No abstract

Mutant AT268 of Azotobacter vinelandii - showing diminished production of poly-beta-hydroxybutyrate (PHB) due to a mutation in phbR (the gene coding for the transcriptional activator of the phbBAC biosynthetic operon); mutant CNT26, containing a mutation (muc26) that increases the transcription of gene algD (encoding GDP mannose dehydrogenase, the key enzyme in alginate biosynthesis); and mutant DM, carrying both phbR and muc26 mutations - were characterised in terms of alginate production, broth viscosity, and molecular weight of the alginate. All the mutants evaluated produced 25% less alginate with respect to that produced by the wild type. Unexpectedly and with no apparent relation to the phbR and muc26 mutations, mutant DM exhibited the highest molecular weight ever reported for a bacterial alginate (up to 4 x 10(6) Da), with a very low polydispersity index (1.3). Acetyl content in the alginate produced by this strain was low (1.4-2.6%). These characteristics make this mutant a very valuable source for producing alginates with improved properties.

We study the dynamics of Newtonian fluids subject to complex pressure gradients within bent oscillating nanotubes. Pressure gradients with four different purely oscillatory time profiles are explored by theoretical means, in order to unveil the mechanism of interaction between the characteristic time of tube vibration and the multiple characteristic times involved in the complex pressure signal. We find out that all the characteristic times of the system are mixed as a consequence of the nonlinear fluid-tube coupling caused by Coriolis force, which is induced by the local nanotube rotation and is distinctive of micro- and nanometric confinements subject to vibration. Our computations predict a vast range of resonances, not only the ones expected when the magnitude of pressure frequency is close to the magnitude of tube frequency, but also resonances where the pressure frequency is considerably lower than the tube frequency. These resonances could be exploited to obtain controllable combined oscillatory and net flow rates, even when the actuator's frequencies cannot reach the tube vibration frequencies. Our findings provide a theoretical framework for future applications in generation of complex oscillatory and net flow rates with a single actuator, using relatively low instrumentation.