Biosurfactants in Dwarf Mistletoe (Arceuthobium)
flowering plants that parasitize members of Pinaceae and Cupressaceae throughout North America, Central America, Asia, and Africa. As DMT is an aerial parasite that disrupts water relations, we suspected that he plant might contain biosurfactants, biologically-derived agents that act to lower surface tension. Using an oil drop assay coupled to image analysis, we detected biosurfactants in a crude methanol extract from stem tissue and subsequently performed three purification steps, quantifying the extract at each successive stage of purification in its ability to reduce surface tension. The biosurfactant in the final purified sample elicited a spread of 4.31 ± 0.15 mm in the oil drop assay. This value, which is significantly different than those of the negative controls (p<0.01), reflects a drop in water surface tension from 72 mN/m to under 30 mN/m, a purification factor of 575-fold, and a significantly more active (p<0.05) purified sample relative to the crude. The biosurfactant has a critical micellar concentration (CMC) of 8.50 g/L and consists of a short alkyl chain with aromatic groups and peptide bonds, based on preliminary 1H and 13C NMR spectroscopic analysis. These structural components are more consistent with a bacterially-produced polymyxin as opposed to a plantproduced saponin. The polarity of the DMT biosurfactant lies between the polarity of chloroform and that of a 6:4 methanol:water solution.
Key Words: Arceuthobium americanum, biosurfactants, dwarf mistletoe, oil drop assay, parasite, surface tension, surfactin, water relations.