A centimeter-long bacterium with DNA contained in metabolically active, membrane-bound organelles.

Cells of most bacterial species are around 2 micrometers in length, with some of the largest specimens reaching 750 micrometers. Using fluorescence, x-ray, and electron microscopy in conjunction with genome sequencing, we characterized Candidatus (Ca.) Thiomargarita magnifica, a bacterium that has an average cell length greater than 9000 micrometers and is visible to the naked eye. These cells grow orders of magnitude over theoretical limits for bacterial cell size, display unprecedented polyploidy of more than half a million copies of a very large genome, and undergo a dimorphic life cycle with asymmetric segregation of chromosomes into daughter cells. These features, along with compartmentalization of genomic material and ribosomes in translationally active organelles bound by bioenergetic membranes, indicate gain of complexity in the Thiomargarita lineage and challenge traditional concepts of bacterial cells.

Cytogenetic characterization of the Antarctic silverfish Pleuragramma antarctica (Boulenger 1902) through analysis of mitotic chromosomes from early larvae.

This paper describes the cytogenetic features of the Antarctic silverfish Pleuragramma antarctica (Boulenger 1902), a keystone species of the Antarctic coastal marine ecosystem. Conventional cytogenetic analyses and physical mapping of repetitive DNA sequences were performed on metaphase plates obtained through direct chromosome preparation from P. antarctica early larvae. The Antarctic silverfish have a diploid number (2n) = 48, and a karyotype made up of a majority of two-armed chromosomes (karyotype formula36m/sm + 10st + 2a, fundamental number = 94). Major ribosomal gene repeats were detected on three chromosome pairs (20, 21, and 23), in correspondence of dim DAPI stained regions. Long Interspersed Nuclear Elements (LINEs) were abundant and wide spread over all chromosomes. Overall, the cytogenetic data presented herein are consistent with a long independent cytogenetic and evolutionary history for the species. The large number of two-armed chromosomes, indicative of highly-rearranged karyotype, coupled with a diploid number of 48, a presumed primitive character for this fish group, and the spread of the major ribosomal genes on three chromosome pairs, make the Antarctic silverfish distinct from all other notothenioid species.

First description of a new uncultured purple sulfur bacterium colonizing marine mangrove sediment in the Caribbean: Halochromatium-like PSB from Guadeloupe.

Here, we report the first description of a marine purple sulfur bacterium (PSB) from sulfide-rich sediments of a marine mangrove in the Caribbean. TEM shows that this new isolate contains intracytoplasmic vesicular membrane systems (containing bacteriochlorophyll a) and larger internal sulfur granules, confirmed by EDXS analyses performed using ESEM. The sulfur distribution and mapping obtained for this PSB strain has allowed us to conclude that elemental sulfur is formed as an intermediate oxidation product and stored intracellularly. SEM shows that the bacterial cells are ovoid and extremely motile via lophotrichous flagella. Phylogenetic characterization, based on the analysis of 16S rDNA and functional gene pufM sequences, demonstrate that this strain belongs to the Chromatiaceae and may be a representative of a new species of the genus Halochromatium. Thus, reduced sediments of marine mangrove represent a sulfide-rich environment that sustains the development of Chromatiaceae, in addition to sulfur-oxidizing bacteria and cyanobacteria, as previously reported.

Description of new filamentous toxic Cyanobacteria (Oscillatoriales) colonizing the sulfidic periphyton mat in marine mangroves.

In this multidisciplinary study, we combined morphological, physiological, and phylogenetic approaches to identify three dominant water bloom-forming Cyanobacteria in a tropical marine mangrove in Guadeloupe (French West Indies). Phylogenetic analysis based on 16S rRNA gene sequences place these marine Cyanobacteria in the genera Oscillatoria (Oscillatoria sp. clone gwada, strain OG) or Planktothricoides ('Candidatus Planktothricoides niger' strain OB and 'Candidatus Planktothricoides rosea' strain OP; both provisionally novel species within the genus Planktothricoides). Bioassays showed that 'Candidatus Planktothricoides niger' and 'Candidatus Planktothricoides rosea' are toxin-producing organisms. This is the first report of the characterization of Cyanobacteria colonizing periphyton mats of a tropical marine mangrove. We describe two novel benthic marine species and provide new insight into Oscillatoriaceae and their potential role in marine sulfide-rich environments such as mangroves.

Comparative ecophysiology and genomics of the toxic unicellular alga Fibrocapsa japonica.

Summary *Ten axenic cultures, referred to as Fibrocapsa japonica, were studied for their morphology, pigment composition, toxicity and phylogeny. *Morphologically, all 10 accessions were similar and displayed equivalent pigment contents. We identified chlorophylls a and c, beta-carotene and fucoxanthin as the dominant pigments, together with xanthophyll cycle carotenoids likely to be involved in photoprotection. *All 10 accessions caused brine shrimp, Artemia salina, mortality and displayed haemolytic and haemaglutination activities toward sheep erythrocytes. Our results indicate that haemaglutination activity is a key component of F. japonica toxicity. *Examination of a collection of F. japonica expressed sequence tags (ESTs) has led to the identification of candidate genes involved in F. japonica toxicity and/or growth control.

NblA gene expression in Synechocystis PCC 6803 strains lacking DspA (Hik33) and a NblR-like protein.

Cyanobacteria respond to nutrient-limiting conditions by degrading their phycobilisomes (PBS), the light-harvesting complexes for photosynthesis. In Synechococcus sp. PCC 7942, the expression of nblA, an essential gene in this process, is controlled by the response regulator NblR and the sensor NblS. Here we study the effect of inactivation of dspA (an nblS homologue) and an nblR-like gene on phycobilisome degradation in Synechocystis sp. PCC 6803, under nitrogen starvation. In each mutant, the expression of nblA was found to be unaffected and sequential PBS degradation occurred after nitrogen deprivation (although it was slightly delayed). Our results demonstrate that dspA and nblR-like do not exert a major control of PBS degradation in Synechocystis sp. PCC 6803.

The alveolar macrophage: the Trojan horse of Bacillus anthracis.

Bacillus anthracis, the causative agent of anthrax, has a particular strategy for invading the host and crossing the alveolar barrier. B. anthracis survives within alveolar macrophages, after germination within the phagolysosome, then enters the external medium where it proliferates. Recent data have shown that edema toxin and lethal toxin are the major genetic determinants mediating the survival of germinated spores within macrophages. Here, recent advances in the analysis of B. anthracis pathogenesis are summarized and future challenges discussed.