Growth-induced mass flows in fungal networks

Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks.     

Regulation of enterochelin synthetase in Escherichia coli K-12

Enterochelin synthetase activity is controlled by both repression and feed-back inhibition mechanisms. Inclusion of iron in growth media results in synthesis of all four (D, E, F and G) components of enterochelin synthetase being repressed. The specific inhibition of L-serine activation (partial reaction catalyzed by the F component) by the end products, ferric-enterochelin and 2,3-dihydroxybenzoylserine, is shown to inhibit overall enterochelin synthetase activity.     

Molecular genetic organization and origin of plasmid pBS52 with a broad range of bacterial hosts

The data are presented on the localization of genetic determinants of resistance to streptomycin, ampicillin and sulfanilamides on the physical map of conjugative R plasmid pBS52 of 38,000 bp which has a broad bacterial host range and belongs to a new incompatibility group. The plasmid has a natural "polylinker" site (less than 200 bp) containing (in the order of arrangement) the recognition sites for restriction enzymes: BamHI-EcoRI-PstI-EcoRV-BglII (PvuII). The comparative analysis shows that pBS52 contains a segment homologous to DNA of plasmid RSE1010 (IncP-4). The evolutionary origin of plasmid pBS52 is discussed. The recA-independent formation of the mini-derivatives of pBS373 and pBS374 types during the transformation of Escherichia coli with pBS52 plasmid DNA has been shown. Plasmids pBS373 and yBS374 are capable of autonomous replication in Pseudomonas putida and P. aeruginosa cells, which is provided by the rep system of IncP-4 replicon.