Role of AIP56 disulphide bond and its reduction by cytosolic redox systems for efficient intoxication

Apoptosis‐inducing protein of 56 kDa (AIP56) is a major virulence factor of Photobacterium damselae subsp. piscicida, a gram‐negative pathogen that infects warm water fish species worldwide and causes serious economic losses in aquacultures. AIP56 is a single‐chain AB toxin composed by two domains connected by an unstructured linker peptide flanked by two cysteine residues that form a disulphide bond. The A domain comprises a zinc‐metalloprotease moiety that cleaves the NF‐kB p65, and the B domain is involved in binding and internalisation of the toxin into susceptible cells. Previous experiments suggested that disruption of AIP56 disulphide bond partially compromised toxicity, but conclusive evidences supporting the importance of that bond in intoxication were lacking. Here, we show that although the disulphide bond of AIP56 is dispensable for receptor recognition, endocytosis, and membrane interaction, it needs to be intact for efficient translocation of the toxin into the cytosol. We also show that the host cell thioredoxin reductase‐thioredoxin system is involved in AIP56 intoxication by reducing the disulphide bond of the toxin at the cytosol. The present study contributes to a better understanding of the molecular mechanisms operating during AIP56 intoxication and reveals common features shared with other AB toxins.     

Engineering Natural and Synthetic Resistance for Nematode Management

Bioengineering strategies are being developed that will provide specific and durable resistance against plant-parasitic nematodes in crops. The strategies come under three categories: (i) transfer of natural resistance genes from plants that have them to plants that do not, to mobilize the defense mechanisms in susceptible crops; (ii) interference with the biochemical signals that nematodes exchange with plants during parasitic interactions, especially those resulting in the formation of specialized feeding sites for the sedentary endoparasites—many nematode genes and many plant genes are potential targets for manipulation; and (iii) expression in plant cells of proteins toxic to nematodes.     

三种鹅膏菌培养条件及所产肽类毒素的比较研究

以外生菌根菌鹅膏菌属三个种Amanita muscaria,A.pseudoporphyria和A.fritillaria为研究材料,以生长速率为评价指标,对其最适生长温度、pH值、光照、培养基、C及N源的利用等基本培养条件及所产肽类毒素进行了比较研究。研究结果表明,三种菌株最适生长温度有差异,A.pseudoporphyria和A.fritillaria的最适温度为28℃,A.muscaria的最适温度为22℃;A.muscaria菌丝体生长的pH值范围为5-7,另外两个菌株的pH值范围为3-6;24h光照、12h光暗交替和24h黑暗对鹅膏菌的生长速率影响不大;SPDM培养基和MMN培养基都适合三种菌株的生长,但对于A.muscaria来说PDM培养基更适合其生长。鹅膏菌能够利用比较广泛的C、N源,但三个种在利用的C、N源种类上有一定的差别。通过抑芽法实验和HPLC分析分别表明三种鹅膏菌所含肽类毒素在种类和含量上有所不同,但都对绿豆发芽有一定的抑制作用。A.pseudoporphyria和A.fritillaria菌丝体中α-amanitin的含量分别为35.56μg/gDCW(drycellweight细胞干重)和26.02μg/gDCW,不含有phalloidin和β-amanitin;A.muscaria菌丝体中没有检测到α-amanitin、β-amanitin和phalloidin。结果表明供试的三种鹅膏菌在基本培养条件及所产肽类毒素方面存在种水平上的差异。     

Why are defensive toxins so variable? An evolutionary perspective

Defensive toxins are widely used by animals, plants and micro-organisms to deter natural enemies. An important characteristic of such defences is diversity both in the quantity of toxins and the profile of specific defensive chemicals present. Here we evaluate evolutionary and ecological explanations for the persistence of toxin diversity within prey populations, drawing together a range of explanations from the literature, and adding new hypotheses. We consider toxin diversity in three ways: (1) the absence of toxicity in a proportion of individuals in an otherwise toxic prey population (automimicry); (2) broad variation in quantities of toxin within individuals in the same population; (3) variation in the chemical constituents of chemical defence. For each of these phenomena we identify alternative evolutionary explanations for the persistence of variation. One important general explanation is diversifying (frequency- or density-dependent) selection in which either costs of toxicity increase or their benefits decrease with increases in the absolute or relative abundance of toxicity in a prey population. A second major class of explanation is that variation in toxicity profiles is itself nonadaptive. One application of this explanation requires that predator behaviour is not affected by variation in levels or profiles of chemical defence within a prey population, and that there are no cost differences between different quantities or forms of toxins found within a population. Finally, the ecology and life history of the animal may enable some general predictions about toxin variation. For example, in animals which only gain their toxins in their immature forms (e.g. caterpillars on host plants) we may expect a decline in toxicity during adult life (or at least no change). By contrast, when toxins are also acquired during the adult form, we may for example expect the converse, in which young adults have less time to acquire toxicity than older adults. One major conclusion that we draw is that there are good reasons to consider within-species variation in defensive toxins as more than mere ecological noise. Rather there are a number of compelling evolutionary hypotheses which can explain and predict variation in prey toxicity.     

Isolation of B subunit‐specific monoclonal antibody clones that strongly neutralize the toxicity of Shiga toxin 2

Shiga toxin 2 (Stx2)‐specific mAb‐producing hybridoma clones were generated from mice. Because mice tend to produce small amounts of B subunit (Stx2B)‐specific antibodies at the polyclonal antibody level after immunization via the parenteral route, mice were immunized intranasally with Stx2 toxoids with a mutant heat‐labile enterotoxin as a mucosal adjuvant; 11 different hybridoma clones were obtained in two trials. Six of them were A subunit (Stx2A)‐specific whereas five were Stx2B‐specific antibody‐producing clones. The in vitro neutralization activity of Stx2B‐specific mAbs against Stx2 was greater than that of Stx2A‐specific mAbs on HeLa229 cells. Furthermore, even at low concentrations two of the Stx2B‐specific mAbs (45 and 75D9) completely inhibited receptor binding and showed in vivo neutralization activity against a fivefold median lethal dose of Stx2 in mice. In western blot analysis, these Stx2B‐specific neutralization antibodies did not react to three different mutant forms of Stx2, each amino acid residue of which was associated with receptor binding. Additionally, the nucleotide sequences of the V_H and V_L regions of clones 45 and 75D9 were determined. Our Stx2B‐specific mAbs may be new candidates for the development of mouse‐human chimeric Stx2‐neutralizing antibodies which have fewer adverse effects than animal antibodies for enterohemorrhagic Escherichia coli infection.     

贝类非整倍体研究进展

近年来,在贝类多倍体育种研究中,人们发现了成活的非整倍体胚胎和成体,并就此开展了相关的研究.对此研究进行了综述,对非整倍体的类型、产生原因、生长发育、鉴定方法等进行探讨,并展望了非整倍体研究的前景和应用价值.     

Estimating the impact of oyster restoration scenarios on transient fish production

Oyster reef restoration projects are increasing in number both to enhance oyster density and to retain valuable ecosystem services provided by oyster reefs. Although some oyster restoration projects have demonstrated success by increasing density and biomass of transient fish, it still remains a challenge to quantify the effects of oyster restoration on transient fish communities. We developed a bioenergetics model to assess the impact of selected oyster reef restoration scenarios on associated transient fish species. We used the model to analyze the impact of changes in (1) oyster population carrying capacity; (2) oyster population growth rate; and (3) diet preference of transient fish on oyster reef development and associated transient fish species. Our model results indicate that resident fish biomass is directly affected by oyster restoration and oyster biomass, and oyster restoration can have cascading impacts on transient fish biomass. Furthermore, the results highlight the importance of a favorable oyster population growth rate during early restoration years, as it can lead to rapid increases in mean oyster biomass and biomass of transient fish species. The model also revealed that a transient fish's diet solely dependent on oyster reef‐derived prey could limit the biomass of transient fish species, emphasizing the importance of habitat connectivity in estuarine areas to enhance transient fish species biomass. Simple bioenergetics models can be developed to understand the dynamics of a system and make qualitative predictions of management and restoration scenarios.     

Apoptosis inhibitor 5 is an endogenous inhibitor of caspase‐2

Caspases are key enzymes responsible for mediating apoptotic cell death. Across species, caspase‐2 is the most conserved caspase and stands out due to unique features. Apart from cell death, caspase‐2 also regulates autophagy, genomic stability and ageing. Caspase‐2 requires dimerization for its activation which is primarily accomplished by recruitment to high molecular weight protein complexes in cells. Here, we demonstrate that apoptosis inhibitor 5 (API5/AAC11) is an endogenous and direct inhibitor of caspase‐2. API5 protein directly binds to the caspase recruitment domain (CARD) of caspase‐2 and impedes dimerization and activation of caspase‐2. Interestingly, recombinant API5 directly inhibits full length but not processed caspase‐2. Depletion of endogenous API5 leads to an increase in caspase‐2 dimerization and activation. Consistently, loss of API5 sensitizes cells to caspase‐2‐dependent apoptotic cell death. These results establish API5/AAC‐11 as a direct inhibitor of caspase‐2 and shed further light onto mechanisms driving the activation of this poorly understood caspase.     

Skin toxins and external parasitism of coral-dwelling gobies

Toxic ( Gobiodon spp.) and non-toxic ( Paragobiodon xanthosomus ) gobies became infected with external parasites (gnathiid isopods) at equal rates in a laboratory experiment. Parasites were evenly distributed over the body of P. xanthosomus but were mostly confined to the fins of Gobiodon spp., where toxin glands are less abundant. Skin toxins were not associated with the rate of infection but their distribution did appear to influence the site of parasite attachment.     

Visions of Nature and Environmental Sustainability: Shellfish Harvesting in the Dutch Wadden Sea

The concept of sustainability has several, sometimes contrasting, meanings that may generate confusion, misunderstanding, and conflict concerning conservation and restoration practices. It is therefore desirable to clarify the concept of sustainability, thereby potentially contributing to mutual understanding, especially when social conflicts arise. This article discusses a recently published typology of three conceptions of sustainability that range from economic to ecocentric valuations of nature. We argue that the typology is incomplete because it does not include the arcadian approaches. For this reason, we introduce a “tripolar model” for conceptions of sustainability, applying it to the debate on shellfish harvesting in the Dutch Wadden Sea. We conclude that the particular visions or conceptions of sustainability held by relevant actors may have an impact on strategies for conservation.