Bacteria facilitate prey retention by the pitcher plant Darlingtonia californica

Abstract

Bacteria are hypothesized to provide a variety of beneficial functions to plants. Many carnivorous pitcher plants, for example, rely on bacteria for digestion of captured prey. This bacterial community may also be responsible for the low surface tensions commonly observed in pitcher plant digestive fluids, which might facilitate prey capture. I tested this hypothesis by comparing the physical properties of natural pitcher fluid from the pitcher plant Darlingtonia californica and cultured 'artificial' pitcher fluids and tested these fluids' prey retention capabilities. I found that cultures of pitcher leaves' bacterial communities had similar physical properties to raw pitcher fluids. These properties facilitated the retention of insects by both fluids and hint at a previously undescribed class of plant-microbe interaction.

How a sticky fluid facilitates prey retention in a carnivorous pitcher plant (Nepenthes rafflesiana)

“…californica PF were reproduced by inoculating sterile growth media with bacteria from PF [20]. This suggests that the bacterial community within D. californica pitchers not only help to break down organic matter [49] but also help lower the ST and improve prey retention.…”

“…Additionally, an oiled needle repeatedly floated on water despite vigorous perturbation, while it readily sank in S. flava PF [18]. Quantitative ST measurements support these observations: fluids from open pitchers of S. flava and D. californica both produced ST values lower than water (66 mN/m and 47.9 mN/m, respectively) [18,20]. These findings confirm that ST is reduced in Sarraceniaceae PF, producing an air-fluid interface that is easier to penetrate than water.…”

“…and Darlingtonia californica demonstrated that ants sank more rapidly in digestive fluid than in water [18][19][20]. Importantly, insects rescued at the end of the retention trials survived, which indicate that the high retention rates are unlikely caused by noxious compounds released into the fluid.…”

“…Such striking differences in retention rates of pitcher fluid compared to water have also been reported in several members of the Sarraceniaceae family, which independently evolved pitfall traps to catch prey. Experiments using digestive fluid from Sarracenia flava , S. sledgei (synonym S. alata ) , S. drummondii (synonym S. leucophylla ), and Darlingtonia californica demonstrated that ants sank more rapidly in digestive fluid than in water [18–20]. Importantly, insects rescued at the end of the retention trials survived, which indicate that the high retention rates are unlikely caused by noxious compounds released into the fluid.…”

“…Another property of PF that has been pursued in previous studies is the fluid’s surface tension (ST). Several studies have reported that insects sink more readily in PF than in water [16,18–20,23,24]. In Sarraceniaceae, ants sank rapidly in Heliamphora sp.…”