Nepenthes pitfall traps are an anti-microbial environment

Nepenthes pitfall traps are a microbe-unfriendly environment

Nepenthes pit­fall traps are a microbe-unfriendly environment

Carnivorous or insect­i­vor­ous plants fas­cin­ate people, includ­ing sci­ent­ists such as Charles Darwin. He was the first to write a book on this topic (Darwin, 1875). Although Darwin described plants equipped with pit­fall traps, he never saw spe­cies of the genus Nepenthes which occur in south-east Asia.

Like other car­ni­vor­ous plants, Nepenthes spe­cies grow on poor soil. Therefore, they need to com­ple­ment their min­eral nutri­ents – primar­ily with nitro­gen and phos­phorus – from caught and diges­ted prey. When vis­it­ing the pit­fall traps, the attrac­ted prey, mainly arth­ro­pods, falls into the trap, drowns and is diges­ted by the enzyme cock­tail of the pitcher fluid. Because the digest­ive liquid can be eas­ily har­ves­ted from the pitcher, Nepenthes plants are ideal objects to study enzymes and other com­pounds involved in this plant car­ni­vory. As a con­sequence, com­pared with other car­ni­vor­ous taxa, the pro­tein com­pos­i­tion of the digest­ive fluid of Nepenthes is fairly well ana­lysed and documented.

Due to the fact that closed Nepenthes pitch­ers have no dir­ect con­tact with the envir­on­ment, it has been widely claimed that their pitcher fluid is sterile and that all pro­teins and com­pounds iden­ti­fied in this pitcher fluid are solely plant-derived. Interestingly, only two exper­i­ments have been con­duc­ted to demon­strate the ster­il­ity of pitcher liquid: fluid taken from a closed pitcher was plated either on plain nutri­ent agar (Hepburn, 1918) or on meat agar plates (Lüttge, 1964) and incub­ated for sev­eral days. In no case was any bac­terial growth detec­ted and the authors con­cluded that the pitcher fluid is sterile. However, the pres­ence of microbes can­not be excluded by such simple exper­i­ments because most micro-organisms can­not be grown in culture.

Researchers have now ana­lysed the com­pos­i­tion of Nepenthes digest­ive fluid from closed pitch­ers to reveal whether or not pitch­ers are really sterile inside and how these plants man­age to keep micro­bial growth under con­trol. The con­tent of pro­teins, inor­ganic ion com­pos­i­tions and sec­ond­ary meta­bol­ites were stud­ied. In addi­tion, the effect of pitcher fluid on micro­bial growth was invest­ig­ated. The res­ults reveal that the fluid of closed Nepenthes pitch­ers is com­posed provides anti-microbial con­di­tions. Thus these plants can avoid, at least to some extent, the growth of microbes that com­pete with the plant for the prey-derived nutri­ents avail­able in the pitcher.


Franziska Buch, Matthias Rott, Sandy Rottloff, Christian Paetz, Ines Hilke, Michael Raessler and Axel Mithöfer. Secreted pitfall-trap fluid of car­ni­vor­ous Nepenthes plants is unsuit­able for micro­bial growth. (2013) Annals of Botany 111 (3): 375–383
Carnivorous plants of the genus Nepenthes pos­sess mod­i­fied leaves that form pit­fall traps in order to cap­ture prey, mainly arth­ro­pods, to make addi­tional nutri­ents avail­able for the plant. These pitch­ers con­tain a digest­ive fluid due to the pres­ence of hydro­lytic enzymes. In this study, the com­pos­i­tion of the digest­ive fluid was fur­ther ana­lysed with regard to min­eral nutri­ents and low molecular-weight com­pounds. A poten­tial con­tri­bu­tion of microbes to the com­pos­i­tion of pitcher fluid was invest­ig­ated. Fluids from closed pitch­ers were har­ves­ted and ana­lysed for min­eral nutri­ents using ana­lyt­ical tech­niques based on ion-chromatography and induct­ively coupled plasma–optical emis­sion spec­tro­scopy. Secondary meta­bol­ites were iden­ti­fied by a com­bin­a­tion of LC-MS and NMR. The pres­ence of bac­teria in the pitcher fluid was invest­ig­ated by PCR of 16S-rRNA genes. Growth ana­lyses of bac­teria and yeast were per­formed in vitro with har­ves­ted pitcher fluid and in vivo within pitch­ers with injec­ted microbes. The pitcher fluid from closed pitch­ers was found to be primar­ily an approx. 25-mM KCl solu­tion, which is free of bac­teria and unsuit­able for micro­bial growth prob­ably due to the lack of essen­tial min­eral nutri­ents such as phos­phate and inor­ganic nitro­gen. The fluid also con­tained anti­mi­cro­bial naph­thoquinones, plum­ba­gin and 7-methyl-juglone, and defens­ive pro­teins such as the thaumatin-like pro­tein. Challenging with bac­teria or yeast caused bac­ter­icide as well as fungi­static prop­er­ties in the fluid. Our res­ults reveal that Nepenthes pitcher flu­ids rep­res­ent a dynamic sys­tem that is able to react to the pres­ence of microbes. The secreted liquid of closed and freshly opened Nepenthes pitch­ers is exclus­ively plant-derived. It is unsuit­able to serve as an envir­on­ment for micro­bial growth. Thus, Nepenthes plants can avoid and con­trol, at least to some extent, the micro­bial col­on­iz­a­tion of their pit­fall traps and, thereby, reduce the need to vie with microbes for the prey-derived nutrients.


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AJ Cann. ORCID 0000-0002-9014-3720

Alan Cann is a Senior Lecturer in the School of Biological Sciences at the University of Leicester and formerly Internet Consulting Editor for AoB.

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