Multixenobiotic defense mechanism (MDMX) in bivalves

Multixenobiotic defence mechanism (MXDM) consists in a cellular system that functions as membrane extrusion pumps effluxing organic compounds out of the cells. In bivalves, it represents a primordial protection against toxic effects of organic xenobiotics in preventing their cellular accumulation. It has raised attention during the last decade for its potential to be used as a biomarker of pollution. This article reviews the fundamental knowledge on the MXDM system in bivalves and the methods proposed to assess its activity. Finally, it reviews the major results of laboratory and field studies that enabled to hypothesise that MXDM could be used as a biomarker of environmental stress rather than of pollutant exposure.     

Anoxic survival of Macoma balthica: the effect of antibiotics, molybdate and sulphide

In anoxic semi-closed systems, the survival time of the clam Macoma balthica was compared to clams which were incubated in the presence of several antibiotics (chloramphenicol, 5-oxytetracycline hydrochloride, penicillin, streptomycin, a mix of penicillin and streptomycin and a mix of chloramphenicol, polymyxin, neomycin and penicillin), sulphide and chloramphenicol at pH 6.8 and 8.2 and molybdate (specific inhibitor of the process of sulphate reduction). The aim was to detect maximum survival times of this clam and indications for the cause of mortality under the conditions tested. Median survival time (LT(50)) of the clam was 4.8 days (at 19 degrees C) in incubations without any addition. Added sulphide (200 μM) decreased survival time. At pH 8.2, LT(50) decreased by 20.8% and at pH 6.8 by 35.2%. However, added molybdate, which suppressed biotic sulphide formation, did not improve survival time (LT(50)=4.4 days). Biotic sulphide probably did not speed up mortality rate, but indicated excessive growth of sulphate reducing bacteria once mortality started. The presence of different antibiotics increased significantly survival time (LT(50)) from 8.9 to 14.9 days. Qualitative estimations were made of the numbers of bacteria present in the systems. Compared to a seawater control, highest numbers were observed in the incubation of clams without additions and in the presence of molybdate. Nevertheless, due to the presence of molybdate, bacteria numbers were significantly lower. However, very low numbers of bacteria were observed in the incubations of clams in the presence of chloramphenicol. These data demonstrated that the presence and proliferation of bacteria was probably the cause of death of the clams.     

Local scale DNA barcoding of bivalves (Mollusca): a case study

Divergence in cytochrome c oxidase 1 (COI), the genetic marker proposed for DNA barcoding, was investigated in marine bivalves from the genera Ennucula , Nucula , Yoldiella and Thyasira . No overlap in levels of intra- and interspecific variation was found. The levels of divergence found suggest that barcodes from COI will be useful in distinguishing between the species investigated in this study. The insufficiency of blast searches in GenBank to assign many of the obtained sequences to correct phylum was noted and clearly demonstrates the need for better search strategies specifically targeted at identification using DNA barcodes.     

The pathogenic potential of endogenous retroviruses: facts and fantasies.

Endogenous retroviruses are descendants of viruses that became cellular genes by integration into their host's genome. They still contribute to pathogenicity as a partner in recombination events, by de novo insertion after mobilization followed by activation of downstream proto-oncogenes, or by gene disruption. Re-expression of viral proteins accompanied by loss of immune tolerance could induce immune disturbances.     

Sustainability and cyanobacteria (blue-green algae): facts and challenges

Cyanobacteria (blue-green algae) are widely distributed Gram-negative oxygenic photosynthetic prokaryotes with a long evolutionary history. They have potential applications such as nutrition (food supplements and fine chemicals), in agriculture (as biofertilizer and in reclamation of saline USAR soils) and in wastewater treatment (production of exopolysaccharides and flocculants). In addition, they also produce wide variety of chemicals not needed for their normal growth (secondary metabolites) which show powerful biological activities such as strong antiviral, antibacterial, antifungal, antimalarial, antitumoral and anti-inflammatory activities useful for therapeutic purposes. In recent years, cyanobacteria have gained interest for producing biofuels (both biomass and H₂ production). Because of their simple growth needs, it is potentially cost-effective to exploit cyanobacteria for the production of recombinant compounds of medicinal and commercial value. Recent advances in culture, screening and genetic engineering techniques have opened new ways to exploit the potential of cyanobacteria. This review analyses the sustainability of cyanobacteria to solve global problems such as food, energy and environmental degradation. It emphasizes the need to adopt multidisciplinary approaches and a multi-product production (biorefinery) strategy to harness the maximum benefit of cyanobacteria.     

Anoxic survival of the isolated cerebellum of the turtle Pseudemis scripta elegans

Intact turtle brain provides a useful model for the study of anoxia and potential survival strategies, since this tissue maintains transmembrane ion gradients and ATP levels during prolonged anoxia and recovers functional activity afterwards. Since isolated tissues offer experimental advantages, the present study sought to determine effects of anoxia on the isolated turtle cerebellum and to define relationships between anoxia survival and glucose supply. In normoxia, the extracellular potassium ([K+]o) activity and evoked potentials were maintained with 5 mM glucose, but 20 mM glucose was required to maintain adenosine triphosphate (ATP) levels and prevent significant increases in [K+]o during anoxia. Inhibition of glycolysis by iodoacetic acid (IAA) during anoxia provoked large increases in [K+]o at all glucose levels. These results demonstrate the usefulness of the isolated turtle cerebellum for studies of anoxic survival since this tissue can maintain ATP levels and [K+]o during prolonged anoxia with 20 mM glucose in the artificial cerebrospinal fluid medium. They also suggest the presence of a Pasteur effect at least during the transition to a hypometabolic state.     

The microsculpture of glochidia of some anodontine bivalves (Unionidae)

Glochidia of three freshwater anodontine bivalves: Kunashiria Starobogatov in Zatrawkin, 1983, Sinanodonta Modell, 1944, from the Far East, and Anodonta Lamarck, 1799, were investigated by scanning electron microscopy. Data on the microsculpture of the outer surface of glochidial valves are given. Among the three genera discussed, the glochidia of Anodonta are the largest, with a loose-looped outer microsculpture and numerous granules. The glochidia of Kunashiria and Sinanodonta differ by the valve height–length proportions and some details of the outer microsculpture: glochidia of Kunashiria have a tight-looped outer sculpture while the glochidia of Sinanodonta have a loose-net outer sculpture.     

Evolution of ancient lake bivalves: the Lymnocardiinae (Cardiidae) of the Caspian Sea

The Caspian Sea as the largest continental water body in the world is known for its comparably high levels of biodiversity and endemism, also in mollusks. The evolution of a euryhaline taxon of cardiid bivalves, the Lymnocardiinae of the Ponto-Caspian region, remains unclear today. We studied material from the whole recent range of Lymnocardiinae (i.e., the Caspian, the Azov, and the Black Seas) using a LSU rDNA phylogeny aiming at (a) testing the monophyly of Lymnocardiinae and (b) determining the phylogenetic relationships within Cardiidae. Lymnocardiinae s.str. were monophyletic, i.e., a distinct group that included species of Hypanis, Didacna, and Monodacna. Lymnocardiinae as often understood, i.e., including Cerastoderma, are not monophyletic in our analysis and Cerastoderma should thus be transferred to Cardiinae. The Lymnocardiinae s.str. had a shallow tree topology and were poorly resolved. No clearcut biogeographical pattern could be derived from the phylogeny, i.e., species stemming from respective Ponto-Caspian regions, do not necessarily cluster together. We discuss a scenario of the evolutionary history and biogeographical (as well as taxonomic) implications. Given the complex history of the Ponto-Caspian region and the Caspian Sea in particular, the Lymnocardiinae would represent an interesting study object for addressing the consequences of environmental changes on biotic evolution at various spatial and temporal scales.     

Aneuploidy in man (facts and hypotheses)

Mechanisms of the human aneuploidy formation are discussed proceeding from the review of the published data obtained by Soviet and foreign authors. It is supposed that hereditary determination of this process plays a main role as compared with new genomic mutations resulting from the induction by ecological factors. Microstructural rearrangements and nonhomologous recombination in nondisjunction of chromosomes during cell division are considered parallel with mosaicism as one of possible reasons of genetic predisposition.     

Anoxic survival of the Pacific hagfish (<Emphasis Type="Italic">Eptatretus stoutii</Emphasis>)

It is not known how the Pacific hagfish (Eptatretus stoutii) can survive extended periods of anoxia. The present study used two experimental approaches to examine energy use during and following anoxic exposure periods of different durations (6, 24 and 36 h). By measuring oxygen consumption prior to anoxic exposure, we detected a circadian rhythm, with hagfish being active during night and showing a minimum routine oxygen consumption (RMR) during the daytime. By measuring the excess post-anoxic oxygen consumption (EPAOC) after 6 and 24 h it was possible to mathematically account for RMR being maintained even though heme stores of oxygen would have been depleted by the animal’s metabolism during the first hours of anoxia. However, EPAOC after 36 h of anoxia could not account for RMR being maintained. Measurements of tissue glycogen disappearance and lactate appearance during anoxia showed that the degree of glycolysis and the timing of its activation varied among tissues. Yet, neither measurement could account for the RMR being maintained during even the 6-h anoxic period. Therefore, two independent analyses of the metabolic responses of hagfish to anoxia exposure suggest that hagfish utilize metabolic rate suppression as part of the strategy for longer-term anoxia survival.     

Assisted reproductive technology (ART) in humans: facts and uncertainties

Since the first in vitro fertilization (IVF) in human, the number of patients using Assisted Reproductive Technologies (ART) has increased tremendously. ART technologies have increased in number and their spectrum has also widened. The first IVF babies are now more than 20 years old. All the retrospective analyses have demonstrated that the obstetrical and pediatrical impact has not really affected single births. The main problems observed occur with multiple pregnancies, including high costs for the couples and for society. The decrease in the number of embryos transferred has improved the situation and moreover does not impair the final results. IntraCytoplasmic Sperm Injection (ICSI) is a more debatable and questionable technique with a real negative genetic impact. The main problem is chromosome abnormalities more specifically related to the sex chromosomes. The question of a systematic genetic work-up on the patients entering ICSI programs is discussed. No negative impact of cryopreservation has been demonstrated even though some controversy arises from time to time. Pre-implantation Genetic Diagnosis (PGD) is now a interesting tool for patients carrying genetic defects. Blastocyst biopsy now has a future role in reproductive medicine. Gender selection through sperm sorting is also now a reality. As with the other developing bio-technologies related to reproduction, there are ethical questions. The decisions concerning these technologies do not belong solely to scientists but are rather a matter for society to decide.     

Bacterial Dissimilatory Reduction of Arsenic(V) to Arsenic(III) in Anoxic Sediments

Incubation of anoxic salt marsh sediment slurries with 10 mM As(V) resulted in the disappearance over time of the As(V) in conjunction with its recovery as As(III). No As(V) reduction to As(III) occurred in heat-sterilized or formalin-killed controls or in live sediments incubated in air. The rate of As(V) reduction in slurries was enhanced by addition of the electron donor lactate, H(inf2), or glucose, whereas the respiratory inhibitor/uncoupler dinitrophenol, rotenone, or 2-heptyl-4-hydroxyquinoline N-oxide blocked As(V) reduction. As(V) reduction was also inhibited by tungstate but not by molybdate, sulfate, or phosphate. Nitrate inhibited As(V) reduction by its action as a preferred respiratory electron acceptor rather than as a structural analog of As(V). Nitrate-respiring sediments could reduce As(V) to As(III) once all the nitrate was removed. Chloramphenicol blocked the reduction of As(V) to As(III) in nitrate-respiring sediments, suggesting that nitrate and arsenate were reduced by separate enzyme systems. Oxidation of [2-(sup14)C]acetate to (sup14)CO(inf2) by salt marsh and freshwater sediments was coupled to As(V). Collectively, these results show that reduction of As(V) in sediments proceeds by a dissimilatory process. Bacterial sulfate reduction was completely inhibited by As(V) as well as by As(III).     

Fouling of European freshwater bivalves (Unionidae) by the invasive zebra mussel (Dreissena polymorpha)

1. The zebra mussel (Dreissena polymorpha) is well known for its invasive success and its ecological and economic impacts. Of particular concern has been the regional extinction of North American freshwater mussels (Order Unionoida) on whose exposed shells the zebra mussels settle. Surprisingly, relatively little attention has been given to the fouling of European unionoids. 2. We investigated interspecific patterns in fouling at six United Kingdom localities between 1998 and 2008. To quantify the effect on two pan‐European unionoids (Anodonta anatina and Unio pictorum), we used two measures of physiological status: tissue mass : shell mass and tissue glycogen content. 3. The proportion of fouled mussels increased between 1998 and 2008, reflecting the recent, rapid increase in zebra mussels in the U.K. Anodonta anatina was consistently more heavily fouled than U. pictorum and had a greater surface area of shell exposed in the water column. 4. Fouled mussels had a lower physiological condition than unfouled mussels. Unlike tissue mass : shell mass ratio, tissue glycogen content was independent of mussel size, making it a particularly useful measure of condition. Unio pictorum showed a stronger decline in glycogen with increasing zebra mussel load, but had a broadly higher condition than A. anatina at the time of study (July). 5. Given the high conservation status and important ecological roles of unionoids, the increased spatial distribution and fouling rates by D. polymorpha in Europe should receive more attention.     

Experimental deep-sea deployments reveal diverse Northeast Pacific wood-boring bivalves of Xylophagainae (Myoida: Pholadidae)

Only a single species of deep-sea wood boring bivalve has beenknown off the forested northwest coast of North America, althoughthe Xylophagainae are so diverse in other areas that up to fivespecies occur in a given length of wood. To determine whetheradditional species were present in the Northeast Pacific andif so, how they coexist, lengths of wood were experimentallydeployed on heavily sedimented sites on the Cascadia Basin andEscanaba Trough, non-hydrothermally active basalt on Gorda Ridgeand Axial Volcano, and an isolated sediment pond within theaxis of Juan de Fuca Ridge, at depths of between 1,530 and 3,232 m.All locations were between 41°and 48°N, at least 240 kmoff the North American coast. Six previously unknown species,Xylophaga corona n. sp., X. zierenbergi n. sp., X. heterosiphonn. sp., X. oregona n. sp., X. microchira n. sp. and Xylopholascrooki n. sp., were collected and are described here. Dominantspecies differed in recoveries made after 10 and 24 months atJuan de Fuca Ridge and Cascadia Basin localities. Xylophagamicrochira n. sp. dominated four of five deployments recoveredwithin 12 months, but its abundance declined by 24 months, beinglargely replaced on Juan de Fuca Ridge by X. oregona n. sp.,a species known only from this Ridge and from an incidentalcollection on the Nootka Fracture Zone. At Cascadia Basin sites,the abundances of X. heterosiphon n. sp. and of what are likelyto be predatory polyclad flatworms increased as that of X. microchiran. sp. declined. Xylophaga microchira n. sp. is hypothesizedto be specialized for early colonization, but to be competitivelyinferior to X. oregona n. sp., and more vulnerable to predatorsthan X. heterosiphon n. sp. The dominance of competitively superiorand more predator-resistant species in older deployments arguesthat biotic interactions contribute to coexistence of multiplespecies of wood-borers despite direct competition among them. (Received 2 February 2007; accepted 16 August 2007)     

Vertical Distribution of Methanogens in the Anoxic Sediment of Rotsee (Switzerland)

Anoxic sediments from Rotsee (Switzerland) were analyzed for the presence and diversity of methanogens by using molecular tools and for methanogenic activity by using radiotracer techniques, in addition to the measurement of chemical profiles. After PCR-assisted sequence retrieval of the 16S rRNA genes (16S rDNA) from the anoxic sediment of Rotsee, cloning, and sequencing, a phylogenetic analysis identified two clusters of sequences and four separated clones. The sequences in cluster 1 grouped with those of Methanosaeta spp., whereas the sequences in cluster 2 comprised the methanogenic endosymbiont of Plagiopyla nasuta. Discriminative oligonucleotide probes were constructed against both clusters and two of the separated clones. These probes were used subsequently for the analysis of indigenous methanogens in a core of the sediment, in addition to domain-specific probes against members of the domains Bacteria and Archaea and the fluorescent stain 4′,6-diamidino-2-phenylindole (DAPI), by fluorescent in situ hybridization. After DAPI staining, the highest microbial density was obtained in the upper sediment layer; this density decreased with depth from (1.01 ± 0.25) × 10¹⁰ to (2.62 ± 0.58) × 10¹⁰ cells per g of sediment (dry weight). This zone corresponded to that of highest metabolic activity, as indicated by the ammonia, alkalinity, and pH profiles, whereas the methane profile was constant. Probes Eub338 and Arch915 detected on average 16 and 6% of the DAPI-stained cells as members of the domains Bacteria and Archaea, respectively. Probe Rotcl1 identified on average 4% of the DAPI-stained cells as Methanosaeta spp., which were present throughout the whole core. In contrast, probe Rotcl2 identified only 0.7% of the DAPI-stained cells as relatives of the methanogenic endosymbiont of P. nasuta, which was present exclusively in the upper 2 cm of the sediment. Probes Rotp13 and Rotp17 did not detect any cells. The spatial distribution of the two methanogenic populations corresponded well to the methane production rates determined by incubation with either [¹⁴C]acetate or [¹⁴C]bicarbonate. Methanogenesis from acetate accounted for almost all of the total methane production, which concurs with the predominance of acetoclastic Methanosaeta spp. that represented on average 91% of the archaeal population. Significant hydrogenotrophic methanogenesis was found only in the organically enriched upper 2 cm of the sediment, where the probably hydrogenotrophic relatives of the methanogenic endosymbiont of P. nasuta, accounting on average for 7% of the archaeal population, were also detected.     

Lipid radical generation in polar (Laternula elliptica) and temperate (Mya arenaria) bivalves

Lipid peroxidation in Laternula elliptica was assessed by detecting lipid radicals by electronic paramagnetic resonance. The values were compared with data from the temperate mud clam Mya arenaria. Lipid radical content was higher in the Antarctic bivalve than in the temperate mud clam, even within the range of its habitat temperature. The rate of generation of lipid radicals was affected by the iron content in the samples. The iron content in individual samples of digestive glands in L. elliptica ranged from 3 to 6 nmol g⁻¹ fresh weight (fwt) and in M. arenaria from 0.6 to 2.7 nmol g⁻¹ fwt. Arrhenius plots, developed from the rates obtained in the presence of 25 μM iron, showed no significant differences between the activation energy calculated for digestive glands of L. elliptica and M. arenaria. The Fe³⁺ reduction rate in L. elliptica was higher than in M. arenaria (4.7±0.9 vs. 1.8±0.4 nmol mg⁻¹ protein min⁻¹, respectively). L. elliptica had a higher content of α-tocopherol and β-carotene than M. arenaria. Our data suggest that increased lipid radical content in the membranes of cold-adapted organisms could be related to iron content.     

Novel Eukaryotes from the Permanently Anoxic Cariaco Basin (Caribbean Sea)

Present knowledge of microbial diversity is decidedly incomplete (S. J. Giovannoni and M. S. Rappé, p. 47-84, in D. Kirchman, ed., Microbial Ecology of the Oceans, 2000; E. Stackebrandt and T. M. Embley, p. 57-75, in R. R. Colwell and D. J. Grimes, ed., Nonculturable Microorganisms in the Environment, 2000). Protistan phylogenies are particularly deficient and undoubtedly exclude clades of principal ecological and evolutionary importance (S. L. Baldauf, Science 300:1703-1706, 2003). The rRNA approach has been extraordinarily successful in expanding the global prokaryotic record (S. J. Giovannoni and M. S. Rappé, p. 47-84, in D. Kirchman, ed., Microbial Ecology of the Oceans, 2000; E. Stackebrandt and T. M. Embley, p. 57-75, in R. R. Colwell and D. J. Grimes, ed., Nonculturable Microorganisms in the Environment, 2000) but has rarely been used in protistan discovery. Here we report the first application of the 18S rRNA approach to a permanently anoxic environment, the Cariaco Basin off the Venezuelan coast. On the basis of rRNA sequences, we uncovered a substantial number of novel protistan lineages. These included new clades of the highest taxonomic level unrelated to any known eukaryote as well as deep branches within established protistan groups. Three novel lineages branch at the base of the eukaryotic evolutionary tree preceding, contemporary with, or immediately following the earliest eukaryotic branches. These newly discovered protists may retain traits reminiscent of an early eukaryotic ancestor(s).     

Aquatic respiration as a potential survival mechanism of Brephidium pseudofea (Lepidoptera: Lycaenidae) larvae to intertidal environments

The eastern pygmy blue, Brephidium pseudofea (Morrison) (Lepidoptera: Lycaenidae: Polyommatinae), inhabits intertidal environments that are periodically flooded. The immature stages are subject to salt or brackish water inundation during this time and therefore must endure many stressors, including respiratory limitation and salt exposure. Our goal was to investigate possible mechanisms used by the larval stages of B. pseudofea to endure periodic tidal inundation by using physiological and morphological analyses in comparison with several species of terrestrial lepidopteran larvae. A review of tidal charts showed that the immature stages of B. pseudofea would be prone to complete inundation two to five times per month during the summer months (May to August) and partial submersion for up to 20 d per month during the rest of the year. Larvae of several terrestrial lepidopteran species studied consumed oxygen under water for a limited period, but B. pseudofea demonstrated substantially higher oxygen consumption. Light microscopy of B. pseudofea larvae revealed small air pockets in and around the spiracles when submerged in tap water; these air pockets disappeared when exposed to detergent solution. The resulting air pockets may function as a diffusion layer for oxygen to be absorbed from the surrounding water or may act in conjunction with trans-cuticular gas exchange to meet the larva's respiratory needs. Morphological examination by scanning electron microscopy showed that B. psudofea larvae have distinctively small, clavate setae that appear insufficient to effectively support a functional plastron.     

Epstein-Barr virus (EBV) and human disease: facts, opinions and problems

The human herpesvirus, Epstein-Barr virus (EBV), has classically been associated with two pathologies with frequencies approaching 100%. One of these, Burkitt's lymphoma (BL), is of B-cell origin and the other, nasopharyngeal carcinoma (NPC), is a tumour of poorly differentiated epithelial cells. More recently, EBV had been identified with frequencies from a few percent to 100% (in one case) with a variety of other malignancies. These include Hodgkin's disease (HD; where in the west, the frequency of association is about 50%), sino-nasal T-cell lymphomas, lymphoepitheliomas, some sarcomas and breast cancers, other cancers from the head and neck, and lymphomas arising in patients with immune dysfunctions. Since EBV is ubiquitous, with the vast majority of the world's population having met and seroconverted to the virus, the diversity of tumours with which it has now been associated represents a substantial health burden. In a recent IARC monograph, EBV was classified as a group 1 carcinogen. Here, the data on BL and NPC, as they relate to geographical restrictions, viral strain variation, co-factors in disease, and genetic components are reexamined. We raise the question whether in their origins, these tumours genuinely reflect distinct and independent events, as deemed at present, or may represent a response by different cell types to common extracellular factors. For example, a situation in Kenya apparently existed in the past, where both BL and NPC were observed in ethnic Africans with roughly equal frequencies; more recently, in Kenya, EBV has been identified in nearly 100% of the tumours in children with HD. We also consider tumours where the viral association is reportedly of low frequency, and offer explanations for these data, including the possibility of loss of the viral genome once malignancy has been initiated. If this phenomenon occurs as a frequent secondary event, EBV could be an even greater health risk than presently believed.