Low-temperature growth of Shewanella oneidensis MR-1

Abstract

Shewanella oneidensis MR-1 is a mesophilic bacterium with a maximum growth temperature of approximately 35 degrees C but the ability to grow over a wide range of temperatures, including temperatures near zero. At room temperature ( approximately 22 degrees C) MR-1 grows with a doubling time of about 40 min, but when moved from 22 degrees C to 3 degrees C, MR-1 cells display a very long lag phase of more than 100 h followed by very slow growth, with a doubling time of approximately 67 h. In comparison to cells grown at 22 degrees C, the cold-grown cells formed long, motile filaments, showed many spheroplast-like structures, produced an array of proteins not seen at higher temperature, and synthesized a different pattern of cellular lipids. Frequent pilus-like structures were observed during the transition from 3 to 22 degrees C.

FIG. 1.

Size variability of S. oneidensis MR-1 grown at 3°C and at 22°C measured from transmission electron microscopy images.

FIG. 2.

Transmission electron microscopy image showing frequent pilus-like intercellular connections among cells of S. oneidensis MR-1 during the transition from growth at 3°C to 22°C.

FIG. 3.

Ultrastructure of S. oneidensis MR-1 growing exponentially at two different temperatures (3°C and 22°C) observed by transmission electron microscopy. Most filaments in the image at 3°C are sectioned transversally (Tr). Two filamentous cells are shown (Fl). About 50% of the filaments at 3°C show large vesicles that are similar to spheroplasts (Sp).

FIG. 4.

Cell morphology of S. oneidensis MR-1 grown at two different temperatures (3°C and 22°C), observed by epifluorescent microscopy (×1,000) after staining with acridine orange.

FIG. 5.

Ultrastructure of S. oneidensis MR-1 growing exponentially at 3°C observed by transmission electron microscopy. Two filamentous cells are shown (Fl), one of them with a spheroplast-like structure attached (Sp).