Lampyridae (Coleoptera): A plethora of mollicute associations

Beetles (Coleoptera) harbor many species ofAcholeplasma andSpiroplasma (division Tenericutes, class Mollicutes). Mollicutes were isolated from guts and/or hemocoels of firefly beetles (Lampyridae) from the United States (Maryland and West Virginia), Ecuador, and Tobago. Firefly beetles were frequent hosts for the group XIV spiroplasma, isolated from Ellychnia corrusca, and the group XIX spiroplasma, isolated fromPhoturis spp. The most unusual feature of the firefly-mollicute association is the carriage of four Mycoplasma species. Recent phylogenetic studies indicate that these species are members of a clade that includes a vertebrate pathogen,Mycoplasma mycoides. The high rate of occurrence ofMycoplasma species (which are, otherwise, infrequent in insects) in lampyrid beetles suggests that the association is significant. The unusual light-producing physiology of lampyrids (which is dependent on large pools of energy) and the production of large amounts of cardenolides from cholesterol (a critical growth factor for many mollicutes) may favor colonization by mollicutes. Offprint requests to: K. J. Hackett.     

Enhancement of oxygen mass transfer in stirred bioreactors using oxygen-vectors. 1. Simulated fermentation broths

Oxygen mass transfer represents the most important parameter involved in the design and operation of mixing-sparging equipment for bioreactors. It can be described and analyzed by means of the mass transfer coefficient, k_La. The k_La values are affected by many factors such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganism morphology, and biocatalysts properties. The efficiency of oxygen transfer could be enhanced by adding oxygen-vectors in broths, such as hydrocarbons or fluorocarbons, without increasing the energy consumption for mixing or aeration. The experimental results obtained for simulated broths indicated a considerable increase of k_La in the presence of n-dodecane, and the existence of a certain value of n-dodecane concentration that corresponds to a maximum mass transfer rate of oxygen. The magnitude of the positive effect of n-dodecane depends both on the broths characteristics and operational conditions of the bioreactor.Notation d stirrer diameter, mm - d oxygen electrode diameter, mm - D bioreactor diameter, mm - h distance from the inferior stirrer to the bioreactor bottom, mm - H bioreactor height, mm - k_La oxygen mass transfer coefficient, s^-1 - l impeller blade length, mm - I oxygen electrode immersed length, mm - P power consumption for mixing of non-aerated broths, W - P_a power consumption for mixing of aerated broths, W - (P_a/V) specific power input, W/m³ - s baffle width, mm - v_S superficial air velocity, m/s - V volume of medium, m³ - w impeller blade height, mm - volumetric fraction of oxygen-vector - _a apparent viscosity, Pa*s - density, kg/m³     

Two-dimensional ultrastructural elements lead to three-dimensional reconstruction of protuberances on the cocoon membrane of the leech, Theromyzon tessulatum

Protuberances on the cocoon surface of the leech, Theromyzon tessulatum, are roughly parallel rows of triangular prisms arranged equidistantly to each other on the outer surface of the cocoon membrane. The distance between neighboring protuberances is approximately 1.6 microm, the height approximately 0.5 microm and the semi-width approximately 0.3 microm. The fibrillar arrangement within the protuberance maintains some elements of the helicoids found within the cocoon membrane but a high proportion of large holes disrupt the symmetry of the protuberance ultrastructure. A procedure for 3D reconstruction of the protuberance using the complementarity between the paratangential and normal sections through the cocoon is presented. Our results demonstrate that the ultrastructure of protuberances show elements of a twisted fibrillar arrangement, but the demands of filling a narrow space ruled by acute angles appears to cause a high degree of ultrastructural disorganization.     

Dietary Docosahexaenoic Acid Supplementation Modulates Hippocampal Development in the Pemt?/? Mouse

The development of fetal brain is influenced by nutrients such as docosahexaenoic acid (DHA, 22:6) and choline. Phosphatidylethanolamine-N-methyltransferase (PEMT) catalyzes the biosynthesis of phosphatidylcholine from phosphatidylethanolamine enriched in DHA and many humans have functional genetic polymorphisms in the PEMT gene. Previously, it was reported that Pemt^−/− mice have altered hippocampal development. The present study explores whether abnormal phosphatidylcholine biosynthesis causes altered incorporation of DHA into membranes, thereby influencing brain development, and determines whether supplemental dietary DHA can reverse some of these changes. Pregnant C57BL/6 wild type (WT) and Pemt^−/− mice were fed a control diet, or a diet supplemented with 3 g/kg of DHA, from gestational day 11 to 17. Brains from embryonic day 17 fetuses derived from Pemt^−/− dams fed the control diet had 25–50% less phospholipid-DHA as compared with WT (p < 0.05). Also, they had 60% more neural progenitor cell proliferation (p < 0.05), 60% more neuronal apoptosis (p < 0.01), and 30% less calretinin expression (p < 0.05; a marker of neuronal differentiation) in the hippocampus compared with WT. The DHA-supplemented diet increased fetal brain Pemt^−/− phospholipid-DHA to WT levels, and abrogated the neural progenitor cell proliferation and apoptosis differences. Although this diet did not change proliferation in the WT group, it halved the rate of apoptosis (p < 0.05). In both genotypes, the DHA-supplemented diet increased calretinin expression 2-fold (p < 0.05). These results suggest that the changes in hippocampal development in the Pemt^−/− mouse could be mediated by altered DHA incorporation into membrane phospholipids, and that maternal dietary DHA can influence fetal brain development.     

Spiroplasma Species, Groups, and Subgroups from North American Tabanidae

Twenty-one triply cloned spiroplasma strains from the United States east of the Rocky Mountains, all isolated from tabanid (Diptera:Tabanidae) flies or serologically related to strains from tabanids, were compared reciprocally by spiroplasma deformation (DF) and metabolism inhibition (MI) serological tests. Many of the strains were also tested against 28 antisera representing known spiroplasma groups, subgroups, and putative groups isolated from nontabanid hosts. Relationships among strains were indicated by reciprocal cross-reactivity in both DF and MI tests. The strains were found to represent 11 recognized spiroplasma groups or subgroups. On the basis of serological, biochemical, and genomic data, strain BARC 1901 from Tabanus lineola appeared to represent a previously unrecognized candidate group. Strain BARC 2649, also from T. lineola, also appeared to represent a new group, but its morphology, arginine utilization, and some one-way serological crossing patterns suggested that it may be distantly related to group VIII spiroplasmas. Morphological, serological, and genomic data were used to place tabanid spiroplasma strains into three informal clusters. These are (i) groups IV (strain B31) and XXXI (strain HYOS-1); (ii) the three existing subgroups and a new candidate subgroup of group VIII represented by strain BARC 1357 plus ungrouped strain BARC 2649; and (iii) 14 strains, including EC-1 and TATS-1 (group XIV); strains TN-1 and TAAS-2 (group XVIII); strains TG-1, TASS-1, and BARC 4689 (group XXIII), strains TALS-2 (group XXVII), strain TABS-2 (group XXXII), and strains TAUS-1 and TABS-1 (group XXXIII) and ungrouped but closely related strains BARC 1901, BARC 2264 and BARC 2555. Analysis of tabanids from other geographic regions probably will substantially increase the number of known spiroplasma groups from this insect family. Received: 23 April 1997 / Accepted: 31 May 1997     

Mycoplasma somnilux sp. nov., Mycoplasma luminosum sp. nov., and Mycoplasma lucivorax sp. nov., new sterol-requiring mollicutes from firefly beetles (Coleoptera: Lampyridae)

Strain PYAN-1T (T = type strain), which was isolated from a pupal gut of the firefly beetle Pyractonema angulata, and strains PIMN-1T and PIPN-2T, which were isolated from guts of adult Photinus marginalis and Photinus pyralis fireflies, respectively, were demonstrated to be sterol-requiring mollicutes. Cells of the three strains were shown by electron and dark-field microscopy to be small, pleomorphic, nonhelical, nonmotile bodies surrounded by single membranes. No evidence of a cell wall was observed, and the organisms were not susceptible to 500 U of penicillin per ml. The three strains grew rapidly in SP-4 broth medium. Strains PIMN-1T and PIPN-2T grew in medium supplemented with bovine serum fraction, but strain PYAN-1T did not. All three strains grew on solid media when the cultures were incubated aerobically, but only strains PYAN-1T and PIPN-2T formed colonies when anaerobic conditions were employed. The three strains catabolized glucose but hydrolyzed neither arginine nor urea. All of the strains grew at temperatures of 18 to 32 degrees C; strains PYAN-1T and PIMN-1T also grew at 10 degrees C. The optimal temperature for growth for strains PYAN-1T and PIPN-2T was 30 degrees C; strain PIMN-1T grew equally well at 30 or 32 degrees C. None of the three strains grew at 37 degrees C. The genome sizes of strains PYAN-1T, PIMN-1T, and PIPN-2T were about 527 (478 to 589), 570 (480 to 630), and 762 (635 to 871) megadaltons, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

The inhibition of alcohol dehydrogenase in vitro and in isolated hepatocytes by 4-substituted pyrazoles

As a means of comparing the functional properties of an enzyme in dilute solution in vitro with those for the same enzyme acting in its normal cellular environment, a study was conducted with 4-substituted pyrazoles as inhibitors of rat liver alcohol dehydrogenase in vitro and ethanol oxidation in isolated rat hepatocytes. Inhibitor constants (Ki's) for the same set of pyrazole derivatives were also determined for human liver alcohol dehydrogenase. The best-fitting equations were derived to relate the Ki's to the chemical nature of substituents. These quantitative structure-activity relationships show that pyrazoles with stronger electron-withdrawing substituents are weaker inhibitors both for the enzyme in vitro and, to an equal extent, for ethanol oxidation by intact cells. Inhibitor effectiveness is also dependent on substituent hydrophobicity, but, while increasing hydrophobicity makes stronger inhibitors of the enzyme in vitro, it can diminish the effectiveness in vivo by decreasing permeability through the cell membrane. A structure-activity analysis of published Ki's for pyrazoles acting against human pi-ADH indicates that its active site differs from those in other alcohol dehydrogenases.     

Recurrent Evolution of Melanism in South American Felids

Morphological variation in natural populations is a genomic test bed for studying the interface between molecular evolution and population genetics, but some of the most interesting questions involve non-model organisms that lack well annotated reference genomes. Many felid species exhibit polymorphism for melanism but the relative roles played by genetic drift, natural selection, and interspecies hybridization remain uncertain. We identify mutations of Agouti signaling protein (ASIP) or the Melanocortin 1 receptor (MC1R) as independent causes of melanism in three closely related South American species: the pampas cat (Leopardus colocolo), the kodkod (Leopardus guigna), and Geoffroy’s cat (Leopardus geoffroyi). To assess population level variation in the regions surrounding the causative mutations we apply genomic resources from the domestic cat to carry out clone-based capture and targeted resequencing of 299 kb and 251 kb segments that contain ASIP and MC1R, respectively, from 54 individuals (13–21 per species), achieving enrichment of ~500–2500-fold and ~150x coverage. Our analysis points to unique evolutionary histories for each of the three species, with a strong selective sweep in the pampas cat, a distinctive but short melanism-specific haplotype in the Geoffroy’s cat, and reduced nucleotide diversity for both ancestral and melanism-bearing chromosomes in the kodkod. These results reveal an important role for natural selection in a trait of longstanding interest to ecologists, geneticists, and the lay community, and provide a platform for comparative studies of morphological variation in other natural populations.