Bacterial swimming strategies and turbulence

Most bacteria in the ocean can be motile. Chemotaxis allows bacteria to detect nutrient gradients, and hence motility is believed to serve as a method of approaching sources of food. This picture is well established in a stagnant environment. In the ocean a shear microenvironment is associated with turbulence. This shear flow prevents clustering of bacteria around local nutrient sources if they swim in the commonly assumed "run-and-tumble" strategy. Recent observations, however, indicate a "back-and-forth" swimming behavior for marine bacteria. In a theoretical study we compare the two bacterial swimming strategies in a realistic ocean environment. The "back-and-forth" strategy is found to enable the bacteria to stay close to a nutrient source even under high shear. Furthermore, rotational diffusion driven by thermal noise can significantly enhance the efficiency of this strategy. The superiority of the "back-and-forth" strategy suggests that bacterial motility has a control function rather than an approach function under turbulent conditions.     

The question of uniqueness of ancient bacteria

Microorganisms are associated with a variety of ancient geological materials. However, conclusive proof that these organisms are as old as the geological material and not more recent introductions has generally been lacking. Over the years, numerous reports of the isolation of ancient bacteria from geological materials have appeared. Most of these have suffered from the fact that the protocol for the surface sterilization of the sample was either poorly defined, inadequate or rarely included data to validate the overall effectiveness of the sterilization protocol. With proper sterility validation and isolation protocol, a legitimate claim for the isolation of an ancient microbe can be made. Biochemical, physiological, or morphological data indicate that these ancient microbes are not significantly different from modern isolates. As the role (decomposition) of modern and ancient microbes has not changed over time, it is probably unreasonable to expect these organisms to be vastly different. A discussion on the reasons for the homogeneity of ancient and modern microbes is presented. Journal of Industrial Microbiology & Biotechnology (2002) 28, 32–41 DOI: 10.1038/sj/jim/7000174 Received 20 May 2001/ Accepted in revised form 16 June 2001     

The effects of azadirachtin-treated diets on the feeding behaviour and fecundity of the peach-potato aphid,Myzus persicae

Adult apterousMyzus persicae, which had fed for 26 h on diet containing azadirachtin at concentrations of 25–100 ppm, produced nymphs at less than half the rate of aphids on control diets. After 50 h on azadirachtin-treated diets nymph production had virtually ceased. After this period, any nymphs produced by adults that had fed on azadirachtin-treated diets were born dead with undeveloped appendages. Honeydew production on azadirachtin-treated diets was unaffected during the first 26 h period but was approximately three times less than on control diets during the subsequent 24 h period.     

Human immunodeficiency virus type 1 vectors with alphavirus envelope glycoproteins produced from stable packaging cells

Alphavirus glycoproteins have broad host ranges. Human immunodeficiency virus type 1 (HIV-1) vectors pseudotyped with their glycoproteins could extend the range of tissues that can be transduced in both humans and animal models. Here, we established stable producer cell lines for HIV vectors pseudotyped with alphavirus Ross River virus (RRV) and Semliki Forest virus (SFV) glycoproteins E2E1. RRV E2E1-stable clones could routinely produce high-titer pseudotyped vectors for at least 5 months. SFV E2E1-stable clones, however, produced relatively low titers. We examined the properties of RRV E2E1-pseudotyped vectors [HIV-1(RRV)] and compared them with amphotropic murine leukemia virus Env- and vesicular stomatitis virus glycoprotein G-pseudotyped vectors. HIV-1(RRV) displayed a number of characteristics which would be advantageous in ex vivo and in vivo experiments, including resistance to inactivation by heat-labile components in fresh human sera and thermostability at 37 degrees C. Upon single-step concentration by ultracentrifugation of HIV-1(RRV), we could achieve vector stocks with titers up to 6 x 10(7) IU/ml. HIV-1(RRV) efficiently transduced cells from several different species, including murine primary dendritic cells, but failed to transduce human and murine T cells as well as human hematopoietic stem cells (HSC). These results indicate that HIV-1(RRV) could be used in a number of applications including animal model experiments and suggest that expression of RRV cellular receptors is limited or absent in certain cell types such as T cells and human HSC.     

Functionally active t1-t1 interfaces revealed by the accessibility of intracellular thiolate groups in kv4 channels

Gating of voltage-dependent K(+) channels involves movements of membrane-spanning regions that control the opening of the pore. Much less is known, however, about the contributions of large intracellular channel domains to the conformational changes that underlie gating. Here, we investigated the functional role of intracellular regions in Kv4 channels by probing relevant cysteines with thiol-specific reagents. We find that reagent application to the intracellular side of inside-out patches results in time-dependent irreversible inhibition of Kv4.1 and Kv4.3 currents. In the absence or presence of Kv4-specific auxiliary subunits, mutational and electrophysiological analyses showed that none of the 14 intracellular cysteines is essential for channel gating. C110, C131, and C132 in the intersubunit interface of the tetramerization domain (T1) are targets responsible for the irreversible inhibition by a methanethiosulfonate derivative (MTSET). This result is surprising because structural studies of Kv4-T1 crystals predicted protection of the targeted thiolate groups by constitutive high-affinity Zn(2+) coordination. Also, added Zn(2+) or a potent Zn(2+) chelator (TPEN) does not significantly modulate the accessibility of MTSET to C110, C131, or C132; and furthermore, when the three critical cysteines remained as possible targets, the MTSET modification rate of the activated state is approximately 200-fold faster than that of the resting state. Biochemical experiments confirmed the chemical modification of the intact alpha-subunit and the purified tetrameric T1 domain by MTS reagents. These results conclusively demonstrate that the T1--T1 interface of Kv4 channels is functionally active and dynamic, and that critical reactive thiolate groups in this interface may not be protected by Zn(2+) binding.     

Induction of Bacillus brevis L-forms

L-forms of Bacillus brevis were induced and maintained in L-phase medium supplemented with inactivated horse serum with a combination of penicillin (80 u/ml) and cephalosporin (5 μg/ml) in liquid medium and penicillin (200 u/ml) in diphasic culture. These L-forms failed to grow on solid media.