Effect of low temperatures on growth, structure, and metabolism of Campylobacter coli SP10

Abstract

The effect of low temperatures on the survival, structure, and metabolism of Campylobacter coli SP10, a virulent strain, was investigated. C. coli became nonculturable rapidly at 20 and 10 degree C and slightly later at 4 degrees C. Incubation in a microaerobic atmosphere improved survival, but after day 8, campylobacters were detectable by direct-count procedures only. The increase in the number of coccoid cells was most pronounced at 37 degrees C but also was noticeable at 20 and 10 degrees C. Two forms of coccoid cells were seen electron microscopically, but only one (20 and 10 degrees C) seemed to be a degenerative form. The flagella were shorter at 20 and 10 degrees C, a result which correlates well with the observed slight changes in the 62-kDa protein band. The fatty acid composition of bacterial cells was influenced significantly by low temperatures. An increase in the short-chain and unsaturated acids was noted; above all, a drastic increase in C19:0 cyc at 20 degrees C with a concomitant decrease in C18:1 trans9,cis11 was seen. The concentrations of excreted metabolites were analyzed to obtain information on metabolic activity. Depending on the magnitude of the temperature downshift, the production of organic acids decreased, but it was always observable after a temperature-specific lag phase and regardless of ability to be cultured. Under optimal conditions, succinate, lactate, and acetate were the main metabolites, other acids being of less importance. The pattern changed significantly at lower temperatures. Succinate was never detected at 20 degrees C and was only occasionally detected at 10 and 4 degrees C. At the same time, fumarate concentrations, which are normally not detectable at 37 degrees C, were highest at 20 degrees C and reduced at 10 and 4 degrees C. Inactivation of fumarate reductase was considered to be a possible explanation.

FIG. 1

Survival of C. coli SP10 at different incubation temperatures without gaseous interchange. ——, 37°C; —–—–, 20°C; –··–, 10°C, ––––, 4°C. Asterisks indicate log colony-forming units per milliliter (37°C) after 51 and 148 days.

FIG. 2

C. coli SP10 degenerative coccoid forms. Incubation was done at 20°C for 72 h. Bar, 0.5 μm.

FIG. 3

C. coli SP10 dense coccoid form with long flagellum. Incubation was done at 4°C for 48 h. Bar, 0.5 μm.

FIG. 4

C. coli SP10 with shortened flagellum (arrow). Incubation was done at 20°C after 48 h. Bar, 1 μm.

FIG. 5

Percentages of C_19:0cycl in C. coli SP10 cultures at different incubation temperatures. Lines are as defined in the legend to Fig. 1.

FIG. 6

Ratio of shorter- to longer-chain fatty acids (C_16:x/C_18:x) in C. coli SP10 cultures at different incubation temperatures. Lines are as defined in the legend to Fig. 1.

FIG. 7

Production of fumarate at different incubation temperatures. Symbols: ▪, 20°C; ▧, 10°C; ▩, 4°C. At 37°C, fumarate was not detectable.