Research ArticleNEUROSCIENCE

A circadian clock in a nonphotosynthetic prokaryote

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Science Advances  08 Jan 2021:
Vol. 7, no. 2, eabe2086
DOI: 10.1126/sciadv.abe2086
  • Fig. 1 Entrainment by light and a free-running rhythm in B. subtilis.

    Bioluminescence of PytvA::lux (A) and PkinC::lux (D) under 5 days of entrainment with cycles of darkness and blue light (12-hour D/12-hour L) and after release to constant darkness conditions [DD; (B) and (E)] for 5 days. The temperature was kept constant at 25.5°C. The detrended data are presented as means ± SD. The shading in (A) and (D) shows the timing of the LD cycle (yellow, light phase; gray, dark phase) relative to the bioluminescence. The horizontal bar in (B) and (E) (lower left) shows the time window of 48 hours selected for the analysis of period length. The calculated period length is plotted in (C) and (F); individual data points [(C), N = 16; (F), N = 7] are shown along with the median and interquartile range. See also table S1.

  • Fig. 2 Free-running rhythms in B. subtilis following entrainment in temperature cycles.

    Bioluminescence of PytvA::lux in constant darkness at 25.5°C following 5 days of entrainment in temperature cycles (CW indicates the cold/warm cycle of 12 hours at 25.5°C/12 hours at 28.5°C) is shown. A free-running rhythm is observed in nutrient sporulation medium (NSMP) lacking glucose (A). The detrended data are plotted as means ± SD. The calculated period length of PytvA::lux expression shown in (A) is plotted in (B), where individual data points (N = 8) are shown along with the median and interquartile range. No free-running rhythm is observed in NSMP medium containing glycerol (N = 40) (C) or glucose (N = 15) (D) as a carbon source. See also table S1.

  • Fig. 3 Circadian rhythms in B. subtilis are temperature compensated.

    Bioluminescence of PytvA::lux under constant conditions [22.5°C, N = 25 (A); 25.5°C, N = 7 (B); 28.5°C, N = 9 (C)] following 5 days of entrainment with various temperature cycles [(A) 12 hours at 22.5°C/12 hours at 25.5°C; (B) 12 hours at 25.5°C/12 hours at 28.5°C; (C) 12 hours at 28.5°C/12 hours at 31.5°C]. The detrended data are presented as means ± SD. Period (D) and amplitude (E) of the bioluminescent signal of the data from (A) through (C) are shown as single data points, median, and interquartile range. Data were analyzed using ordinary one-way analysis of variance (ANOVA). NS, not significant (P > 0.05); **P = 0.0013, *P = 0.0311. See also table S1.

  • Fig. 4 Phase angle of entrainment in T cycles.

    PytvA::lux was cultured under symmetrical temperature cycles [alternations between 25.5°C (50% of cycle) and 28.5°C (50% of cycle)] using different cycle lengths (T) [T20 (a 20-hour zeitgeber cycle): N = 17; T22 (a 22-hour zeitgeber cycle): N = 16; T24 (a 24-hour zeitgeber cycle): N = 26]. The phase [peak of luciferase expression; expressed as external time (ExT), where midnight is 0] shifted to a later phase with shorter temperature cycles. The blue shaded areas indicate the cold phase, and the pink shaded areas indicate the warm phase. The graph on the left shows median period with the interquartile range. The graph on the right is a violin plot of the same data. Phases observed in the different T cycles were compared using ordinary one-way ANOVA. All comparisons were significantly different from each other (****P < 0.0001, ***P = 0.0005).

Supplementary Materials

  • Supplementary Materials

    A circadian clock in a nonphotosynthetic prokaryote

    Zheng Eelderink-Chen, Jasper Bosman, Francesca Sartor, Antony N. Dodd, Ákos T. Kovács, Martha Merrow

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    • Figs. S1 to S9
    • Table S1

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