Antimicrobial Synergism and the Spindle Tree

Fruit of Spindle Tree, Euonymus europaeus

Though the fine weather of the summer has given way to storm warnings and cold, dark mornings, its memory still lingers in the fruit of the Spindle Tree (Euonymus europaeus). This native shrub usually produces very distinctive, shocking pink, three to four lobed fruit from September to October (1) that is quickly eaten by blackbirds. This year, the summer has given a plentiful harvest of fruit that has until now meant many E. europaeus berries have gone untouched.

Spindle Tree, Euonymus europaeus

E. europaeus has proved to be quite useful: its hard timber was used to make skewers and spindles for spinning wool (hence the common name (1)). It has also been shown to produce secondary metabolites with remarkable antimicrobial abilities. Van den Bergh et al. (2) isolated a hevein-type antimicrobial peptide in 2002 from the bark of E. europaeus that show excellent antimicrobial activity against plant pathogenic fungi such as Fusarium oxysporum, Pythium ultimum and Rhizoctonia solani and Gram-positive bacteria such as Bacillus megaterium. This E. europaeus chitin-binding protein or Ee-CBP was also shown to be very stable as activity was not affected by boiling for ten minutes or prolonged storage.

Bark of Spindle Tree, Euonymus europaeus

A  further chitin binding protein was also isolated (3) that acted as a classical class I chitinase (Ee-chitinase) which was not as potent as the Ee-CBP. However, the Ee-CBP and Ee-chitinase displayed a pronounced synergistic effect in assays against fungal activity. These proteins have potential to be used in genetic engineering for biological control of plant diseases.

References

1. Phillips, 1978 Wild Flowers of Britain pp. 58 and 172
2. Van den Bergh et al., 2002 FEBS Letters 530 pp. 181-185
3. Van den Bergh et al., 2004 Planta 219 pp. 221–232