DSpace Angular :: Browsing by Author "Correa, Juan A."

Browsing by Author "Correa, Juan A."

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CHANGES IN BACTERIAL COMMUNITY STRUCTURE ASSOCIATED WITH COASTAL COPPER ENRICHMENT
(SOC ENVIRONMENTAL TOXICOLOGY & CHEMISTRY-SETAC, 2008) Moran, Ana C.; Hengst, Martha B.; De la Iglesia, Rodrigo; Andrade, Santiago; Correa, Juan A.; Gonzalez, Bernardo
Marine bacterial communities isolated from the water column, sediment, the rock surface, and the green seaweed Ulva compressa were studied in an intertidal ecosystem. The study area included a coastal zone chronically affected by copper mine waste disposals. Bacterial community composition was analyzed by terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes, and multivariate analyses of T-RFLP data sets were used for comparisons. Results showed that diversity and richness indexes were not able to detect differences among compartments. However, comparisons within the same compartment clearly showed that copper enrichment was associated with changes in the composition of the bacterial communities and revealed that the magnitude of the effect depends on the compartment being considered. In this context, communities from sediments appeared as the most affected by copper enrichment. The present study also demonstrated that intertidal bacterial communities were dominated by Gammaproteobacteria, Firmicutes, and Actinobacteria and the changes in these communities were mainly due to changes in their relative abundances.
Differential ecological responses to environmental stress in the life history phases of the isomorphic red alga Gracilaria chilensis (Rhodophyta)
(2013) Guillemin, Marie-Laure; Sepulveda, Roger D.; Correa, Juan A.; Destombe, Christophe
In order to better understand the alternation of generations that characterizes haploid-diploid life cycles, we assessed the existence of ecological differences between the two phases (haploid gametophyte and diploid tetrasporophyte) in Gracilaria chilensis, a rhodophyte with a typical Polysiphonia-type life cycle. We investigated the effect of light intensity and salinity on viability and growth of both phases at different ontogenetic stages: juveniles and adults. In our study, the survival of juvenile gametophytes (n) was higher than the survival of juvenile tetrasporophytes (2n) despite culture conditions; however, low salinity had greater effect on carpospores (2n) than on tetraspores (n). On the other hand, a complex interaction between salinity and light intensity within each life history phase generated observed differences between juvenile growth rates. Low light was shown to trigger early onset of alteration of the holdfast growing pattern. In addition, adult tetrasporophytes showed, despite the conditions, a faster vegetative growth than female and male gametophytes. These differences between phases could have led to the complete dominance of tetrasporophyte fragments of fronds observed in G. chilensis farms. We hypothesize that Chilean fishers could have unknowingly selected for tetrasporophyte thalli during domestication of the species, thus enhancing the natural trend of tetrasporophytes dominance already present in estuarine natural populations of free-floating plants.
Differential gene expression in Pyropia columbina (Bangiales, Rhodophyta) under natural hydration and desiccation conditions
(2013) Contreras-Porcia, Loretto; Lopez-Cristoffanini, Camilo; Lovazzano, Carlos; Rosa Flores-Molina, Maria; Thomas, Daniela; Nunez, Alejandra; Fierro, Camila; Guajardo, Eduardo; Correa, Juan A.; Kube, Michael; Reinhardt, Richard
In rocky shores, desiccation is triggered by daily tide changes, and experimental evidence suggests that local distribution of algal species across the intertidal rocky zone is related to their capacity to tolerate desiccation. In this context, the permanence of Pyropia columbina in the high intertidal rocky zone is explained by its exceptional physiological tolerance to desiccation. This study explored the metabolic pathways involved in tolerance to desiccation in the Chilean P. columbina, by characterizing its transcriptome under contrasting conditions of hydration. We obtained 1,410 ESTs from two subtracted cDNA libraries in naturally hydrated and desiccated fronds. Results indicate that transcriptome from both libraries contain transcripts from diverse metabolic pathways related to tolerance. Among the transcripts differentially expressed, 15% appears involved in protein synthesis, processing and degradation, 14.4% are related to photosynthesis and chloroplast, 13.1% to respiration and mitochondrial function (NADH dehydrogenase and cytochrome c oxidase proteins), 10.6% to cell wall metabolism, and 7.5% are involved in antioxidant activity, chaperone and defense factors (catalase, thioredoxin, heat shock proteins, cytochrome P450). Both libraries highlight the presence of genes/ proteins never described before in algae. This information provides the first molecular work regarding desiccation tolerance in P. columbina, and helps, to some extent, explaining the classical patterns of ecological distribution described for algae across the intertidal zone.
Diversity, phenomenology and epidemiology of epiphytism in farmed Gracilaria chilensis (Rhodophyta) in northern Chile
(2006) Leonardi, Patricia I.; Miravalles, Alicia B.; Faugeron, Sylvain; Flores, Veronica; Beltran, Jessica; Correa, Juan A.
This study identified the most common epiphytes infecting the algal host Gracilaria chilensis on a farm in northern Chile. Simultaneously, the types of host-epiphyte interfaces were characterized and their relative abundance and temporal variability were monitored. Five types of anatomical relationships were detected. Infection type I included the epiphytes weakly attached to the surface of the host and not associated with damage of host tissues (i.e. Hincksia mitchelliae, H. granulosa and Ectocarpus acutus). Infection type II included those epiphytes strongly attached to the surface of the host but not associated with any host tissue damage (i.e. Acrochaetium sp., Antithamnionella sp. and Colpomenia sinuosa). Infection type III included all the epiphytes that penetrated the outer layer of the host wall without damaging its cortical cells (i.e. Xenococcus sp. and Sahlingia subintegra). Infection type IV included epiphytes penetrating deep into the host cell wall, disorganizing the cortical tissue (i. e. Ulva lactuca and Acrosorium corallinarum). Infection type V included epiphytes that penetrated deeply into the cortex, reached the medullary tissue and caused destruction of the host's cells in the area around the infection (i.e. Ceramium rubrum and Polysiphonia harveyi). Prevalence varied with time and with infection type, with types II and III reaching up to 80% and 90% of the thalli respectively. Severity of epiphyte infection was similar to the distribution of infection prevalence, with crustose epiphytes colonizing up to 80% of the host surface.
Effects of copper on early developmental stages of Lessonia nigrescens Bory (Phaeophyceae)
(2007) Contreras, Loretto; Medina, Matias H.; Andrade, Santiago; Oppliger, Valeria; Correa, Juan A.
Copper effects on the early developmental gametophytic and sporophytic stages of the kelp Lessonia nigrescens were tested in gradients of increasing concentrations of ASV-Iabile copper. The results demonstrated a high sensitivity to copper of all life-history stages of the alga, where even the lowest tested concentration affected spore release as well as their subsequent settlement. More significant, concentrations higher than 7.87 mu g L-1 totally interrupted the development of the spores after they settle. This effect led to a failure in the formation of male and female ametophytes and, as a consequence, to a complete disruption of the normal life cycle of the kelp. Thus, we suggest that the absence of L. nigrescens from copper-enriched environments results from the high sensitivity of its early life cycle stages, which limits growth and maturation of the gametophytic microscopic phase and, as a consequence, prevents development of the macroscopic sporophytic phase. (c) 2006 Elsevier Ltd. All rights reserved.
Experimental transplants of the large kelp Lessonia nigrescens (Phaeophyceae) in high-energy wave exposed rocky intertidal habitats of northern Chile
(2006) Correa, Juan A.; Lagos, Nelson A.; Medina, Matias H.; Castilla, Juan C.; Cerda, Mauricio; Ramirez, Marco; Martinez, Enrique; Faugeron, Sylvain; Andrade, Santiago; Pinto, Raquel; Contreras, Loretto
Potential for addressing ecological and physiological issues becomes severely limited when the organisms required to experimentally test specific hypotheses are absent from the study areas. This report describes a simple and inexpensive device for re-planting kelps into the lower intertidal zone of wave-swept rocky habitats, using Lessonia nigrescens Bory as a model organism. The device allows a wide range of plant sizes to be anchored by the holdfast. Transplanted kelps regenerated, re-attached to the substratum and overgrew the transplanting device. These results confirm the feasibility of using this technique to tackle a variety of highly relevant questions involving ecological, physiological, conservation, restoration and management issues. (c) 2006 Elsevier B.V. All rights reserved.
Genetic diversity of Ectocarpus (Ectocarpales, Phaeophyceae) in Peru and northern Chile, the area of origin of the genome-sequenced strain
(2010) Peters, Akira F.; Mann, Aaron D.; Cordova, Cesar A.; Brodie, Juliet; Correa, Juan A.; Schroeder, Declan C.; Cock, J. Mark
P>The origin of the Ectocarpus strain used for genome sequencing (the 'genome strain') was Peru, where no Ectocarpus had been reported previously. To study the genetic diversity in the region and to increase the number of individuals from this area available for genetic experiments, 119 new Ectocarpus strains were isolated from eight localities along the 3000 km of coastline from central Peru to central Chile.
Herbivore-induced chemical and molecular responses of the kelps Laminaria digitata and Lessonia spicata
(2017) Ritter, Andres; Cabioch, Lea; Brillet-Gueguen, Loraine; Corre, Erwan; Cosse, Audrey; Dartevelle, Laurence; Durufle, Harold; Fasshauer, Carina; Goulitquer, Sophie; Thomas, Francois; Correa, Juan A.; Potin, Philippe; Faugeron, Sylvain; Leblanc, Catherine
Kelps are founding species of temperate marine ecosystems, living in intertidal coastal areas where they are often challenged by generalist and specialist herbivores. As most sessile organisms, kelps develop defensive strategies to restrain grazing damage and preserve their own fitness during interactions with herbivores. To decipher some inducible defense and signaling mechanisms, we carried out metabolome and transcriptome analyses in two emblematic kelp species, Lessonia spicata from South Pacific coasts and Laminaria digitata from North Atlantic, when challenged with their main specialist herbivores. Mass spectrometry based metabolomics revealed large metabolic changes induced in these two brown algae following challenges with their own specialist herbivores. Targeted metabolic profiling of L. spicata further showed that free fatty acid (FFA) and amino acid (AA) metabolisms were particularly regulated under grazing. An early stress response was illustrated by the accumulation of Sulphur containing amino acids in the first twelve hours of herbivory pressure. At latter time periods (after 24 hours), we observed FFA liberation and eicosanoid oxylipins synthesis likely representing metabolites related to stress. Global transcriptomic analysis identified sets of candidate genes specifically induced by grazing in both kelps. qPCR analysis of the top candidate genes during a 48-hours time course validated the results. Most of these genes were particularly activated by herbivore challenge after 24 hours, suggesting that transcriptional reprogramming could be operated at this time period. We demonstrated the potential utility of these genes as molecular markers for herbivory by measuring their inductions in grazed individuals of field harvested L. digitata and L. spicata. By unravelling the regulation of some metabolites and genes following grazing pressure in two kelps representative of the two hemispheres, this work contributes to provide a set of herbivore-induced chemical and molecular responses in kelp species, showing similar inducible responses upon specialist herbivores in their respective ecosystems.
IDENTIFICATION OF CRYPTIC SPECIES IN THE LESSONIA NIGRESCENS COMPLEX (PHAEOPHYCEAE, LAMINARIALES)
(WILEY, 2012) Gonzalez, Alejandra; Beltran, Jessica; Hiriart Bertrand, Luciano; Flores, Veronica; de Reviers, Bruno; Correa, Juan A.; Santelices, Bernabe
The kelp Lessonia nigrescens Bory is the most ecologically and economically important seaweed in rocky intertidal and shallow subtidal habitats along the temperate Pacific South American coasts. Recent molecular studies suggest the existence of two lineages, one (northern lineage) from 17 degrees S to 30 degrees S and a second (central lineage) from 29 degrees S to 41 degrees S. To identify and name these lineages we performed morphological, nomenclatural and field studies. Four external and three internal anatomical traits permitted a morphological separation of the two lineages. The internal structure of both lineages was different from the isolectotype of Lessonia nigrescens. It is therefore concluded that the name Lessonia nigrescens should not be used for the Chilean material. Chordaria spicata Suhr appears as the oldest available name for the central lineage, while Lessonia berteroana Montagne is the oldest name for the northern lineage. In both cases, the type material consisted of small-sized, apical branches of larger plants. The new combination Lessonia spicata (Suhr) Santelices is proposed for the central lineage and we reinstate Lessonia berteroana for the northern lineage. Laminaria scissa Suhr is reduced to synonym of L. spicata. Representative specimens of Lessonia nigrescens were not found during new visits to its type locality in Cape Horn and along Chile. Future studies should verify the status of this species.
Intraspecific biogeographic pattern breakage in the snapping shrimp Betaeus emarginatus caused by coastal copper mine tailings
(2008) Lardies, Marco A.; Medina, Matias H.; Correa, Juan A.
Environmental gradients are common in nature, and geographically widespread species must cope with environmental differences between habitats. Environmental differences produce bio-geographic patterns that can involve morphological, physiological, and life-history traits. The Bergmann's rule has been described as one of these ecological and evolutionary patterns, predicting an increase in body size towards colder climates. Human-induced polluting events could impair the performance and/or fitness of exposed individuals and populations. Thus, we hypothesized that species undergoing exposure to pollutants will show a breakage of the natural biogeographical variation of their fitness-related life-history traits. In northern Chile, copper mine tailings have been dumped continuously for more than 60 yr. Because the snapping shrimp Betaeus emarginatus is commonly found in intertidal pools near this dumping site, it was used as a study model. This shrimp has a pelagic larva and a wide distribution along the Chilean coast. Different life-history traits were studied in 5 populations over a range of 19 degrees of latitude along the Chilean coast. Population mean values for female body mass, egg volume, and reproductive output were positively correlated with latitude. In contrast, egg number was negatively correlated with latitude and positively correlated with temperature. Shrimps from the dumping site showed life-history trait values significantly lower than the range observed in areas with no copper enrichment, breaking the biogeographical patterns predicted by the Bergmann's rule. Such studies emphasize the need for integrating different concepts of organism and population ecology and life-history theory in the assessment of anthropogenic pollution.
Kinetics of copper accumulation in Lessonia nigrescens (Phaeophyceae) under conditions of environmental oxidative stress
(2006) Andrade, Santiago; Contreras, Loretto; Moffett, James W.; Correa, Juan A.
Juvenile individuals of the brown kelp Lessonia nigrescens were exposed to a coastal environment chronically impacted by copper mine wastes and currently displaying more than 250 nM of total dissolved copper. The kinetic of copper accumulation in the intra and extracellular compartments was determined and correlated to the oxidative burst resulting from copper-mediated oxidative stress. Accumulation involved an initial adsorption onto the outer cell wall followed by a slower uptake into the cells. A linear pattern of copper uptake over time was found during the first 52 h of exposure, and a steady state was reached at 76 h. The resulting oxidative stress was found to be inefficiently attenuated, and the intracellular level of copper remained sufficiently high to determine a persistently higher than normal level of reactive oxygen species (ROS). Thus, our results strongly suggest that, in L. nigrescens, copper needs to reach an intracellular threshold before oxidative burst develops. Furthermore, it was found that the high ROS levels generated by copper accumulation within the cells persists after the oxidative burst has ceased, suggesting a limited capacity of the algal tissue to buffer the increases of ROS caused by the environmental copper levels. (c) 2006 Elsevier B.V. All rights reserved.
LUIGI PROVASOLI AWARD RECIPIENTS
(2009) Thomas, Daniela; Beltran, Jessica; Flores, Veronica; Contreras, Loretto; Bollmann, Edda; Correa, Juan A.
As part of a long-term study on the biology and ecology of the intertidal kelp Lessonia nigrescens Bory, we report on the occurrence of gall development on this alga, identified the possible causal agent, and assessed the extent of the phenomenon in two wild stands of the host. Our results showed that galls affecting natural populations of L. nigrescens were associated with the infection by a filamentous brown algal endophyte of the genus Laminariocolax. Assignment to Laminariocolax of the endophytes isolated from cultured gall tissue was based on the (i)high internal transcribed spacer 1 (ITS1) sequence similarity and phylogenetic relationship between the Chilean isolates and several species of the genus Laminariocolax endophytic in other kelps, (ii) reproductive and vegetative features of the endophyte in culture, and (iii) anatomical agreement of fully developed galls of Lessonia with those described for other kelp galls caused by endophytic members of Laminariocolax. Unequivocal identification at the species level of the endophytes infecting Lessonia, however, awaits further studies.
Parthenogenesis in the brown alga Lessonia nigrescens (Laminariales, Phaeophyceae) from central Chile
(2007) Oppliger, L. Valeria; Correa, Juan A.; Peters, Akira F.
Parthenogenesis, the development of female gametes without fertilization, is relatively common in brown algae, although limited quantitative information on the phenomenon is available. Its occurrence is reported for the first time in Lessonia nigrescens Bory, a member of the Laminariales and a key ecological component of the benthic algal communities along the Chilean coast. Isolated female gametophytes developed into parthenosporophytes throughout the year, with a maximum in spring to early summer. Isolated male gametophytes, on the other hand, never developed fronds. Parthenosporophytes obtained in the laboratory developed normally when cultivated under greenhouse conditions, and the resulting individuals were indistinguishable in size, shape, texture, and color from heterozygous sporophytes. Quantification of DNA of various tissues demonstrated that early during their development, parthenosporophytes duplicated their DNA content, displaying levels similar to heterozygous sporophytes and almost twice the level found in gametophytes. One out of 45 individuals from a field population yielded only female gametophytes, strongly suggesting that parthenogenesis does occur in wild stands of L. nigrescens.
Phylogeographic analyses of the 30°S south-east Pacific biogeographic transition zone establish the occurrence of a sharp genetic discontinuity in the kelp Lessonia nigrescens: Vicariance or parapatry?
(2009) Tellier, Florence; Meynard, Andres P.; Correa, Juan A.; Faugeron, Sylvain; Valero, Myriam
Phylogeographic studies are lacking in the Southern Hemisphere, and in particular in the south-eastern Pacific. To infer the possible scenario for the debated biogeographic transition zone located at 30-33 degrees S along the Chilean coast, we investigated whether there is a concordance between the phylogeographic pattern and the biogeographic transition in the intertidal kelp Lessonia nigrescens; whose distribution is continuous across this transition zone. Using a combination of four makers located in the three genomic compartments (chloroplast, mitochondria and nucleus), we showed the presence of two main divergent lineages, possibly cryptic species. There was an exact match of the phylogeographic break with the 30 degrees S biogeographic transition zone, suggesting a common origin. The combined information given by the multilocus approach and by the population analysis suggested the occurrence of a budding speciation, with a northward range expansion. (C) 2009 Elsevier Inc. All rights reserved.
Proteomic analysis and identification of copper stress-regulated proteins in the marine alga Scytosiphon gracilis (Phaeophyceae)
(2010) Contreras, Loretto; Moenne, Alejandra; Gaillard, Fanny; Potin, Philippe; Correa, Juan A.
A proteomic analysis combining peptide de novo sequencing and BLAST analysis was used to identify novel proteins involved in copper tolerance in the marine alga Scytosiphon gracilis (Phaeophyceae). Algal material was cultivated in seawater without copper (control) or supplemented with 100 mu g L(-1) for 4 days, and protein extracts were separated by two-dimensional gel electrophoresis (2-DE). From the proteins obtained in the copper treatment, 25 over-expressed, 5 under-expressed and 5 proteins with no changes as compared with the control, were selected for sequencing. Tryptic-peptides obtained from 35 spots were analyzed by capillary liquid chromatography and tandem mass spectroscopy (capLC/MS/MS). and protein identity was determined by BLASTP. We identified 19 over-expressed proteins, including a chloroplast peroxiredoxin, a cytosolic phosphomannomutase, a cytosolic glyceraldehyde-3-phosphate dehydrogenase, 3 ABC transporters, a chaperonine, a subunit of the proteasome and a tRNA synthase, among others. The possible involvement of these over-expressed proteins in buffering oxidative stress and avoiding metal uptake in S. gracilis exposed to copper excess is discussed taking into consideration the information available for other plant models. (C) 2009 Elsevier B.V. All rights reserved.
Seaweeds early development: detrimental effects of desiccation and attenuation by algal extracts
(2012) Contreras-Porcia, Loretto; Callejas, Sebastian; Thomas, Daniela; Sordet, Camille; Pohnert, Georg; Contreras, Anibal; Lafuente, Ana; Flores-Molina, Maria R.; Correa, Juan A.
The effects of desiccation on the early development stages of Mazzaella laminarioides, Scytosiphon lomentaria and Lessonia nigrescens, algal species with different patterns of distribution across the intertidal zone, were examined in the laboratory. In addition, the protective effect against desiccation was evaluated using algal extracts, including those from Porphyra columbina, a macroalga tolerant to desiccation that lives in the uppermost part of the intertidal zone. Our results showed that M. laminarioides displayed the highest resistance to daily desiccation, followed by S. lomentaria, whereas L. nigrescens was the most susceptible. Spores from L. nigrescens exposed to desiccation, although being able to germinate, ceased further post-germination development. In addition, our results showed that all species exposed to extracts from desiccated P. columbina successfully completed their development and strongly suggest the occurrence of compounds with protective properties that help in attenuating the stress caused by desiccation. Finally, our results indicate that the magnitude of the effects generated by desiccation on the early algal development is related to the position of the species in the intertidal zone, and that the protective effects of P. columbina extracts reveal an exceptional metabolism of this species under desiccation stress.
SEX RATIO VARIATION IN THE LESSONIA NIGRESCENS COMPLEX (LAMINARIALES, PHAEOPHYCEAE): EFFECT OF LATITUDE, TEMPERATURE, AND MARGINALITY
(WILEY, 2011) Oppliger, Luz Valeria; Correa, Juan A.; Faugeron, Sylvain; Beltran, Jessica; Tellier, Florence; Valero, Myriam; Destombe, Christophe
Little is known about variation of sex ratio, the proportion of males to females, in natural populations of seaweed, though it is a major determinant of the mating system. The observation of sexual chromosomes in kelps suggested that sex is partly genetically determined. However, it is probably not purely genetic since the sex ratio can be modified by environmental factors such as salinity or temperature. In this paper, sex ratio variation was studied in the kelp Lessonia nigrescens Bory complex, recently identified as two cryptic species occurring along the Chilean coast: one located north and the other south of the biogeographic boundary at latitude 29 degrees-30 degrees S. The life cycle of L. nigrescens is characterized by an alternation of microscopic haploid gametophytic individuals and large macroscopic fronds of diploid sporophytes. The sex ratio was recorded in progenies from 241 sporophytic individuals collected from 13 populations distributed along the Chilean coast in order (i) to examine the effect of an environmental gradient coupled with latitude, and (ii) to compare marginal populations to central populations of the two species. In addition, we tested the hypothesis that the sex ratios of the two cryptic species would be affected differently by temperature. First, our results demonstrate that sex ratio seems to be mainly genetically determined and temperature can significantly modify it. Populations of the northern species showed a lower frequency of males at 14 degrees C than at 10 degrees C, whereas populations of the southern species showed the opposite pattern. Second, both species displayed an increased variation in sex ratio at the range limits. This greater variation at the margins could be due either to differential mortality between sexes or to geographic parthenogenesis (asexual reproduction).
Spatial and temporal variation of photosynthesis in intertidal Mazzaella laminarioides (Bory)Fredericq (Rhodophyta, Gigartinales)
(2006) Varela, Daniel A.; Santelices, Bernabe; Correa, Juan A.; Arroyo, Mary K.
The red alga Mazzaella laminarioides is an economically important species with an extended latitudinal distribution along the Chilean coast. Its populations form mid-intertidal stands, several meters wide, and therefore are differentially exposed to environmental variables that result in temporal and spatial variability in productivity. We evaluated the effect of latitude and intertidal height on productivity by in situ measurement of photosynthetic performance. Daily and seasonal variations of O-2-evolution rate and maximal quantum yield (F (v)/F (m)) were determined in plants from the upper and lower intertidal zone at two localities 1500,km apart. Results suggest that plant responses were mainly affected by irradiation, temperature and desiccation. At local level, upper intertidal plants showed a reduced photosynthetic rate and quantum efficiency as compared to those displayed by plants from the lower intertidal, indicating their higher level of excitation energy acclimation. Stronger acclimation differences between upper and lower intertidal plants were observed in spring and summer. Differences in photosynthetic parameters between reproductive phases were recorded in autumn and winter, regardless of the position of the individuals in the intertidal zone. The effects of tidal elevation on seasonal patterns of photosynthesis were also influenced by latitude. Seasonal variation in photosynthetic efficiency was observed in plants from the northern population at both intertidal elevations, but only at the upper intertidal level in the southern population. This study shows that production variability in M. laminarioides results from differences in the intensity of environmental factors observed seasonally at local (intertidal) and latitudinal scales.
Spore release in Acrochaetium sp (Rhodophyta) is bacterially controlled
(2007) Weinberger, Florian; Beltran, Jessica; Correa, Juan A.; Lion, Ulrich; Pohnert, Georg; Kumar, Naresh; Steinberg, Peter; Kloareg, Bernard; Potin, Philippe
The facultative red algal epiphyte Acrochaetium sp. liberated spores preferentially and recruited more successfully in laboratory cultures when its host Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira was present. The same effect was also induced by cell-free medium from G. chilensis, suggesting it contained a molecular signal. Antibiotics prevented spore release in Acrochaetium sp., even when G. chilensis was present, suggesting a prokaryotic origin of the signal. Simultaneous application of N-butyl-homoserine-lactone (BHL) restored the spore-release capacity, which demonstrated that spore release was not directly inhibited by the antibiotics and indicated that bacterially generated N-acyl-homoserine-lactones (AHLs) regulate spore release. An involvement of AHL was further indicated by the fact that two different halofuranone inhibitors of AHL receptors also inhibited spore release when they were applied at relatively low concentrations. Of seven different AHLs tested, only BHL induced the effect. However, BHL was only active at relatively high concentrations (100 mu M), and it was not detected in spore-release-inducing medium of G. chilensis. Another water-soluble AHL or an AHL structure analog is therefore probably the active compound in G. chilensis cultures. The data presented demonstrate that life cycle completion in Acrochaetium sp. strongly depends on bacteria, which are not always present in sufficient numbers on the alga itself. Exogenous bacteria that are associated with G. chilensis or with other potential substrates may therefore trigger timely spore liberation in Acrochaetium sp., provided that the necessary concentration of AHL is reached. This first finding of AHL perception in a red alga confirms that AHL signalling is more widespread among eukaryotes than was thought until recently. However, spore release of a second red alga, Sahlingia subintegra (Rosenv.) Kornmann, was unaffected by AHL, and the reaction observed is therefore not universal.

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