Chemotactic and chemokinetic activities of <Emphasis Type="Italic">Saprolegnia parasitica</Emphasis> toward different metabolites and fish tissue extracts

 The chemotactic and chemokinetic activities in zoospores of Saprolegnia parasitica NJM 8604 (= H2) were examined using various amino acids, carbohydrates, fatty acids, and fish tissue extracts to estimate one of the important factors for attachment of zoospores to their host. All the tested six amino acids showed strong chemotactic reactions whereas carbohydrates and fatty acids caused moderate or strong chemotactic reactions. The chemokinetic activities against amino acids and carbohydrates were moderate or weak, whereas almost all fatty acids showed negative chemokinetic responses. Almost all tested fish tissue showed moderate chemotactic response and weak or moderate chemokinetic responses. Generally, chemotactic activity was strong in the amino acids, and the strongest activity was observed in alanine. Based on these facts, we considered that zoospores may react against amino acids of the fish body to attach and establish their colonization. Received: January 10, 2001 / Accepted: December 12, 2002 Correspondence to:K. Hatai     

Zoospore production and motility of mangrove thraustochytrids from Hong Kong under various salinities

We investigated the effects of salinity on the zoospore production of four mangrove thraustochytrid isolates, Schizochytrium sp. KF1, Aurantiochytrium mangrovei KF6, Thraustochytrium striatum KF9 and Ulkenia sp. KF13. The zoospore motilities, which were based on curvilinear velocity (VCL) and straight-line velocity (VSL), were monitored using the Computer-Assisted Sperm Motility Analysis (CASA) Software system. The zoospore production of four isolates was suppressed at salinity above 15‰. Schizochytrium sp. produced the greatest number of zoospores at 15‰, while Aurantiochytrium mangrovei and Ulkenia sp. produced abundant zoospores in diluted sea water ranging from 7.5 to 15‰. Thraustochytrium striatum performed relatively poorly under all salinities. Salinity and exposure time, as well as their interactions, had significant impacts on most zoospore velocity measurements. The optimal velocities of zoospore motility also varied among isolates. Zoospores of Schizochytrium sp. and A. mangrovei had similar responses to salinity, with the highest motility at 7.3‰, followed by a decrease in velocities with increasing salinity. In contrast, the zoospore of T. striatum had optimal motility at 12‰ and remained highly motile from 15 to 20‰. The velocities of zoospores of Ulkenia sp. were the lowest among the tested thraustochytrids and had optimal motility at 12‰. Zoospores of all the isolates remained active after 4 h of exposure to aqueous medium, but the optimal salinity for each mode of swimming changed. The ecological significance of these data are discussed.     

Zoospore chemotaxis in Australian isolates of Phytophthora species.

Zoospores of Australian isolates of Phytophthora drechsleri, P. cryptogea, P. cinnamomi, P. nicotianae var. parasitica, and P. citricola were examined for their chemotactic responses to asparagine, glutamine, aspartate, glutamate, and structurally related compounds. Structural requirements for attraction include the alpha-amino-acid group with a short carbon chain terminating in an amide group. The one American isolate tested gave a different result and possible reasons for this are discussed. The pH of the environment was important, a neutral-charged molecule was more attractive than a negatively charged molecule, hence glutamine and aspartate were more attractive at pH 3.0 than pH 5.0. Zoospores tended to move away from regions with a high hydrogen ion concentration. Compounds other than amino acids were slightly attractive including several sugars and ethanol. Synergistic interactions between amino acids, ethanol, and sucrose were observed and may account for the high levels of attraction of zoospores to root exudates and extracts.     

Photoresponses of the marine protist Ulkenia sp. zoospores to ambient, artificial and bioluminescent light

Ulkenia sp. zoospores are attracted to 492 nm wavelength light produced by the marine bacterium Vibrio fischeri. Zoospores are positively photoresponsive to wavelengths of 440, 460 and 480 nm and contain a pigment that absorbs blue light. The average velocity of the zoospores is 0.47 m h(-1). Stimulatory intensities of these wavelengths ranged from 0.5 to 3.5 μEm(-2) s(-1) in both laboratory and field studies. The response of this protist to bioluminescence produced by Vibrio fischeri may direct zoospores to a nutrient rich environment colonized by these bacteria. In addition, the greatest responses were found at intensities associated with the light regime found near the bottom of naturally turbid estuaries or at greater depths of nonturbid, offshore waters. Positive phototaxis was not seen in zones of high light intensity either in field or laboratory studies, and there is some indication that zoospores may swim away from high light intensities.     

Chemotaxis of Bradyrhizobium japonicum to various organic compounds

The investigation of the chemotactic response of Bradyrhizobium japonicum to amino acids, carbohydrates, multiatomic alcohols, organic acids, and soybean extracts showed that the extracts of some soybean varieties (Chernoburaya and Beskluben'kovaya) contain repellents. This indicates that the soybeans of host plants contain effectors that may play a role at the early stages of their interaction with nodule bacteria.     

The Chemotactic Response of Bradyrhizobium japonicum to Various Organic Compounds

The investigation of the chemotactic response of Bradyrhizobium japonicum to amino acids, carbohydrates, multiatomic alcohols, organic acids, and soybean extracts showed that the extracts of some soybean varieties (Chernoburaya and Beskluben'kovaya) contain repellents. This indicates that the soybeans of host plants contain effectors that may play a role at the early stages of their interaction with nodule bacteria.     

Chemical characterization of root exudates from rice (Oryza sativa) and their effects on the chemotactic response of endophytic bacteria

Root exudates represent an important source of nutrients for microorganisms in the rhizosphere and seem to participate in early colonization inducing chemotactic responses of rhizospheric bacteria. We characterized the root exudates collected from rice plantlets cultured under hydroponic conditions and assessed their effects on the chemotaxis of two strains of endophytic bacteria, Corynebacterium flavescens and Bacillus pumilus, collected from the rice rhizosphere. We compared these chemotactic effects on endophytic bacteria with those on two strains of plant-growth-promoting bacteria, Azospirillum brasilense (isolated from the corn rhizosphere) and Bacillus sp. (from the rice rhizosphere). The root exudates were collected at different time intervals. The highest concentration and diversity of amino acids and carbohydrates were found during the first 2 weeks after seeding. Histidine, proline, valine, alanine, and glycine were the main amino acid residues identified during the 4 weeks of culture. The main carbohydrates identified were glucose, arabinose, mannose, galactose, and glucuronic acid. The chemotactic responses of the analyzed endophytic bacteria to root exudates were 3.9 to 5.1 times higher than those of A. brasilense and 2.2 to 2.8 times higher than Bacillus sp. Our results indicate that rice exudates may induce a higher chemotactic response for endophytic bacteria than for other bacterial strains present in the rice rhizosphere.     

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.     

Studies on the chemoreception of the nemertean, Procephalothrix simulus Iwata, 1952

The feeding responses of Procephalothrix simulus Iwata to the whole-body extracts of different animals (Tubifex sp., Saccocirrus gabrillae) and single compounds (including 17 amino acids, 2 compounds related to amino acids and 2 sugars) were tested, and the response of the nemerteans with and without a frontal organ to stimulus was compared experimentally. Results showed that P. simulus is able to detect food from a distance by chemoreception. It preferred extracts to live prey, and boiled extracts were more attractive than extracts that were not boiled. Of the 21 compounds tested, 6 amino acids (glycine, alanine, isoleucine, phenylalanine, glutamine, asparagine) and betaine induced a feeding response, suggesting that they were possibly the chemical signals in the food location of P. simulus. When the frontal organ was removed, P. simulus apparently lost its selectivity, which indicated that in this nemertean chemoreception for the detection of prey was performed by the frontal organ.     

Influence of foliar application of pesticides on leaf extracts and phylloplane microflora of corn

The effect of foliar application of captan, dithane, carbaryl and atrataf on the quantity of total carbohydrates, total amino acids and total nitrogen leached from corn leaves and on the phylloplane counts of fungi, bacteria and actinomycetes was studied. Leaf extracts were analyzed for amino acids, carbohydrates and nitrogen and were correlated with microbial counts. Generally the microbial counts were less than the control in treated samples and a significant change in Gram-negative bacteria in all treatments was recorded. All treated leaf extracts showed less total amino acids and total nitrogen though they were rich in carbohydrates as compared with the control.     

六种固氮蓝藻提取液对玉米的促长作用和提取液成分比较

本文用六种固氮蓝藻的提取液处理玉米种子,同时对其提取液氨基酸组成和碳水化合物与维生素Ｂ１２的含量进行了分析。结果表明固氮鱼腥藻ＨＢ６８６（ＡｎａｂａｅｎａａｚｏｔｉｃａＨＢ６８６）、球孢鱼腥藻ＨＢ１０１７（Ａ．ｓｐｈａｅｒｉｃａＨＢ１０１７）、多变鱼腥藻ＨＢ１０５８（Ａ．ｖａｒｉａｂｉｌｉｓＨＢ１０５８）和小单歧藻ＨＢＴＴ（ＴｏｌｙｐｏｔｈｒｉｘｔｅｎｕｉｓＨＢＴＴ）的提取液中氨基酸、碳水化合物和维生素Ｂ１２的含量高于鱼腥藻ＳＰ．ＨＢ１０４２（Ａｎａｂａｅｎａｓｐ．ＨＢ１０４２）和繁育管链藻ＨＢ３８（ＡｕｌｏｓｉｒａｆｅｒｔｉｌｉｓｓｉｍａＨＢ３８）。同时,促进玉米种子萌发和幼苗生长的效果前四种藻较好,后两种则较差。     

Motility and Chemotaxis in Zoospores of Phytophthora palmivora (Butl.) Butl.

Zoospores of Phytophthora palmivora were motile for 84 h indistilled water at the optimum temperature, 17 °C. Motilitytime was markedly reduced by high zoospore density, by CaCl₂,MgSO₄.7H₂O, glutamine, glucose, by buffer solutions and by frequentcontact of zoospores with solid surfaces. The zoospores encystedinstantly and disintegrated at pH 2.2–5.0 and in 1.0 mMCuSO₄ and FeCl₂ and 1.0 per cent (w/v) peptone solutions. Velocityof movement increased as the temperature rose from 8 to 33 °C. The zoospores responded chemotactically to an extract of cocoapod but not to the exudate. Amino acids of the extract as wellas other amino acids and sugars individually attracted the zoospores.Attracted zoospores quickly encysted and germinated; the germtubes were uniformly directed towards source of stimulus.     

Chemotaxis ofRhizobium sp. Towards root exudate ofCicer Arietinum L.

Summary Root exudate from seedlings ofCicer arietinum L. was collected in a chamber under aseptic conditions. The exudate was fractionated into anion, cation and neutral fractions. The anionic fraction was made up of galacturonic acid, gluconic acid, mannuronic acid and two unidentified compounds withR _f values 0.56 and 0.62. The cationic fraction contained alanine, arginine, aspartic acid, cystine, glycine, histidine, isoleucine, leucine, lysine and serine. The neutral fraction was made up of arabinose, galactose, glucose, ribose and xylose. The amino acids contributed to the bulk of the root exudate. The ratio of anionic, cationic and neutral fraction was 1∶7∶2. The crude root exudate was tested for its chemotactic ability using the capillary tube method. It was highly chemotactic for theRhizobium sp. The individual fractions and their various combinations were tested for chemotaxis. The chemotactic response of the Cicer strain of Rhizobium was least with anionic fraction most with cationic fraction and intermediate with neutral fraction. Maximum chemotactic response among the fractional combinations was obtained with all the three fractions and least with cationic plus neutral factions. Individual compounds constituting the various fractions were also tried for their ability to elicit chemotactic response. The organism exhibited maximum positive chemotactic response to histidine and negative response to alanine among the amino acids and to glucose and gluconic acid among the sugars and sugar acids.     

A rumen anaerobic fungus of the genus Neocallimastix: ultrastructure of the polyflagellate zoospore and young thallus

The ultrastructure of the zoosporic, rumen fungal anaerobe, Neocallimastix sp. R1, was determined and compared to that of the two known species of Neocallimastix. Zoospores of the new isolate were generally ovoid in shape, but without the waisted appearance of N. frontalis zoospores. They possessed similar organelles to the other two species, but with different localisation. The flagellar rootlet system was broadly similar to N. frontalis and N. patriciarum, however, a previously undescribed, large organelle was found to be associated near the kinetosomal apparatus in some Neocallimastix sp. R1 zoospores. Well developed flagella, complete with basal bodies, were observed in young thalli.     

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.     

Chemoreception in the green algaDunaliella tertiolecta

A capillary assay was employed to quantify positive chemotactic responses in the motile, unicellular, marine algaDunaliella tertiolecta. Among a wide range of inorganic and organic compounds tested, only ammonium ion,l-tyrosine,l-tryptophan, andl-phenylalanine were found to be major atractants for the chlorophyte.l-Methionine andl-cysteine weakly attracted the alga at 10⁻³ M. The minimum concentration of the major attractants needed to elicit an observable chemotactic response was approximately 10⁻⁶ M. The maximum response occurred when the capillaries contained 10⁻⁵ Ml-tyrosine orl-tryptophan, 10⁻⁴ Ml-phenylalanine, and 10⁻³ M ammonium chloride. The other amino acids, carbohydrates, B-vitamins, urea, and nitrate were among the chemicals that failed to attractD. tertiolecta. The alga apparently possesses one chemoreceptor that binds ammonium ion only, and another chemoreceptor that binds the three aromatic amino acids.     

Fungitoxic effects of nonprotein imino acids on growth of saprophytic fungi isolated from the leaf surface of Calliandra haematocephala

Four saprophytic and pathogenic fungi were isolated from the leaf surface of Calliandra haematocephala, a tropical legume known to contain large amounts of rare nonprotein imino acids in its leaves and seeds. The fungi Aspergillus niger, Aspergillus sp., Curvularia sp., and Penicillium sp. were cultured in the laboratory and tested for susceptibility to leaf extracts of the host plant and to proline, pipecolic acid, cis-5-hydroxypipecolic acid, and 2,4-trans-4,5-cis-4,5-dihydroxypipecolic acid. Fungal spore germination and germ tube growth were measured. Aspergillus sp. was inhibited by plant extracts and by pipecolic acid and cis-5-hydroxypipecolic acid. Curvularia sp. growth was stimulated by plant extracts and by pipecolic acid. The other two fungi were unaffected by any of the treatments. The data indicate that imino acids may play a role in the specific resistance of Calliandra spp. to Aspergillus sp.     

Fungitoxic effects of nonprotein imino acids on growth of saprophytic fungi isolated from the leaf surface of Calliandra haematocephala.

Four saprophytic and pathogenic fungi were isolated from the leaf surface of Calliandra haematocephala, a tropical legume known to contain large amounts of rare nonprotein imino acids in its leaves and seeds. The fungi Aspergillus niger, Aspergillus sp., Curvularia sp., and Penicillium sp. were cultured in the laboratory and tested for susceptibility to leaf extracts of the host plant and to proline, pipecolic acid, cis-5-hydroxypipecolic acid, and 2,4-trans-4,5-cis-4,5-dihydroxypipecolic acid. Fungal spore germination and germ tube growth were measured. Aspergillus sp. was inhibited by plant extracts and by pipecolic acid and cis-5-hydroxypipecolic acid. Curvularia sp. growth was stimulated by plant extracts and by pipecolic acid. The other two fungi were unaffected by any of the treatments. The data indicate that imino acids may play a role in the specific resistance of Calliandra spp. to Aspergillus sp.     

Phytophthora parasitica biofilm formation: installation and organization of microcolonies on the surface of a host plant

Zoospores of the oomycete Phytophthora parasitica establish microbial spheroid microcolonies and biofilms on the surface of wounded leaves of their host, Nicotiana tabacum . The formation of microcolonies involves the movement of some zoospores towards attractants from wound sites, followed by their irreversible adsorption and the formation of a cluster of cells. These cells drive the migration of a second wave of zoospores (several hundreds cells) by setting up an external chemotactic gradient leading to massive zoospore encystment and cyst-orientated germination. Zoospores that are still swimming at this stage circulate within the nascent biofilm by opening channels. Concomitantly, the cell population secretes various substances to elaborate an extracellular mucilage. Embedded within the extracellular matrix, biofilm cells are organized into a structured community as coacervates. The granular surface is composed of individual cysts, located on the outside of the microcolony. Hyphae from these cysts plunge downwards towards the dense core formed by the founder cells. This report is the first to show the installation and organization of a biofilm formed by eukaryotic cells on plant surfaces. The P. parasitica microcolonies constitute heterogeneous microenvironments for the embedded and circulating cells. They may affect plant–pathogen interactions by serving as reservoirs for pathogenic microorganisms, as protecting niche against host defences or as structures for infecting populations.