Isolated chlorosomes of several species of filamentous anoxygenic phototrophic bacteria (FAPB) and green sulfur bacteria (GSB) were examined by atomic force microscopy (AFM) to characterize their topography and biometry. Chlorosomes of Chloroflexus aurantiacus, Chloronema sp., and Chlorobium (Chl.) tepidum exhibited a smooth surface, whereas those of Chl. phaeobacteroides and Chl. vibrioforme showed a rough one. The potential artifactual nature of the two types of surfaces, which may have arisen because of sample manipulation or AFM processing, was ruled out when AFM images and transmission electron micrographs were compared. The difference in surface texture might be associated with the specific lipid and polypeptide composition of the chlorosomal envelope. The study of three-dimensional AFM images also provides information about the size and shape of individual chlorosomes. Chlorosomal volumes ranged from ca. 35 000 nm(3) to 247 000 nm(3) for Chl. vibrioforme and Chl. phaeobacteroides, respectively. The mean height was about 25 nm for all the species studied, except Chl. vibrioforme, which showed a height of only 14 nm, suggesting that GSB have 1-2 layers of bacteriochlorophyll (BChl) rods and GFB have approximately 4. Moreover, the average number of BChl molecules per chlorosome was estimated according to models of BChl rod organisation. These calculations yielded upper limits ranging from 34 000 BChl molecules in Chl. vibrioforme to 240 000 in Chl. phaeobacteroides, values that greatly surpass those conventionally accepted.

A straightforward real-time polymerase chain reaction (PCR)-based assay was designed and evaluated for the detection of Salmonella spp. in food and water samples. This new assay is based on the specific detection of the bipA gene of Salmonella, which encodes a protein of the guanosine triphosphate (GTP)-binding elongation family that displays global modulating properties, by regulating a wide variety of downstream processes. The new method correctly identified all 48 Salmonella strains used in the inclusivity test, and did not detect all 30 non-Salmonella species tested. The method was evaluated by analyzing 120 diverse food and water samples enriched in buffered peptone water. The bipA-based real-time PCR assay showed 100% efficiency, sensitivity, and specificity compared to the invA-based method previously published, which was developed as a part of a European project for the standardization of PCR methods in food microbiology. The assay includes an independent internal amplification control (IAC) in each reaction to control false negative results.

Abstract. The effects of inhibition of carotenoid biosynthesis by 2-hydroxybiphenyl on the photosynthetic growth, pigment composition and chlorosome structure of Chlorobium phaeobacteroides strain CL1401 were examined. At a concentration of 20 µg 2-hydroxybiphenyl ·ml -1 , carotenoid synthesis was largely inhibited (85%), but the photosynthetic growth rate was almost unaffected (µ control =0.00525±0.00007 h -1 and µ HBP-treated =0.00505±0.0005 h -1 ). Cells grown in the presence of the inhibitor were 5 µm-70 µm long, while control cells were between 2-5 µm long. Moreover, 2-hydroxybiphenyl-treated cells contained fewer, unevenly distributed chlorosomes per µm of cytoplasmic membrane with an irregular arrangement (2.5±1.5 vs of 9.1±1.9). This was concomitant to the 83% decrease in the content of bacteriochlorophyll (BChl) e in 2-hydroxybiphenyl-treated cells. Electron microscopy revealed that the shape of carotenoid-depleted chlorosomes changed from ellipsoidal to spherical, although the mean volume was similar to that of control chlorosomes. SDS-PAGE analysis of the chlorosome polypeptide composition showed that the amount of CsmA protein decreased by 60% in carotenoid-depleted chlorosomes. This was paralleled by a decrease in the baseplate BChl a content. The data suggest that carotenoids are close to the chlorosomal baseplate, where they carry out both structural and photoprotective functions.

The morphology (mainly prosthecae length), ultrastructure, and antenna pigment composition of the green sulfur bacterium Prosthecochloris aestuarii changed when grown under different light intensities. At light intensities of 0.5 and 5 micromol quanta m(-2) s(-1), the cells had a star-like morphology. Prosthecae, the characteristic appendages of the genus Prosthecochloris, were 232 nm and 194 nm long, respectively. In contrast, when grown at 100 micromol quanta m(-2) s(-1), these appendages were shorter (98 nm) and the cells appeared more rod-shaped. Transmission electron microscopy revealed a significant decrease in the cell perimeter to area ratio and in the number of chlorosomes per linear microm of membrane as light intensity increased. In addition to these morphological and ultrastructural responses, Prosthecochloris aestuarii exhibited changes in its pigment composition as a function of light regime. Lower specific pigment content and synthesis rates were found in cultures grown at light intensities above 5 micromol quanta m(-2) s(-1). A blue shift in the bacteriochlorophyll (BChl) c Q(y) absorption maximum of up to 17.5 nm was observed under saturating light conditions (100 micromol quanta m(-2) s(-1)). This displacement was accompanied by changes in the composition of BChl c homologs and by a very low carotenoid content. The morphological, ultrastructural and functional changes exhibited by Prosthecochloris aestuarii revealed the strong light-response capacity of this bacterium to both high and low photon-flux densities.

A population of the green sulfur bacterium Pelodictyon clathratiforme was monitored during the stratification period of Coromina Lake, a freshwater, holomictic pond of the Banyoles lacustrine area (Girona, NE Spain). The chromatographic analysis of this population revealed the presence of a wide variety of both bacteriochlorophyll (BChl) d and BChl c homologues. Isolation of chlorosomes from cultured Pelodictyon cells and their further analysis by steady‐state fluorescence indicated that, although both pigment were present in chlorosomes, only BChl c gave rise to an emission signal, suggesting a fast energy transfer from BChl d to BChl c. Likewise, chlorosomes isolated from natural samples were significantly larger (60–70 nm in width and 115–120 nm in length) than those isolated from cells grown in laboratory under optimal light conditions (48±6.8 nm and 100±15.8 nm in width and length, respectively). The potential role of heterogeneous BChl c‐ and BChl d‐containing chlorosomes and the differences in chlorosome size measured are discussed in terms of the severe light limitation (available light intensity <0.1 μmol photons m−2 s−1 at the bacterial plate) under which the population subsisted during the study period.

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