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 ...

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Phycobilins are an important group of pigments that through complementary chromatic adaptation optimize the light-harvesting process in phytoplankton cells, exhibiting great potential as cyanobacteria species biomarkers. In their extracted form, concentrations of these water-soluble molecules are not easily determined using the chromatographic methods well suited to solvent-soluble pigments. Insights regarding the quantitative spectroscopic analysis of extracted phycobilins also remain limited. Here, we present an in-depth study of two methods that utilize the spectral properties of phycobilins in aqueous extracts. The technical work was carried out using high-purity standards of phycocyanin, phycoerythrin, and allophycocyanin. Calibration parameters for the spectrofluorometer and spectrophotometer were established. This analysis indicated the possibility of detecting pigments in concentrations ranging from 0.001 to 10 μg cm−3. Fluorescence data revealed a reproducibility of 95 %. The differences in detection limits between the two methods enable the presence of phycobilins to be investigated and their amounts to be monitored from oligotrophic to eutrophic aquatic environments.

The optical properties, i.e., absorption and scattering spectra of ten strains of cyanobacteria from the Baltic Sea and Pomeranian lakes (Aphanizomenon flos-aquae KAC 15, Microcystis aeruginosa CCNP 1101, Anabaena sp. CCNP 1406, Synechocystis salina CCNP 1104, Phormidium sp. CCNP 1317, Nodularia spumigena CCNP 1401, Synechococcus sp. CCNP 1108, Nostoc sp. CCNP 1411, Cyanobacterium sp. CCNP 1105, Pseudanabaena cf. galeata CCNP 1312) grown under low light conditions were investigated. Moreover, the chlorophylls, carotenoids, and phycobilin composition as well as the size structure of chosen cyanobacteria were measured. Studied species revealed high diversity both in optical properties with the absorption spectra similarity index ranging from 0.67 to 0.94 and the pigment composition. The chlorophyll-specific absorption coefficient at 440 nm aph*(440) varied between 0.017 and 0.065 m2 mg−1. The influence of the package effect was only observed in the case of large filamentous cyanobacteria like N. spumigena or Nostoc sp. Interestingly, the package effect factor Qa*(675) for large-celled Anabaena sp. was 0.92. Besides chlorophyll a, only echinenone, β-carotene, and phycocyanin were present in all analyzed cyanobacteria strains. Zeaxanthin, which is widely used as a marker pigment for cyanobacteria, was absent in the toxic N. spumigena and Anabaena sp., which are the species that occur in the Baltic Sea most frequently causing summer cyanobacterial blooms. The investigation also showed that the sample preservation technique can introduce some major errors within the absorption band affected by the phycocyanin absorption.

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Aerobic anoxygenic phototrophs were recently found to constitute a significant portion of the marine microbial community. These bacteria use bacteriochlorophyll-containing reaction centers to perform photoheterotrophic metabolism. A new instrument for routine measurements of both chlorophyll a and bacteriochlorophyll a was used for monitoring anoxygenic phototrophs in the Baltic Sea in late summer 2003. Bacteriochlorophyll a concentration ranged from 8 to 50 ngl(-1), with an average bacteriochlorophyll/chlorophyll ratio of 4.2 x 10(-3). Moreover, diel trends in bacteriochlorophyll a signals were observed, with a distinct decline occurring during daylight hours. Based on laboratory measurements this phenomenon was ascribed to the complete inhibition of bacteriochlorophyll synthesis by light, which, in combination with a concurrent turnover of the cells, resulted in a pigment decline. Following this explanation, we postulate that bacteriochlorophyll a can serve as a natural 'pulse-and-chase' marker, allowing estimation of the mortality rates of anoxygenic phototrophs from the rates of pigment decline. Based on this assumption, we suggest that the Baltic photoheterotrophic community was characterized by high turnover rates, in a range of 0.7-2 d(-1).