Dynamic trapping and two-dimensional transport of swimming microorganisms using a rotating magnetic microrobot

Manipulation of microorganisms with intrinsic motility is a challenging yet important task for many biological and biomedical applications. Currently, such a task has only been accomplished using optical tweezers, while at the risk of averse heating and photodamage of the biological samples. Here, we proposed a new micro-robotic approach for fluidic trapping and two-dimensional transportation of motile microorganisms near a solid surface in fluids. We demonstrated selective trapping and transportation of individual freely swimming multi-flagellated bacteria over a distance of 30 μm (7.5 body length of the carrier) on a surface, using the rotational flows locally induced by a rotating magnetic microparticle. Only a weak uniform magnetic field (<3 mT) was applied to actuate the microparticle. The microparticle can translate on a glass substrate by rotating at a speed of up to 100 μm s(-1), while providing a fluidic force of a few to tens of pico-Newtons.

Mineralization of chlorpyrifos by co-culture of Serratia and Trichosporon spp

A bacterial strain (Serratia sp.) that could transform chlorpyrifos to 3,5,6-trichloro-2-pyridinol (TCP) and a TCP-mineralizing fungal strain (Trichosporon sp.) were isolated from activated sludge by enrichment culture technique. The fungus could also degrade 50 mg chlorpyrifos l(-1) within 7 days. Co-cultures completely mineralized 50 mg chlorpyrifos l(-1) within 18 h at 30 degrees C and pH 8 using a total inocula of 0.15 g biomass l(-1).

The interaction of thin-film flow, bacterial swarming and cell differentiation in colonies of Serratia liquefaciens

The rate of expansion of bacterial colonies of S. liquefaciens is investigated in terms of a mathematical model that combines biological as well as hydrodynamic processes. The relative importance of cell differentiation and production of an extracellular wetting agent to bacterial swarming is explored using a continuum representation. The model incorporates aspects of thin film flow with variable suspension viscosity, wetting, and cell differentiation. Experimental evidence suggests that the bacterial colony is highly sensitive to its environment and that a variety of mechanisms are exploited in order to proliferate on a variety of surfaces. It is found that a combination of effects are required to reproduce the variation of bacterial colony motility over a large range of nutrient availability and medium hardness.

Serratia liquefaciens swarm cells exhibit enhanced resistance to predation by Tetrahymena sp

Tetrahymena sp. was found to graze extensively on Serratia liquefaciens MG1 swim cells (1.5-3 microns long rods) resulting in the rapid elimination of the bacterial strain. However, when S. liquefaciens cells are exposed to certain surfaces they differentiate into elongated, highly motile swarm cells and these cells were found to be grazing-resistant provided their length exceeded 15 microns.

[Morphological studies on antibacterial activities of cefotiam (author's transl)]

1. Cefotiam was demonstrated to be more potent than cefazolin in its antibacterial activities against clinical isolates of E. coli, Klebsiella, Serratia, Proteus mirabilis, Proteus morganii and Proteus inconstans. MICs of cefotiam with 10(6) cells/ml inoculum size were considerably lower than those with 10(8) cells/ml. 2. Organisms lysed when exposed to cefotiam at concentrations higher than the MICs with 10(8) cells/ml. Morphological changes of organisms into filament occurred even at concentrations lower than the MICs with 10(6) cells/ml. This indicates that cefotiam is incorporated into organisms at remarkably low concentrations and exerts its antibacterial activities. 3. Cefotiam showed a high affinity for penicillin-binding proteins (PBP) 1A, 1Bs and 3. The formation of filament at low concentrations of cefotiam is possibly attributable to the high affinity of cefotiam for PBP 3 in addition to its high permeability through outer cell membrane. 4. As the antibacterial activities of cefotiam are displayed at lower concentrations, it is reasonable to consider that doses of cefotiam on clinical use can be reduced in comparison with those of conventional cephalosporins.