Functional analysis of putative transporters involved in oligotrophic growth of Rhodococcus erythropolis N9T-4.

Rhodococcus erythropolis N9T-4, which is an extremely oligotrophic bacterium, can survive in a completely inorganic medium with no additional carbon source. This bacterium utilizes atmospheric CO2, but does not require any additional energy source such as light and hydrogen gas, required by autotrophic microorganisms. However, its CO2 fixation and energy-acquisition systems in the oligotrophic growth remain unrevealed. We expected N9T-4 to have the transporter(s) that imports essential compound(s) for its oligotrophic growth. Three putative ATP-binding cassette (ABC) transporters were found to be highly upregulated under oligotrophic conditions. We constructed the gene-deletion mutants of a gene encoding the substrate-binding protein for each ABC transporter (∆sbp1, ∆sbp2, and ∆sbp3). Among these mutants, ∆sbp1 showed growth defects on oligotrophic medium without carbon source. We examined the growth of the mutants on the oligotrophic medium containing 1% trehalose as a sole carbon source. The results exhibited worse growth of ∆sbp3 than that of the control strain (∆ligD), whereas intracellular trehalose content of all mutants decreased compared with that of ∆ligD. It was reported that trehalose functions as the mycolate carrier to the arabinogalactan layer in the cell wall of Mycobacterium tuberculosis. Transmission electron microscopic analysis of ∆sbp1 cells showed that an outermost envelope of the ∆sbp1 cell diminished, which was expected to be mycolate layer. From these results, we suggest that the same trehalose-recycling system as that in a Mycobacterium cell functions in the oligotrophic growth of N9T-4, and the ABC transporter comprising Sbp1 as the substrate-binding protein is strongly involved in the oligotrophic growth of N9T-4.

Establishment of an effective oligotrophic cultivation system for Rhodococcus erythropolis N9T-4.

Rhodococcus erythropolis N9T-4 grows on an inorganic solid-state medium with no additional carbon and energy sources; however, it is unable to grow well in a liquid culture medium under the oligotrophic conditions. We examined submerged cultivations of N9T-4 using a polyurethane foam sponge to achieve approximately 10 times of the oligotrophic growth of the bacterium in the liquid culture medium.

The impact of adenosine pharmacologic stress combined with low-level exercise in patients undergoing myocardial perfusion imaging (BIWAKO adenosine-Ex trial).

BACKGROUND: The combination of adenosine infusion with low-level exercise has become a common approach for inducing stress during stress myocardial perfusion imaging (MPI). We investigated stress MPI performed by combined low-level exercise and adenosine infusion. This combined protocol can decrease adverse reactions and reduce the effect of scattered rays from the liver. METHODS AND RESULTS: Subjects were clinically referred for a 53-min rest-stress Tc-99m Sestamibi MPI procedure using BIWAKO PROTOCOL. Ninety-eight patients (44.5%) underwent adenosine infusion with ergometer exercise testing and 122 patients (55.5%) underwent adenosine infusion without exercise testing. We evaluated the liver/heart (L/H) uptake ratio, background activity in the upper mediastinum, and adverse reactions. RESULTS: The L/H ratio and background activity were lower in the adenosine-exercise group than in the adenosine-non-exercise group (1.8 ± 0.54 vs. 2.1 ± 0.62, P < 0.0056; 43.1 ± 12.2 vs. 61.5 ± 15.4, P < 0.0001). The adenosine-exercise group had fewer adverse reactions than the adenosine-non-exercise group (11.2 vs. 19.7%). All of the adverse reactions were minor, with the exception of severe back pain in one case. The incidence of adverse reactions in our study was lower than that in previous studies for unknown reason. CONCLUSION: Adenosine infusion in combination with low-level exercise seems to result in higher-quality images and fewer adverse reactions than adenosine infusion without exercise. The combined protocol decreases adverse reactions and improves the quality of myocardial perfusion images by decreasing background activity.

Simulation of C. elegans thermotactic behavior in a linear thermal gradient using a simple phenomenological motility model.

The nematode Caenorhabditis elegans has been reported to exhibit thermotaxis, a sophisticated behavioral response to temperature. However, there appears to be some inconsistency among previous reports. The results of population-level thermotaxis investigations suggest that C. elegans can navigate to the region of its cultivation temperature from nearby regions of higher or lower temperature. However, individual C. elegans nematodes appear to show only cryophilic tendencies above their cultivation temperature. A Monte-Carlo style simulation using a simple individual model of C. elegans provides insight into clarifying apparent inconsistencies among previous findings. The simulation using the thermotaxis model that includes the cryophilic tendencies, isothermal tracking and thermal adaptation was conducted. As a result of the random walk property of locomotion of C. elegans, only cryophilic tendencies above the cultivation temperature result in population-level thermophilic tendencies. Isothermal tracking, a period of active pursuit of an isotherm around regions of temperature near prior cultivation temperature, can strengthen the tendencies of these worms to gather around near-cultivation-temperature regions. A statistical index, the thermotaxis (TTX) L-skewness, was introduced and was useful in analyzing the population-level thermotaxis of model worms.