The 3D architecture of a bacterial swarm has implications for antibiotic tolerance.

Swarming bacteria are an example of a complex, active biological system, where high cell density and super-diffusive cell mobility confer survival advantages to the group as a whole. Previous studies on the dynamics of the swarm have been limited to easily observable regions at the advancing edge of the swarm where cells are restricted to a plane. In this study, using defocused epifluorescence video imaging, we have tracked the motion of fluorescently labeled individuals within the interior of a densely packed three-dimensional (3D) region of a swarm. Our analysis reveals a novel 3D architecture, where bacteria are constrained by inter-particle interactions, sandwiched between two distinct boundary conditions. We find that secreted biosurfactants keep bacteria away from the swarm-air upper boundary, and added antibiotics at the lower swarm-surface boundary lead to their migration away from this boundary. Formation of the antibiotic-avoidance zone is dependent on a functional chemotaxis signaling system, in the absence of which the swarm loses its high tolerance to the antibiotics.

Overproduction of individual gas vesicle proteins perturbs flotation, antibiotic production and cell division in the enterobacterium Serratia sp. ATCC 39006.

Gas vesicles are intracellular proteinaceous organelles that facilitate bacterial colonization of static water columns. In the enterobacterium Serratia sp. ATCC 39006, gas vesicle formation requires the proteins GvpA1, GvpF1, GvpG, GvpA2, GvpK, GvpA3, GvpF2 and GvpF3 and the three gas vesicle regulatory proteins GvrA, GvrB and GvrC. Deletion of gvpC alters gas vesicle robustness and deletion of gvpN or gvpV results in small bicone vesicles. In this work, we assessed the impacts on gas vesicle formation when each of these 14 essential proteins was overexpressed. Overproduction of GvpF1, GvpF2, GvrA, GvrB or GvrC all resulted in significantly reduced gas vesicle synthesis. Perturbations in gas vesicle formation were also observed when GvpV and GvpA3 were in excess. In addition to impacts on gas vesicle formation, overproduction of GvrA or GvrB led to elevated biosynthesis of the tripyrrole pigment, prodigiosin, a secondary metabolite of increasing medical interest due to its antimalarial and anticancer properties. Finally, when GvpG was overexpressed, gas vesicles were still produced, but the cells exhibited a growth defect. Further analysis showed that induction of GvpG arrested cell growth and caused a drop in viable count, suggesting a possible physiological role for this protein linking gas vesicle biogenesis and binary fission. These combined results demonstrate that the stoichiometry of individual gas vesicle proteins is crucially important for controlled organelle morphogenesis and flotation and provides evidence for the first link between gas vesicle assembly and cell division, to our knowledge.

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.

Using non-invasive magnetic resonance imaging (MRI) to assess the reduction of Cr(VI) using a biofilm-palladium catalyst.

Industrial waste streams may contain contaminants that are valuable like Pd(II) and/or toxic and mutagenic like Cr(VI). Using Serratia sp. biofilm the former was biomineralized to produce a supported nanocrystalline Pd(0) catalyst, and this biofilm-Pd heterogeneous catalyst was then used to reduce Cr(VI) to less dangerous Cr(III) at room temperature, with formate as the electron donor. Cr(VI)((aq)) is non-paramagnetic while Cr(III)((aq)) is paramagnetic, which enabled spatial mapping of Cr species concentrations within the reactor cell using non-invasive magnetic resonance (MR) imaging experiments. Spatial reactivity heterogeneities were thus examined. In batch reactions, these could be attributed primarily to heterogeneity of Pd(0) distribution and to the development of gas bubbles within the reactor. In continuous flow reactions, spatial reactivity heterogeneities resulted primarily from heterogeneity of Cr(VI) delivery.

Colonización por Serratia fonticola de una úlcera vascular venosa en el miembro inferior izquierdo / Colonization by Serratia fonticola of vascular-venous ulcer in lower left limb

Presentamos el caso de una paciente afectada de insuficiencia vascular venosa periférica derivada desde la consulta de enfermería por padecer una úlcera vascular de meses de evolución. Se realiza un cultivo del exudado de dicha úlcera, que muestra una colonización por la enterobacteria Serratia fonticola. Al tratar esta infección con ciprofloxacino, la paciente evoluciona favorablemente; al cabo de tres meses la úlcera se ha curado dejando una cicatriz queloidea (AU)

We present the case of a female patient with peripheral venous and vascular insufficiency, referred from the nursing consultation due to a vascular ulcer of several months’ evolution. Exudate was collected and a culture made, with the finding of colonization by the enterobacterium Serratia fonticola. This infection was treated with ciprofloxacin, its evolution being favorable. The patient was cured after three months, a queloid scar remaining (AU)

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.