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Programmed death in a unicellular organism has species-specific fitness effects - PubMed

  • ️Wed Jan 01 2014

Programmed death in a unicellular organism has species-specific fitness effects

Pierre M Durand et al. Biol Lett. 2014.

Abstract

Programmed cell death (PCD) is an ancient phenomenon and its origin and maintenance in unicellular life is unclear. We report that programmed death provides differential fitness effects that are species specific in the model organism Chlamydomonas reinhardtii. Remarkably, PCD in this organism not only benefits others of the same species, but also has an inhibitory effect on the growth of other species. These data reveal that the fitness effects of PCD can depend upon genetic relatedness.

Keywords: Chlamydomonas reinhardtii; inclusive fitness; programmed cell death.

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Figures

Figure 1.
Figure 1.

PCD induction and detection. PCD was induced in C. reinhardtii CC125 using heat and confirmed using DNA fragmentation patterns and PS exposure. (a) Genomic DNA fragmentation profiles in C. reinhardtii CC125. Lane 1: 100 bp DNA ladder; lane 2: untreated control; lane 3: heat-induced PCD. (b) Flow cytometric analysis. I and II are dot-plots of a sample (30 000 cells) of the population of control and heat-induced PCD cells, respectively. Axes are: (x) AV FITC fluorescence and (y) PI fluorescence. The four quadrants are as follows: (i) lower left comprises normal, healthy cells (isotype control, AV− and PI−); (ii) lower right comprises early PCD cells (AV+ and PI−); (iii) upper right comprises late PCD (AV+ and PI+) and (iv) upper left comprises necrotic cells (AV− and PI+).

Figure 2.
Figure 2.

Differential fitness effects of PCD supernatant. Culture absorbances and cell counts are for two strains of C. reinhardtii (CC125 and UTEX89) and two other species C. moewusii and C. debaryana. PCD supernatant was obtained from C. reinhardtii CC125 cultures and supplemented with TAP medium (1 : 2). The fitness effects of PCD supernatant were determined spectrophotometrically (absorbance at 665 nm) and by direct cell counts (average of four readings). Supernatant from an untreated (non-PCD) C. reinhardtii CC125 culture was used as the control. PCD supernatant had a beneficial effect on the growth of others of the same species and strain according to (a) a statistically significant difference in absorbances (p = 0.03) and (b) an obvious, albeit not statistically significant, trend in count comparisons (p = 0.39), the latter possibly due to the relatively small sample size. Unexpectedly, PCD supernatant from C. reinhardtii CC125 inhibited the growth of two other species C. moewusii and C. debaryana for both absorbance (p = 0.02 in both species) and count comparisons p = 0.03 and p = 0.02, respectively (c–f). The effect on the same species, different strain was not significant (absorbances p = 0.30; counts p = 0.71, g,h). Error bars are ±1 s.d. (n = 4).

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