later studies showed that their abundance and distribution vary greatly among oceanic regimes, suggesting that there is a broad range of potential ecological niches for these microbes (Cottrell et al, 2006;Lehours et al, 2010;Mašín et al, 2006;Sieracki et al, 2006;Yutin et al, 2007). It seems however that AAP bacteria are more abundant in shelf and coastal areas than in the open ocean (Schwalbach and Fuhrman, 2005;Sieracki et al, 2006).…”

“…Both targeted (Hu et al, 2006;Jiao et al, 2007;Lehours et al, 2010) and non-targeted (Yutin et al, 2007) diversity studies have shown that depending on the location and environment, members of either the Alpha-or Gammaproteobacteria typically dominate the marine AAP bacterial community. For example, in the Baltic and Mediterranean seas, most AAP bacteria belonged to Gammaproteobacteria Mašín et al, 2006), while in the Global Ocean Sampling (GOS) expedition, the Roseobacter-like group of Alphaproteobacteria dominated the oligotrophic AAP bacterial community (Yutin et al, 2007).…”