Sperm chemotaxis in marine invertebrates--molecules and mechanisms

Sperm are attracted by chemical substances which are released by the egg. This process is called chemotaxis. Several molecules that are involved in chemotactic signaling of sperm from marine invertebrates are described and a model of the signaling pathway is presented. We discuss the motor response during chemotaxis and propose a model of the navigation strategy of sperm.     

Chemotaxis in the Marine Fungus Rhizophydium littoreum

Zoospores of the marine chytrid Rhizophydium littoreum are attracted to a variety of substances common to their environment. In general, carbohydrates and polysaccharides elicited strong concentration-dependent positive responses. There was no direct correlation between all substances used as foods and those stimulating positive responses. The chemotactic activities of this organism should, however, tend to bring it toward concentrated food sources.     

Microbial chemotaxis in flowing water in the vicinity of a source of attractant or repellent

Chemotaxis by a population of microbial organisms is studied using two versions of a mathematical model for the chemotactic response to analyze the behavior of marine micro-organisms in flowing water near a source of attractant or repellent. The model yields predictions of the steady-state distributions of the microbial population which may be compared with experiment. A set of laboratory procedures is suggested to provide the data for comparison with the predictions of the model.     

Chemotactic responses of Vibrio alginolyticus to algal extracellular products.

A capillary assay was used to evaluate the chemotactic responses of Vibrio alginolyticus to three common algal extracellular products. Acrylate and glycolate attracted the motile marine bacterium. The peak response occurred with 10(-2) M of each chemical. Acrylic and glycolic acid also attracted V. alginolyticus, with the peak response occurring at 5 x 10(-4) M of each chemical. Higher concentrations of the organic acids resulted in a decreased response. The bacteria also displayed positive chemotaxis to dimethyl sulfide.     

Chemotactic Responses of Marine Vibrio sp. Strain S14 (CCUG 15956) to Low-Molecular-Weight Substances under Starvation and Recovery Conditions

The chemotactic responses by starved cells of marine Vibrio sp. strain S14 differed from those elicited by cells that were not nutrient limited. The rate of chemotaxis at different concentrations of several attractants varied for starved and growing cells. Vibrio sp. strain S14 showed positive chemotaxis to leucine, valine, arginine, and glucose at the onset of energy and nutrient deprivation. A continued, though decreased, positive response was demonstrated fro leucine, arginine, and glucose at 10 h of starvation. Cells starved for 3 h displayed a stronger response to glucose than those starved for shorter or longer times. However, cells starved for 5 and 10 h responded more strongly to a lower concentration of glucose than did cells starved for 0 and 3 h. Starvation for 24 h elicited no measurable chemotaxis to leucine, arginine, or glucose. The motility decreased by over 95% in the cell population after 24 h of starvation, which resulted in a low sensitivity in the chemotaxis assay. A switch in the response to valine was observed by 3 h of starvation. The addition of nutrients of 22-h-starved cells elicited a temporary positive chemotactic response to leucine by 2 and 4 h of nutrient recovery, while cells at 1 and 6 h of recovery showed no response. At 2 h of recovery, the greatest response was recorded to 10⁻⁴ M leucine, whereas at 4 h it was to 10⁻² M leucine. Ten to fifty percent of the 22-h-starved cell population regained their motility after 4 h of nutrient-aided recovery. It is possible that two types of chemosensory systems exist in marine bacteria. Starved and growing cells responded to different concentrations of the attractant, and growing cells displayed a saturated chemotactic system with leucine as the attractant, unlike the response during starvation.     

Different Migration Patterns of Sea Urchin and Mouse Sperm Revealed by a Microfluidic Chemotaxis Device

Chemotaxis refers to a process whereby cells move up or down a chemical gradient. Sperm chemotaxis is known to be a strategy exploited by marine invertebrates such as sea urchins to reach eggs efficiently in moving water. Less is understood about how or whether chemotaxis is used by mammalian sperm to reach eggs, where fertilization takes place within the confinement of a reproductive tract. In this report, we quantitatively assessed sea urchin and mouse sperm chemotaxis using a recently developed microfluidic model and high-speed imaging. Results demonstrated that sea urchin Arbacia punctulata sperm were chemotactic toward the peptide resact with high chemotactic sensitivity, with an average velocity V_x up the chemical gradient as high as 20% of its average speed (238 μm/s), while mouse sperm displayed no statistically significant chemotactic behavior in progesterone gradients, which had been proposed to guide mammalian sperm toward eggs. This work demonstrates the validity of a microfluidic model for quantitative sperm chemotaxis studies, and reveals a biological insight that chemotaxis up a progesterone gradient may not be a universal strategy for mammalian sperm to reach eggs.     

Lack of species-specificity in mammalian sperm chemotaxis

Attraction of spermatozoa by way of chemotaxis to substances secreted from the egg or its surrounding cells has been demonstrated in marine species, amphibians, and mammals. This process is species- or family-specific in marine invertebrates: a chemoattractant for one marine species is usually not recognized by another species or by a member of another family. It is not known whether this selectivity is also the rule in other phyla. Furthermore, it is not at all obvious that such selectivity would be advantageous to species with internal fertilization. Here, using a directionality-based assay for chemotaxis, we studied in vitro the chemotactic response of human and rabbit spermatozoa to human, rabbit, and bovine egg-related factors. We found that spermatozoa from each of the two sources responded similarly well to egg-related factors obtained from any of the three species examined. These results indicate lack of chemotaxis-related, species specificity between these species, suggesting that their sperm chemoattractants are common or very similar. The findings further suggest that mammals do not rely on species specificity of sperm chemotaxis for avoidance of interspecies fertilization.     

Chemotactic response of a marine bacterium to breakdown products of an insoluble substrate

Abstract The basis for this work was to investigate whether bacteria immobilized on or in a solid substrate resulted in the release of low molecular weight products that act as chemoattractants for other bacteria In the surrounding aqueous phase. Chemotaxis of a marine vibrio was observed microscopically along the gradient of breakdown products generated by a Flavobacterium sp. immobilized in an alginate-agar bead. The chemotactic phenomenon was confirmed by a viable counting technique. The chemoattractant was derived from neither the alginate nor the agar but probably was amino acids produced from protein present as a contaminant in the alginate.     

Chemotaxis to chitin oligosaccharides by Vibrio furnissii, a chitinivorous marine bacterium

We have reported that Vibrio furnissii, a chitinivorous marine bacterium, expresses a complex apparatus for adhesion/deadhesion to chitin analogues (1). In the present studies, we show that this organism exhibits a chemotactic response (swarming) to chitin oligosaccharides at concentrations as low as 10 microM. In contrast, V. furnissii exhibits slight to no chemotaxis to other utilizable compounds (glycerol, lactate, amino acids), with the exception of L-glutamic acid. V. furnissii may lack the tar (aspartate) receptor of Escherichia coli.     

Acyl-homoserine lactones modulate the settlement rate of zoospores of the marine alga Ulva intestinalis via a novel chemokinetic mechanism

Bacteria utilize quorum sensing to regulate the expression of cell density-dependant phenotypes such as biofilm formation and virulence. Zoospores of the marine alga Ulva intestinalis exploit the acyl-homoserine lactone (AHL) quorum sensing system to identify bacterial biofilms for preferential settlement. Here, we demonstrate that AHLs act as strong chemoattractants for Ulva zoospores. Chemoattraction does not involve a chemotactic orientation towards the AHL source. Instead, it occurs through a chemokinesis in which zoospore swimming speed is rapidly decreased in the presence of AHLs. The chemoresponse to AHLs was dependant on the nature of the acyl side chain, with N-(3-oxododecanoyl)-homoserine lactone (30-C12-HSL) being the most effective signal molecule. Mean zoospore swimming speed decreased more rapidly over wild-type biofilms of the marine bacteria Vibrio anguillarum relative to biofilms of the vanM mutant, in which AHL synthesis is disrupted. These data implicate a role for AHL-mediated chemokinesis in the location and preferential settlement of Ulva zoospores on marine bacterial assemblages. Exposure to AHLs did not inhibit the negative phototaxis of Ulva zoospores, indicating that chemoattraction to bacterial biofilms does not preclude the response to a light stimulus in substrate location.     

Antibiotic activity of bonellin and hematoporphyrin on marine and terrestrial bacteria

Bonellin, a chlorin extracted fromBonellia viridis (Echiura), and hemaatoporphyrin exhibit a strong antibiotic and bactericidal activity on marine and terrestrial bacteria. This action is enhanced by light. Oxygen consumption and motility of bacteria are also inhibited, while no chemotactic effects are observed. The drugs induce lysis onBacillus subtilis protoplasts, but they are ineffective onMicrococcus lysodeikticus protoplasts.The results are discussed and compared with those obtained with eukariotic cells. Attention is focused on the ecological role of bonellin in the defense mechanism ofBonellia viridis.     

A Non-Poissonian Flagellar Motor Switch Increases Bacterial Chemotactic Potential

We investigate bacterial chemotactic strategies using run-tumble and run-reverse-flick motility patterns. The former is typically observed in enteric bacteria such as Escherichia coli and Salmonella and the latter was recently observed in the marine bacteria Vibrio alginolyticus and is possibly exhibited by other polar flagellated species. It is shown that although the three-step motility pattern helps the bacterium to localize near hot spots, an exploitative behavior, its exploratory potential in short times can be significantly enhanced by employing a non-Poissonian regulation scheme for its flagellar motor switches.     

Bacterial chemotaxis in an optical trap

An optical trapping technique is implemented to investigate the chemotactic behavior of a marine bacterial strain Vibrio alginolyticus. The technique takes the advantage that the bacterium has only a single polar flagellum, which can rotate either in the counter-clock-wise or clock-wise direction. The two rotation states of the motor can be readily and instantaneously resolved in the optical trap, allowing the flagellar motor switching rate S(t) to be measured under different chemical stimulations. In this paper the focus will be on the bacterial response to an impulsive change of chemoattractant serine. Despite different propulsion apparati and motility patterns, cells of V. alginolyticus apparently use a similar response as Escherichia coli to regulate their chemotactic behavior. Specifically, we found that the switching rate S(t) of the bacterial motor exhibits a biphasic behavior, showing a fast initial response followed by a slow relaxation to the steady-state switching rate S0. The measured S(t) can be mimicked by a model that has been recently proposed for chemotaxis in E. coli. The similarity in the response to the brief chemical stimulation in these two different bacteria is striking, suggesting that the biphasic response may be evolutionarily conserved. This study also demonstrated that optical tweezers can be a useful tool for chemotaxis studies and should be applicable to other polarly flagellated bacteria.     

Discovery of 12-(S)-hydroxy-5,8,10,14-icosatetraenoic acid [12-(S)-HETE] in the tropical red alga Platysiphonia miniata

The potent mammalian immunohormone, 12-(S)-hydroxy-5,8,10,14-icosatetraenoic acid (12-(S)-HETE), is a 12-lipoxygenase metabolite of arachidonic acid that is widely distributed in animal tissues. In humans, it is produced and secreted by platelet cells and elicits both chemotactic and degranulatory responses in target neutrophils. As widely as 12-lipoxygenase activity and one of its major products, 12-(S)-HETE, have been found in animal tissues, it has never been found in plants. Herein, we report the first isolation of the 12-lipoxygenase product, 12-(S)-HETE, from a plant, the tropical marine alga Platysiphonia miniata (C. Agardh) B?rgesen.     

A new system for estimating the bacterial cheomotactic response applied to a model oligotrophic marine system

A new system to study bacterial responses is described. The method utilizes a device which consists of a beaker into which funnels with attached membranes are inserted. One funnel exudes a test solution and the other funnel a control solution. Samples were retrieved aseptically at a position one cm below the control and the attractant funnels. A positive chemotactic response by a starved marine Gram-negative bacterium towards mixture of low molecular weight substances was observed. This response was detected during the initial phase of starvation. The model allows the experiments to be carried out under conditions which reflect the situation in natural oligotrophic waters. The possibility to measure subcellular quantities in response to a nutrient concentration was demonstrated by the determinationa of the bacterial fatty acid profile.     

Squid-derived chitin oligosaccharides are a chemotactic signal during colonization by Vibrio fischeri

Chitin, a polymer of N-acetylglucosamine (GlcNAc), is noted as the second most abundant biopolymer in nature. Chitin serves many functions for marine bacteria in the family Vibrionaceae ("vibrios"), in some instances providing a physical attachment site, inducing natural genetic competence, and serving as an attractant for chemotaxis. The marine luminous bacterium Vibrio fischeri is the specific symbiont in the light-emitting organ of the Hawaiian bobtail squid, Euprymna scolopes. The bacterium provides the squid with luminescence that the animal uses in an antipredatory defense, while the squid supports the symbiont's nutritional requirements. V. fischeri cells are harvested from seawater during each host generation, and V. fischeri is the only species that can complete this process in nature. Furthermore, chitin is located in squid hemocytes and plays a nutritional role in the symbiosis. We demonstrate here that chitin oligosaccharides produced by the squid host serve as a chemotactic signal for colonizing bacteria. V. fischeri uses the gradient of host chitin to enter the squid light organ duct and colonize the animal. We provide evidence that chitin serves a novel function in an animal-bacterial mutualism, as an animal-produced bacterium-attracting synomone.     

Cell polarity: an examination of its behavioral expression and its consequences for polymorphonuclear leukocyte chemotaxis

Locomoting polymorphonuclear leukocytes (PMNs) exhibit a morphological polarity. We demonstrate that they also exhibit a behavioral polarity in their responsiveness to chemotactic factor stimulation. This is demonstrated by (a) the pattern of their locomotion in a homogeneous concentration of chemotactic factors, (b) their responses to increases in the homogeneous concentration of chemotactic factors, and (c) their responses to changes in the direction of a chemotactic gradient. The behavioral polarity is not a function of the rate of locomotion of the particular stimulant used to orient the cells, but may reflect an asymmetric distribution of chemotactic receptors or the motile machinery. The polar behavior affects the chemotactic ability of PMNs. The data are discussed in relation to possible mechanisms of sensing a chemotactic gradient.     

Lymphocytes treated with natural alfa-interferon produce a chemotactic factor for human neutrophils

Lymphocytes stimulated with alfa-interferon released a chemotactic factor for neutrophils. The process was not inhibited by cycloheximide, whereas mepacrine completely inhibited release of the chemotactic activity. The chemotactic factor was resistant to storage, heat treatment and proteolysis. Recombinant alfa-interferon did not stimulate lymphocytes to release a neutrophil chemotactic factor.     

Schistosoma japonicum: identification and characterization of neutrophil chemotactic factors from egg antigen

Two neutrophil chemotactic factors were identified in soluble egg antigen preparations of Schistosoma japonicum. The higher-molecular-weight neutrophil chemotactic factor was not separable from eosinophil chemotactic factor by means of gel filtration, anion-exchange chromatography, isoelectric focusing, or affinity chromatography; this neutrophil chemotactic factor is apparently identical to the higher-molecular-weight eosinophil chemotactic factor which we purified previously from the soluble egg antigen. The chemotactic activity of the eosinophil chemotactic factor for neutrophils was stable to periodate oxidation but was notably affected by heating or Pronase digestion, suggesting that the determinant for neutrophil chemotaxis exists on the peptide moiety of the eosinophil chemotactic factor. The lower-molecular-weight neutrophil chemotactic factor was separable from the higher-molecular-weight eosinophil chemotactic factor by gel filtration or anion-exchange chromatography. This neutrophil chemotactic factor was rather hydrophobic and heat-stable, but was sensitive to Pronase or carboxypeptidase A digestion. These results suggest that the receptors on the surfaces of neutrophils and eosinophils for those chemoattractants would be different from each other. We suppose that neutrophil chemotactic factors and eosinophil chemotactic factors from the eggs are responsible for neutrophil and eosinophil accumulation around the eggs in schistosomiasis japonica.     

A bacterial pathogen uses dimethylsulfoniopropionate as a cue to target heat-stressed corals

Diseases are an emerging threat to ocean ecosystems. Coral reefs, in particular, are experiencing a worldwide decline because of disease and bleaching, which have been exacerbated by rising seawater temperatures. Yet, the ecological mechanisms behind most coral diseases remain unidentified. Here, we demonstrate that a coral pathogen, Vibrio coralliilyticus, uses chemotaxis and chemokinesis to target the mucus of its coral host, Pocillopora damicornis. A primary driver of this response is the host metabolite dimethylsulfoniopropionate (DMSP), a key element in the global sulfur cycle and a potent foraging cue throughout the marine food web. Coral mucus is rich in DMSP, and we found that DMSP alone elicits chemotactic responses of comparable intensity to whole mucus. Furthermore, in heat-stressed coral fragments, DMSP concentrations increased fivefold and the pathogen''s chemotactic response was correspondingly enhanced. Intriguingly, despite being a rich source of carbon and sulfur, DMSP is not metabolized by the pathogen, suggesting that it is used purely as an infochemical for host location. These results reveal a new role for DMSP in coral disease, demonstrate the importance of chemical signaling and swimming behavior in the recruitment of pathogens to corals and highlight the impact of increased seawater temperatures on disease pathways.