PubMed Health⌕ Search

Biomedical subjects

M Levandowsky

Publications and source records attributed to M Levandowsky.

9 recordsLinked to original sources
PubMed1979

Unity and diversity in biochemistry.

A consideration of A Biochemical Phylogeny of the Protists, by M.A. Ragan and D.J. Chapman (Academic Press, 1978) and Biochemical Adaptation to Environmental Change, ed. by R.M.S. Smellie and J.F. Pennock (the Biochemical Society, 1976), within some thoughts on biochemical evolution.

Animals↗
PubMed1975

Ultrasensitive chemosensory responses by a protozoan to epinephrine and other neurochemicals.

A behavioral assay was developed based on differential tendency of a protozoan to attach to an agar gel containing the test substance. The heterotrophic marine dinoflagellate Crypthecodinium (Gyrodinium) cohnii responded negatively (less tendency to attach) to epinephrine at concentrations above 5 X 10(-15)M and to norepinephrine at concentrations above 5 X 10(-9)M. Response to choline as choline H2 citrate, choline bitartrate, and choline chloride was negative above 10(-7)M, but response to the choline analog carbachol was positve (greater tendency to attach) in the range 5 X 10(-6) to 5 X 10(-4)M. Other responses to neurochemicals at comparable concentrations were: dopa, betaine, and glycine--positive; L-glutamic acid, tryptophan, putrescine, and taurine--negative. Serotonin was inert, responses to tyrosine and gamma-aminobutyric acid were variable, and phenylalanine (6 X 10(-3)M) and 5-hydroxytryptophan (5 X 10(-4)M) were negative only at the highest concentrations tested.

5-Hydroxytryptophan↗
PubMed1975

Utilization of Fe3+ by the inshore colorless marine dinoflagellate Crypthecodinium cohnii.

A Puerto Rican isolate of the colorless dinoflagellate Crypthecodinium cohnii was grown in a defined marine medium. Fe was added as Fe(NH4)2(SO3)2 - 6H2O (2.0 mg%), FeCl3 - 6H2O (1.0 mg%) or a particulate slurry prepared from FeCl3 + KOH, along with varying concentrations of several chelators. Heavy growth at pH 7.5-7.7 occurred with salicylhydroxamic acid, aurintricarboxylic acid, EDTA, NTA, and humic acid; and at pH 7.9-8.1 with SHAM and ATA. Moderate growth occurred at pH 7.5-7.7 with sulfosalicylic acid, dipicolinic acid, pyrocatecholdisulfonic acid, hexanohydroxamic acid, L-histidine, and at pH 7.9-8.1 with 1-naphthohydroxamic acid, EDTA, NTA. Slight growth occurred at pH 7.5-7.7 with benzohydroxamic acid, 1-naphohydroxamic acid, 2.6-dipicolinic acid N-oxide, salicylic acid, rhodotorulic acid, Na oxalate, EDDHA, sorbohydroxamic acid, gamma-pyrone-2, 6-decarboxylic acid, and at pH 7.9-8.1 with hexanohydroxamic acid, benzohydroxamic acid. Some ecological and physiological implications are discussed.

Aurintricarboxylic Acid↗
PubMed1975

A mathematical model of pattern formation by swimming microorganisms.

Bioconvection in suspensions of Tetrahymena pyriformis and Crypthecodinium cohnii is described and 2 new patterns, the toroid and the cat's-eye, which appear in shallow suspensions of C. cohnii, are reported. Except in very dense cultures, bioconvection does not arise unless the depth of the suspensions or the mean concentration exceed certain critical values, other things being equal. A mathematical model describing the hydrodynamics of suspension of negatively geotactic microorganisms is described which predicts the existence of critical depths and concentrations. The equations presented admit solutions describing the "polka-dot" patterns seen at low organism concentration in suspensions slightly deeper than the critical value. The discussion here is limited to the case of fairly dilute suspensions, but the basic approach can be applied also to richer cultures.

Dinoflagellida↗
PubMed1975

Chemosensory responses of a protozoan are modified by antitubulins.

Modification of a behavioral response of a marine dinoflagellate to chemical cues is described. Negative response to choline was modified by the antitubulins vincristine, vinblastine, griseofulvin, and trifluralin, but not by colchicine. Positive responses to 3,4-dihydroxyphenylalanine were unaffected by these drugs.

Chemotaxis↗
PubMedDate not supplied

Chemosensory responses of Acanthamoeba castellanii: visual analysis of random movement and responses to chemical signals.

A visual assay slide chamber was used in conjunction with time-lapse videomicroscopy to analyze chemotactic behavior of axenically grown Acanthamoeba castellanii. Data were collected and analyzed as vector scatter diagrams and cell tracks. Amebas responded to a variety of bacterial products or potential bacterial products by moving actively toward the attractant. Responses to the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide, and lipid A were statistically significant (P < or = 0.03), as was the response to fMLP benzylamide (P < or = 0.05). Significant responses to cyclic AMP, lipoteichoic acid, and N-acetyl glucosamine were also found. Chemotactic peptide antagonists, mannose, mannosylated bovine serum albumin, and N-acetyl muramic acid all yielded nonsignificant responses (P > 0.05). There was no single optimal concentration for response to any of the attractants tested, and amebas responded equally over the range of concentrations tested. Pretreatment of amebas with chemotactic peptides, bacterial products, and bacteria reduced the directional response to attractants. Amebas that had been grown in the presence of bacteria appeared more responsive to chemotactic peptides. Treatment of amebas with trypsin reduced the response of cells to chemotactic peptides, though sensitivity was restored within a couple of hours. This suggests the ameba membrane may have receptors, sensitive to these bacterial substances, which are different from the mannose receptors involved in binding bacteria to the membrane during phagocytosis. The rate of movement was relatively constant (ca. 0.40 microns/s), indicating that the locomotor response to these signals is a taxis, or possibly a klinokinesis, but not an orthokinesis. Studies of the population diffusion rate in the absence of signals indicate that the basic population motility follows the pattern of a Levy walk, rather than the more familiar Gaussian diffusion. This suggests that the usual mathematical models of ameboid dispersion may need to be modified.

Acanthamoeba↗