CAROTENOID COMPOSITION OF MARINE RED ALGAE1

Photosynthetic organisms possess carotenoids that function either as accessory, photoprotective, or structural pigments. Therefore, the carotenoid profile provides information about certain photoacclimation and photoprotection responses. Carotenoids are also important chemosystematic markers because specific enzymes mediate each step of carotenoid biosynthesis. For red algae, diverse and often contradictory carotenoid compositions have been reported. As a consequence, it is difficult to infer the physiological importance of carotenoids in Rhodophyta. To characterize the relationship between carotenoid composition, rhodophycean phylogeny, and the presence of potentially photoprotective pigments, we analyzed the carotenoid composition of 65 subtropical species from 12 orders and 18 rhodophyte families. Our results showed that red algae do not present a unique carotenoid profile. However, a common profile was observed up to the level of order, with exception of the Ceramiales and the Corallinales. The main difference between profiles is related to the xanthophyll that represents the major carotenoid. In some species lutein is the major carotenoid while in others it is substituted by zeaxanthin or antheraxanthin. The presence of this epoxy carotenoid together with the presence of violaxanthin that are xanthophyll cycle (XC)‐related pigments was found in four of the 12 analyzed orders. The carotenoid pigment profiles are discussed in relation to Rhodophyta phylogeny, and it is suggested that the xanthophyll cycle‐related pigments appeared early in the evolution of eukaryotic phototrophs.     

Marine fungus <Emphasis Type="Italic">Stilbella aciculosa</Emphasis> as a potential producer of prostaglandins

The amount and composition of fatty acids in the fungus Stilbella aciculosa associated with the marine macroorganism Apostichopus japonica (trepang) were determined by gas-liquid chromatography and gas chromatography-mass spectrometry. In the culture liquid of S. aciculosa, prostaglandins (PG) of groups E and F were revealed by UV spectroscopy. This finding was confirmed by the presence of direct precursors of PG, polyunsaturated eicosapentaenoic and docosahexaenoic acids, in the culture liquid. The biomass of this fungus contained PG of group B.     

Phylogeographic patterns and species delimitation in the endangered silverside “humboldtianum” clade (Pisces: Atherinopsidae) in central Mexico: understanding their evolutionary history

The Atherinopsidae is the second largest group of freshwater fishes occupying central Mexico and is one of biological, cultural, and economic importance. The “humboldtianum” clade (Genus Chirostoma) is a “species flock” of nine described species that inhabit lacustrine ecosystems in central Mexico. The high morphological polymorphism within the group makes species identification difficult and thereby limits the development of research and management projects focusing on this group. In this study, we used phylogeographic and coalescent-based methods to understand the evolution of genetic variation among these species. The results revealed taxonomic inaccuracies and genetic admixture among species. Genetic variation was structured geographically, rather than taxonomically, and five closely related genetic groups were recovered. Two evolutionary pathways were found. First, a novel geographical arrangement of haplotypes was recovered that gave rise to the five recently (Pleistocene, <?1 Myr) derived genetic groups. The second pathway showed a recent intra-lacustrine genetic differentiation that could be associated with sympatric or ecological speciation. The current classification of the group is revised and includes a reduction in the number of valid species in the “humboldtianum” clade. Moreover, this study provides new insight into the biogeography and evolutionary history of this important group of fishes.

     

Isolation and chemical characterization of algal polysaccharides from the green seaweed Ulva clathrata (Roth) C. Agardh

In order to obtain information on the content and composition of the water-soluble polysaccharides from Ulva clathrata, an extraction at 60°C, in different media, was performed: water, EDTA and HCl (F-I), each followed by a sequential extraction in NaOH 0.1 M (F-II). The extracts were recovered and analyzed for total carbohydrates, proteins, rhamnose, uronic acids and sulfate content. Differences were obtained in the yield and composition in both fractions of the different media (F-I and F-II). Higher yields resulted in the first fraction on all media. HCl extraction was the best in both fractions (14.83 ± 1.5% and 5.96 ± 1.1%, F-I and F-II, respectively). In all cases, F-I was more sulfated ranging from 27.87% to 35.8% and higher in rhamnose content, whereas F-II had higher protein and slightly higher uronic acid content. FTIR spectra showed that soluble polysaccharides from the green seaweed U. clathrata are sulfated polysaccharides, similar to ulvan obtained from other Ulva species and confirmed by the ¹ H-NMR spectrum, where the characteristic signal for the deoxy sugar (rhamnose) is present.     

Contribution of the Salmonella enterica KdgR Regulon to Persistence of the Pathogen in Vegetable Soft Rots

During their colonization of plants, human enteric pathogens, such as Salmonella enterica, are known to benefit from interactions with phytopathogens. At least in part, benefits derived by Salmonella from the association with a soft rot caused by Pectobacterium carotovorum were shown to be dependent on Salmonella KdgR, a regulator of genes involved in the uptake and utilization of carbon sources derived from the degradation of plant polymers. A Salmonella kdgR mutant was more fit in soft rots but not in the lesions caused by Xanthomonas spp. and Pseudomonas spp. Bioinformatic, phenotypic, and gene expression analyses demonstrated that the KdgR regulon included genes involved in uptake and metabolism of molecules resulting from pectin degradation as well as those central to the utilization of a number of other carbon sources. Mutant analyses indicated that the Entner-Doudoroff pathway, in part controlled by KdgR, was critical for the persistence within soft rots and likely was responsible for the kdgR phenotype.