Dynamic aspects of the structured cell population in a swarming colony of Proteus mirabilis - PubMed (original) (raw)

Dynamic aspects of the structured cell population in a swarming colony of Proteus mirabilis

T Matsuyama et al. J Bacteriol. 2000 Jan.

Abstract

Proteus mirabilis forms a concentric-ring colony by undergoing periodic swarming. A colony in the process of such synchronized expansion was examined for its internal population structure. In alternating phases, i.e., swarming (active migration) and consolidation (growth without colony perimeter expansion), phase-specific distribution of cells differing in length, in situ mobility, and migration ability on an agar medium were recognized. In the consolidation phase, the distribution of mobile cells was restricted to the inner part of a new ring and a previous terrace. Cells composing the outer part of the ring were immobile in spite of their ordinary swimming ability in a viscous solution. A sectorial cell population having such an internal structure was replica printed on fresh agar medium. After printing, a transplant which was in the swarming phase continued its ongoing swarming while a transplanted consolidation front continued its scheduled consolidation. This shows that cessation of migration during the consolidation phase was not due to substances present in the underlying agar medium. The ongoing swarming schedule was modifiable by separative cutting of the swarming front or disruption of the ring pattern by random mixing of the pattern-forming cell population. The structured cell population seemed to play a role in characteristic colony growth. However, separation of a narrow consolidation front from a backward area did not induce disturbance in the ongoing swarming schedule. Thus, cells at the frontal part of consolidation area were independent of the internal cell population and destined to exert consolidation and swarming with the ongoing ordinary schedule.

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Figures

FIG. 1

Length of cells making up distinctive areas of a P. mirabilis colony. (A) Cells taken from the designated areas (marked a, b, c, d, e, f, and g) in an actively swarming colony were examined for cell length (more than 100 cells per area). Cell length was graded into four classes. (B) The percentages of cells shorter than 2 μm (black bars), 2 to 5 μm (hatched bars), 5 to 10 μm (dotted bars), and longer than 10 μm (white bars) at each area are shown.

FIG. 2

Temporal change in the length of cells at the fixed zone of a swarming colony. (A) When a migration front passed the y point, cell length measurement (more than 100 cells) of the y zone started (0 h time). After the migration front passed the z zone and consolidation started (2 h time), cell length measurement of the z zone started. Just after the next swarming period started, the last measurement (5-h time) was undertaken. (B) Temporal cell length changes at the y zone. (C) Temporal cell length changes at the z zone. The percentages of cells shorter than 2 μm (black bars), 2 to 5 μm (hatched bars), 5 to 10 μm (dotted bars), and longer than 10 μm (white bars) at each time point are shown.

FIG. 3

Swimming activity of cells from representative areas (the center of the colony, swarming band, and consolidation band) of a swarming colony. The cell length and swimming velocity (in 2% PVP solution) of each cell are shown.

FIG. 4

Swimming activity of cells entering into the consolidation phase. The length (A) and swimming velocity (B) of cells taken at the indicated time from the front area, which was full of nontranslocating cells, are shown. Cells were suspended in 2% PVP solution. Vertical error bars denote SD (n = 20).

FIG. 5

Swimming swarmer cell with a bundle of rotating flagella. Cells taken from the consolidation area were suspended in 5% PVP. Swarmer cells were swimming straight and independently without making an interactive cell group. Some cells made a folded helix form, as shown here. To visualize flagella in a photograph, a cell with slowly rotating flagella (arrowhead) was photographed with Fuji PROVIA (ASA 1600) film. Bar, 5 μm.

FIG. 6

In situ mobile activities of cells at the front of and inside a P. mirabilis colony. A front area (A) and an area just behind the front (B) at the beginning of consolidation, a 1-mm inside front area (C), a backward area near to the latest terrace (D), and the latest terrace area (E) at the early consolidation phase, and a margin of a newly formed terrace (F) at the beginning of swarming were directly examined under a phase-contrast microscope. All micrographs were taken at a 1-s exposure to discriminate moving cells (blurred images as partly indicated by arrows) from nonmoving cells. T, silent cell mass forming a terrace. Bar, 20 μm.

FIG. 7

Modification of the swarming schedule by disorganization of the structured cell population. Upper sector, early ending of swarming phase after separation (C indicates the cut line) from the latest terrace. Lower sector, extended migration canceling the scheduled consolidation period after random mixing (marked with M) of the sectorial cell population. The stars indicate the growing edge of part of the untreated colony. The photograph was taken 200 min after cutting and 60 min after mixing.

FIG. 8

Behavior of a replica-printed cell population. The sectorial part of a colony at the early swarming phase (A) and the early consolidation phase (B) was replica-printed onto fresh agar medium. A thin cell population is migrating from the printed swarming front, lateral cut ends near the front, and lateral cut ends near the latest terrace. There is no cell migration from the consolidation front at this stage. Photographs were taken 60 min after replica-printing. Short lines indicate the original front of the printed cell population.

FIG. 9

Anisotropic swarming from a printed ring band area. At the early consolidation phase, a trapezoidal area with a newly formed ring band was excised and replica-printed onto fresh agar medium. Cell migration from the shorter edge (small arrowhead, inner boundary of the ring band) began immediately. Cell migration from the longer edge (large arrowhead, consolidation front of the band) began at the expected consolidation-ending time. Rings differing in phases developed without entrainment. A replica-printed agar plate was incubated for 23 h. Formation of terraces with microcolonies (lines of dark dots along the terrace edge) is recognizable, except for the shorter edge of the printed cell population.

FIG. 10

Effects of azimuthal and radial cuts of a swarming colony. At the beginning stage of the second consolidation, a colony was divided into four parts by radial cuts, and then a thin front cell film on one of one-eighth sectors was separated from the rear area by an azimuthal cut. (A) A divided colony. a, sector with an azimuthal cut; b, sector without an azimuthal cut; c, semicircular part of a colony. (B) Expansion time course of the divided colony edges. Each point indicates a mean of 10 experiments. SD values were less than 3.6%. Solid circle, radius before cutting; open square, radius of a; open triangle, radius of b; open circle, radius of c. Differences in radius measurement were significant between a and b (P < 0.05 at 16.5 and 21.0 h postinoculation) and b and c (P < 0.01 at 16.5 and 21.0 h postinoculation).

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Dynamic aspects of the structured cell population in a swarming colony of Proteus mirabilis - PubMed (original) (raw)