Swarming behavior of a novel strain of Brevibacillus thermoruber

Abstract

Brevibacillus thermoruber strain Nabari was isolated from compost and identified based on 16 S rRNA gene sequencing and DNA-DNA hybridization using B. thermoruber DSM 7064 T as the standard, despite some differences in their physiological and structural characteristics. When B. thermoruber Nabari was cultivated on various solid media containing 1.5% agar at 60°C, it rapidly propagated over the entire plate. In particular, on R2A-agar medium, it formed fine dendritic colonies. Macroscopic and microscopic observations of peripheral regions of the colonies indicated that the dendritic patterns were formed by bacterial swarming of some of the cells; large flows of bacterial cell populations were observed in the peripheral regions of the dendritic colonies. The cells were highly flagellated, but no extreme elongation of cells was observed. When B. thermoruber Nabari cells were cultivated at 37°C on R2Aagar plates, most colonies were nonmotile, but some colonies were motile. For example, a wandering colony moved on the plate and split into two, and then they collided to become one again. Additionally, a simple incubation system was devised to record the movement of colonies at high temperatures in this study while protecting the cameras from thermal damage.

Unique behavioral patterns of wandering colonies of Brevibacillus thermoruber on agar plates

“…In our preceding study [19], we found that B. thermoruber Nabari produced motile colonies when cultivated on R2A‐agar plates at 37°C. However, because B. thermoruber Nabari is a thermophilic bacterium with an optimal growth temperature of about 55°C, it takes a long time for us to observe its growth and colony movement on agar plates at 37°C.…”

“…2.1 | Bacterial strain and culture conditions B. thermoruber strain Nabari, isolated from compost in Nabari, Japan, was used [19]. R2A Broth "DAIGO" was purchased from Fujifilm Wako Pure Chemical Co. and BA-10 agar from Funakoshi Co., Ltd. 2 × R2A medium contained twice the concentration of the components of regular R2A medium.…”

“…B. thermoruber Nabari cells from a single colony were streaked in zigzags on R2A or 2×R2A-agar plates in the absence or presence of Tween 20 and incubated at 37°C [19]. Alternatively, a liquid culture of the bacterium at 50°C was diluted to ca.…”

“…In our previous paper, we reported that Brevibacillus thermoruber strain Nabari, isolated from compost, produced dendritic colonies when cultured on an reasoner's 2A agar (R2A-agar) medium at 55°C and motile colonies when cultured at 37°C [19]. We are interested in motile colonies rather than pattern formation by swarming because the latter phenomenon has already been studied intensively [4,5].…”