A general method for identification of polyhydroxyalkanoic acid synthase genes from pseudomonads belonging to the rRNA homology group I

Using a 30-mer oligonucleotide probe highly specific for polyhydroxyalkanoic acid (PHA) synthase genes, the respective genes of Pseudomonas citronellolis, P. mendocina, Pseudomonas sp. DSM 1650 and Pseudomonas sp. GP4BH1 were cloned from genomic libraries in the cosmid pHC79. A 19.5-kbp and a 22.0-kbp EcoRI restriction fragment of P. citronellolis or Pseudomonas sp. DSM 1650, respectively, conferred the ability to accumulate PHA of medium-chain-length 3-hydroxyalkanoic acids (HA _mcl ) from octanoate as well as from gluconate to the PHA-negative mutant P. putida GPp104. An 11.0-kbp EcoRI fragment was cloned from P. mendocina, which restored in GPp104 the ability to synthesize PHA from octanoate but not from gluconate. From Pseudomonas sp. GP4BH1 three different genomic fragments encoding PHA synthases were cloned. This indicated that strain GP4BH1 possesses three different functionally active PHA synthases. Two of these fragments (6.4 kbp and 3.8 kbp) encoded for a PHA synthase, preferentially incorporating hydroxyalkanoic acids of short chain length (HA _scl ), and the synthases were expressed in either GPp104 and Alcaligenes eutrophus H16-PHB^–4, respectively. The PHA synthase encoded by the third fragment (6.5 kbp) led to the incorporation of HA _mcl and was expressed in GPp104 but not in PHB^–4. Correspondence to: A. Steinbüchel     

Invasibility as an emergent property of native metapopulation structure

Biological invasions constitute major threats to global biodiversity. Eco‐evolutionary considerations highlight the importance of contemporary evolution in community responses to bioinvasions. However, effects of metapopulation structure on invasion success have been mostly overlooked even though metapopulation structure determines gene flow and is likely to affect evolutionary processes. Here, we investigate a stepping‐stone model with evolving alien native interaction strengths. We demonstrate analytically that the site of invasion can determine the success of an invading consumer because gene flow and demography of a local resource species interact to obstruct local resource adaptation. Our main results are 1) that invasion success is more likely in genetic sink populations of the native species and 2) that invasion is more likely to occur against the migrational flow of native species. These findings suggest that invasibility is best regarded as an emergent property not only of communities but of entire metapopulations. Since migration networks of aliens and natives are often mismatched due to anthropogenic interference, our results indicate how population structure eases the spread of invasives against the migrational flow of natives.     

Observations on the origin of the non-linear van't Hoff behaviour of polypeptides in hydrophobic environments.

In this paper we describe a general procedure to determine the thermodynamic parameters associated with the interaction of polypeptides or proteins with immobilised lipophilic compounds such as non-polar n-octyl groups. To this end, the binding behaviour of an all L-alpha-polypeptide, 1, and its retro-inverso-isomer, 2, has been investigated with an n-octylsilica and water-organic solvent mixture containing different percentages of acetonitrile or methanol over the temperature range of 278-338 K. The results confirm that non-linear van'ts Hoff plots occur with this pair of polypeptide isomers, depending on the solvent composition. These findings are consistent with the changes in the thermodynamic parameters, enthalpy of association, delta Hoassoc,i, entropy of association, delta Soassoc,i, and heat capacity, delta Cop,i, all having significant temperature dependencies. Theoretical relationship linking the changes in the delta Hoassoc,i, delta Soassoc,i and delta Cop,i values of these polypeptide-non-polar ligate systems, as a function of temperature, T, have been validated. Significant differences were observed in the magnitudes of these thermodynamic quantities when acetonitrile or methanol was employed as the organic solvent. The origin of these solvent-dependent effects can be attributed to the hydrogen-bonding propensity of the respective solvent. Involvement of enthalpy-entropy compensation effects associated with the interaction of these polypeptides with the hydrophobic ligates has also been documented. Analysis of empirical extra-thermodynamic relationships associated with molecular structural properties of these polypeptides, such as the slope term, S, derived from the plots of the logarithmic capacity factor, log k'i, of these polypeptides vs. the volume fraction of the organic solvent, [symbol: see text] as a function of temperature, T, has also revealed similar correlations in terms of the interactive behaviour of polypeptides 1 and 2 under these experimental conditions. These findings provide an extended thermodynamic and extra-thermodynamic framework to examine the solvational, conformational and other equilibrium processes that polypeptides (or proteins) can undergo in the presence of n-alkylsilicas or other classes of immobilised hydrophobic surfaces. The experimental approach utilised in this study with these topologically similar polypeptides thus represents a generic procedure to explore the behaviour of polypeptides or proteins in non-polar environments in terms of their molecular properties and the associated linear free energy relationships that determine their interactive behaviour.