Adaptation of Pseudomonas sp. GJ1 to 2-bromoethanol caused by overexpression of an NAD-dependent aldehyde dehydrogenase with low affinity for halogenated aldehydes

Pseudomonas sp. GJ1 is able to grow with 2-chloroethanol as the sole carbon and energy source, but not with 2-bromoethanol, which is toxic at low concentrations (1 mM). A muatnt that could grow on 2-bromoethanol with a growth rate of 0.034 h^–1 at concentrations up to 5 mM was isolated and designated strain GJ1M9. Measurement of enzyme activities showed that mutant and wild-type strains contained a PMS-linked alcohol dehydrogenase that was active with halogenated alcohols and that was threefold overexpressed in the mutant when grown on 2-chloroethanol, but only slightly overproduced when grown on 2-bromoethanol. Both strains also contained an NAD-dependent alcohol dehydrogenase that had no activity with halogenated alcohols. Haloacetate dehalogenase levels were similar in the wild-type and the mutant. Activities of NAD-dependent aldehyde dehydrogenase were only slightly higher in extracts of the mutant grown with 2-bromoethanol than in those of the wild-type grown with 2-chloroethanol. SDS-PAGE, however, showed that this enzyme amounted to more than 50% of the total cellular protein in extracts of the mutant from 2-bromoethanol-grown cells, which was fourfold higher than in extracts of the wild-type strain grown on 2-chloroethanol. The enzyme was purified and shown to be a tetrameric protein consisting of subunits of 55 kDa. The enzyme had low K_m values for acetaldehyde and other non-halogenated aldehydes (0.8–4 μM), but much higher K_m values for chloroacetaldehyde (1.7 mM) and bromoacetaldehyde (10.5 mM), while V_max values were similar for halogenated and non-halogenated aldehydes. Cultures that were pregrown on 2-chloroethanol rapidly lost aldehyde dehydrogenase activity after addition of 2-bromoethanol and chloroamphenicol, which indicates that bromoacetaldehyde inactivates the enzyme. To achieve growth with 2-bromoethanol, the high expression of the enzyme thus appears to be necessary in order to compensate for the high K_m for bromoacetaldehyde and for inactivation of the enzyme by bromoacetaldehyde. Received: 31 August 1995 / Accepted: 4 December 1995     

Larval selection of substrate by the Bryozoa discoporella and Cupuladria

Summary The mineralogy, shape, and size distribution of sand grains which form the nucleus for colonial growth in Discoporella umbellata depressa and Cupuladria doma have been examined and compared to these same parameters in the sediment from which the species were collected. These bryozoa, occurring on the continental shelf of Georgia, encrust sand grains. The diameters of the encrusted grains greatly exceed the mean diameter of particles in the associated sediment. D. umbellata depressa encrusts larger grains than does C. doma. Encrusted grains are composed of quartz and rock fragments. No zoaria of either species were found that had encrusted carbonate grains despite the fact that such grains form an important fraction of the sediment in the study area. Larval selection of fixation sites on the basis of grain size and mineralogy is suggested. It is further suggested that these sedimentary parameters may partially explain the fact that both bryozoan species are abundantly present on the continental shelf of the southeastern United States but are nearly absent from the continental slope.

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Résumé La minéralogy, la configuration et le classement par ordre de grandeur des grains de sable qui forment le centre pour le grandissement colonial dans Discoporella umbellata depressa et Cupuladria doma ont été examinés et comparés à ces mêmes paramèters dans les alluvionnements d'où venaient les especès mentionnées. Ces bryozoaires, qui se trouvent sur le banc continental de Georgie encro?tent des grains de sable. Les diamèters des grains encro?tés dépassent de beaucoup le diametre moyen des particules dans les alluvionnements associés. D. umbellata depressa encro?te de plus grands grains que C. doma. Les grains encro?tés se composent de quartz et de fragments de rocker. On n'a trouvé aucun zoaria des deux especes qui avait encroute des grains de carbonate, malgré le fait que de tels grains font une importante fraction de l'alluvionnement dans Faire de notre spécialization. On suggère un choix larvaire des sites de fixation, basé sur la grandeur des grains et la minéralogy. De plus, on suggerè que ces parametrès sédimentaires pourraient expliquer en partie le fait que tous les deux espèces bryozoaires sont présentes en grand nombre sur le bane continental du sud-est des Etats-Unis, mais sont à peu près absentes du talus continental.