Acacia, ants and antibiotics: Protect and survive; Another twist in one of nature’s best-known partnerships
January 26, 2014 Leave a comment
Acacia, ants and antibiotics: Protect and survive; Another twist in one of nature’s best-known partnerships
Jan 25th 2014 | From the print edition
THE symbiosis between bullhorn acacias and Pseudomyrmex ferruginea, the bullhorn acacia ant, is the stuff of biological legend. The acacias provide the ants with food, in the form of protein, fat and sugar secreted for their delectation by special organs called Beltian bodies, and also with homes, in the hollow thorns which give the plant its name. The ants reciprocate by stinging anything—from other insects to cattle—that dares try to eat the acacia’s leaves. The latest research, though, suggests that the ants do more than just drive away herbivores. They also act as a sort of immune system which protects acacias from infection.
This discovery, reported in New Phytologist by Marcia Gonzalez-Teuber of La Serena University, in Chile, dates back to an observation made a decade ago that macaranga trees, which have similar symbiotic relations with ants, seem immune to a particular fungus when ants are present, but not when they aren’t. Dr Gonzalez-Teuber wondered if something like this was true of acacias—and if it was, why.
To try to find out she chose ten wild acacia plants in the state of Oaxaca, in Mexico, and evicted the ants from one branch of each by plucking them off, removing the thorns, and stopping them returning by coating the base of the branch with a sticky substance that traps insects. As a control she sliced the thorns off a second branch, but left the ants free to roam over it.
After six weeks, she found that 45% of the leaves on the experimental branches showed signs of infection, compared with 14% of those (including the thornless controls) over which ants could roam freely. And when she tried culturing micro-organisms from leaves taken from the various branches she showed that those from branches without ants were more heavily infected with known plant pathogens.
The reason, she discovered, was on the ants’ legs. When she and her colleagues amputated some of these, washed them in methanol to see what they could extract, and applied the result to colonies of micro-organisms cultured from acacia leaves, they found that the extract eradicated many of those colonies. When they analysed the extract they discovered it contained several types of bacteria known to synthesise antibiotics. The ants, then, by acting as hosts to these bacteria, are protecting their own hosts from the attentions of other micro-organisms—and making the legend of their mutual relationship with acacias grow yet further in the telling.
About bambooinnovator
Bamboo Innovator 