B. M. Zwicker

Bio: B. M. Zwicker is an academic researcher from Environment Canada. The author has contributed to research in topics: Homarus & Hemolymph. The author has an hindex of 8, co-authored 8 publications receiving 303 citations.

Natural and induced bactericidal activities in the hemolymph of the lobster, Homarus americanus: products of hemocyte-plasma interaction.

Abstract: The salient features of this study of the enhancement of bactericidal activity in the hemolymph of the American lobster were as follows: (a) increase in response to a number of non-pathogens isolated from the lobster's intestinal tract (several pseudomonads, an Achromobacter and Sarcina lutea), (b) one isolate identified as Pseudomonas perolens was used for the bulk of the studies, (c) apparent bactericidal activity of the hemolymph increased severalfold with reduction of the pH of the assay system from the physiological value of 7.6 to a value of 6.0, (d) the extent of the enhancement in vivo was roughly proportional to the concentration of the vaccine, (e) the bactericidal activity's enhancement in vivo was temperature dependent, (f) heat-stability trials indicated the probable presence of more than one bactericidin, (g) the bactericidal principle(s) exists in vivo in an inactive form until activated by material contained within the hemocytes, (h) no protection against Gaffkya homari was conferred on th...

Microbial utilization of the neurotoxin domoic acid: blue mussels (Mytilus edulis) and soft shell clams (Mya arenaria) as sources of the microorganisms

Abstract: The neurotoxin domoic acid is produced in quantity by the diatom Pseudo-nitzschia multiseries and is released to the environment directly and indirectly via food chains. Presumably there is a mecha...

Gaffkemia, a bacterial disease of the lobster, Homarus americanus: effects of the pathogen, Gaffkya homari, on the physiology of the host.

Abstract: Gaffkya homari, the pathogen causing gaffkemia, was observed in vivo to reach its stationary growth phase (approximately 108 bacteria/ml of lobster hemolymph) in 4 days at 15 C. The bacterial totals at death ranged between 5 × 108 and 1 × 1010/ml of hemolymph. Among the main effects of the infection was the great increase in hemolymph clotting times followed by the essential elimination of clotting. The impaired clotting mechanism was a result of the drastic reduction in circulating hemocyte numbers rather than a reduction in hemolymph fibrinogen levels. Hepatopancreatic glycogen levels and hemolymph non-protein nitrogen concentrations dropped to minimal levels but hepatopancreatic lipid levels, hemolymph lactic acid, carbohydrate, and pH values were not significantly affected by the infection. An extreme hyperglycemic effect, attributed to stress, was observed in both control and infected lobsters. Death from gaffkemia, other than that stemming from a wounded animal bleeding to death because of the impai...

Influence of Temperature on Gaffkemia, a Bacterial Disease of the Lobster Homarus americanus

Abstract: The mean time to death for lobsters (Homarus americanus) infected with Gaffkya homari and kept at constant temperatures was 2 days at 20 C, 12 days at 15 C, 28 days at 10 C, 65 days at 7 C, 84 days

The Effects of Harmful Algal Blooms on Aquatic Organisms

Abstract: (2002). The Effects of Harmful Algal Blooms on Aquatic Organisms. Reviews in Fisheries Science: Vol. 10, No. 2, pp. 113-390.

Invertebrate Immunity: Basic Concepts and Recent Advances

Abstract: Publisher Summary This chapter discusses basic concepts and advances of invertebrate immunity. In mammals and other higher vertebrates, a plethora of information exists on the origin, development, structure, and functions of the cells and tissues of the immune system. The cells of the invertebrate immune system can be subdivided into two main groups—namely, the freely circulating blood cells/coelomocytes and a variety of fixed cells. These latter cells may be either scattered throughout the tissues or localized together in hemopoietidphagocytic organs. In addition to these cell-mediated defenses, there are a number of chemical and mechanical barriers to parasite invasion. The chapter also explains the structure and classification of blood cells/coelomocytes. It provides a functional approach for blood cell classification and the cells are arranged into five main groups—namely, progenitor cells, phagocytic cells, hemostatic cells, nutritive cells, and pigmented cells.

Pseudo-nitzschia (Bacillariophyceae) species, domoic acid and amnesic shellfish poisoning: revisiting previous paradigms

Abstract: LELONG A., HEGARET H., SOUDANT P. AND BATES S.S. 2012. Pseudo-nitzschia (Bacillariophyceae) species, domoic acid and amnesic shellfish poisoning: revisiting previous paradigms. Phycologia 51: 168-216. DOI: 10.2216/11-37 Pseudo-nitzschia is a globally distributed diatom genus, some species of which produce domoic acid (DA), the neurotoxin that causes amnesic shellfish poisoning. This toxin killed at least three humans in 1987, launching numerous studies concerning the identification, distribution, ecology and physiology of Pseudo-nitzschia spp. Since previous reviews in 1998, knowledge has been gained about the fate of DA, including its accumulation by marine animals and its degradation by light and bacteria. Molecular techniques and more precise microscopy have enabled the description of new Pseudo-nitzschia species, 15 since 2002, including ones that are cryptic and pseudo-cryptic. An increasing number of the 37 identified species, including oceanic and coastal species, have been studied in laboratory culture. The sexual reproduction of 14 species has been documented. Fourteen species have now been shown to be toxigenic, although some strains are not always toxic under the testing conditions. The biotic and abiotic factors that modify DA production are reviewed, with a focus on how new discoveries have changed our original hypotheses about control mechanisms. Recent studies confirm that silicate and phosphate limitation trigger DA production. However, stress by low concentrations of iron or high concentrations of copper are newly discovered triggers, suggesting a trace-metal chelation role for DA. Organic sources of nitrogen (urea and glutamine), as well as changes in pH, CO2, salinity and bacterial concentration, also enhance DA production. Laboratory and field studies sometimes give divergent results for conditions that are conducive to toxin production. Gaps in knowledge include further information about the whole genome of Pseudo- nitzschia (including sexual stages), mechanisms of DA production and decline, presence or absence of a resting stage, heterotrophic ability, impact of viruses and fungi, and a more complete description of the ecological and physiological roles of DA.

Antimicrobial Peptides from Marine Invertebrates

Abstract: Marine invertebrates lack an acquired, memory-type immunity based on T-lymphocyte subsets and clonally derived immunoglobulins (72). This differs from the vertebrate immune system, which is characterized by somatic gene rearrangement, clonal selection, and expansion and a discriminative ability that includes lymphocytes, among other factors, which impart specificity and memory (71). Marine invertebrates rely solely on innate immune mechanisms that include both humoral and cellular responses. Humoral immunity in marine invertebrates is characterized by antimicrobial agents present in the blood cells and plasma (92), along with reactions such as hemolymph coagulation or melanization (79, 85). Cellular immunity in marine invertebrates is based on cell defense reactions, including encapsulation, nodule formation, and phagocytosis (92). The cellular component of marine invertebrate immunity is mediated by hemocytes, motile cells that phagocytize microbes and secrete soluble antimicrobial and cytotoxic substances into the hemolymph (53). This differs from insects, especially Drosophila melanogaster, which rely largely on the challenge-induced synthesis of antimicrobial peptides by the fat body (30, 88) and use exclusion, via a tough exoskeleton, as their major antimicrobial defense. The circulating hemolymph in marine invertebrates contains biologically active substances such as complement, lectins, clotting factors, and antimicrobial peptides (57). All of these factors contribute to a self-defense system in marine invertebrates against invading microorganisms, which can number up to 106 bacteria/ml and 109 virus/ml of seawater (2). The survival of marine invertebrates in this environment suggests that their innate immune system is effective and robust (52). Antimicrobial peptides are a major component of the innate immune defense system in marine invertebrates. They are defined as molecules less than 10 kDa in mass which show antimicrobial properties (12) and provide an immediate and rapid response to invading microorganisms (8). The major classes of antimicrobial peptides include (i) α-helices, (ii) β-sheet and small proteins, (iii) peptides with thio-ether rings, (iv) peptides with an overrepresentation of one or two amino acids, (v) lipopeptides, and (vi) macrocyclic cystine knot peptides (24). There is evidence that antimicrobial peptides are widespread in invertebrates (15), especially in tissues such as the gut and respiratory organs in marine invertebrates, where exposure to pathogenic microorganisms is likely. In spite of variations in structure and size, the majority of antimicrobial peptides are amphiphilic, displaying both hydrophilic and hydrophobic surfaces. These peptides generally act by forming pores in microbial membranes or otherwise disrupting membrane integrity (82), which is facilitated by their amphiphilic structure. This mode of action is unlikely to lead to the development of resistance (9, 58), although it must be noted that this presumption is debatable (10). Recently, cationic antimicrobial peptides have been reported to be involved in many aspects of innate host defenses, associated with processes such as acute inflammation (25). The value of antimicrobial peptides in innate immunity lies in their ability to function without either high specificity or memory, and their small size makes them easy to synthesize (72). In addition, many antibacterial peptides show remarkable specificity for prokaryotes with low toxicity for eukaryotic cells (97). This is a characteristic that has favored their investigation and exploitation as potential new antibiotics (97). The recent appearance of a growing number of bacteria resistant to conventional antibiotics has become a serious medical problem. To overcome this resistance, the development of antibiotics with novel mechanisms of action is a pressing issue (48). Endogenous antimicrobial peptides are exciting candidates as new antibacterial agents due to their broad antimicrobial spectra, highly selective toxicities, and the difficulty for bacteria to develop resistance to these peptides (11, 26, 47). The ocean covers 71% of the surface of the earth and contains approximately half of the total global biodiversity, with estimates ranging between 3 and 500 × 106 different species (28). Marine macrofauna alone comprise 0.5 to 10 × 106 species (23). Therefore, the marine environment, especially marine invertebrates that rely solely on innate immune mechanisms for host defense, is a spectacular resource for the development of new antimicrobial compounds. This minireview will encompass what is known about gene-encoded antimicrobial peptides from marine invertebrates, covering the phyla Arthropoda, Chordata, and Mollusca (Table ​(Table11). TABLE 1. Antimicrobial peptides from marine invertebrates