Green Plants Share Bacterial Toxin

Nov 06, 2006
Green Plants Share Bacterial Toxin
Green fluorescence shows lipid A, previously known only as a toxin from bacteria, in leaves from pea seedlings. ((Peter Armstrong/UC Davis photo)

A toxin that can make bacterial infections turn deadly is also found in higher plants, researchers at UC Davis, the Marine Biology Laboratory at Woods Hole, Mass. and the University of Nebraska have found. Lipid A, the core of endotoxin, is located in the chloroplasts, structures that carry out photosynthesis within plant cells.

The lipid A in plant cells is evidently not toxic. The human intestine contains billions of Gram-negative bacteria, but lipid A does not become a problem unless bacteria invade the bloodstream.

"We've no idea what it's doing, but it must be something important because it's been retained for a billion years of evolution of plant chloroplasts," said Peter Armstrong, professor of molecular and cellular biology at UC Davis and senior author on the paper.

Endotoxin is better known to bacteriologists and physicians as part of the outer coat of Gram-negative bacteria such as E. coli. The lipid A core of bacterial endotoxin activates the immune system and can cause septic shock, a major cause of death from infection. It is distinct from the toxin found in E. coli strain 0157, responsible for the recent outbreak of food poisoning tied to spinach.

Bacteria were thought to be the only source of lipid A. However, R.L. Pardy, professor at the University of Nebraska-Lincoln, recently found a similar molecule in Chlorella, a single-celled relative of more advanced plants. Armstrong's lab at UC Davis developed methods to visualize lipid A in cells, using a protein from the immune system of the horseshoe crab, and the researchers began collaborating.

"It was one of those celebratory moments, when I looked in the microscope and saw these gloriously stained algal cells," Armstrong said, describing their first experiment. The group has now found lipid A in chloroplasts of garden pea plants as well as green algae, and Armstrong suspects that it is present in all higher plants with chloroplasts.

That idea is supported by genetics. Sequencing of the Arabidopsis genome -- the first higher plant to have its entire DNA sequence read -- revealed that the common lab plant has all the biochemical machinery to make lipid A, an observation that had gone largely unnoticed until now. Chloroplasts themselves are thought to have evolved from cyanobacteria, independent photosynthetic bacteria that took up residence in ancestral plant cells.

Source: UC Davis

Explore further: Illuminating the dark side of the genome

add to favorites email to friend print save as pdf

Related Stories

Designing exascale computers

Jul 23, 2014

"Imagine a heart surgeon operating to repair a blocked coronary artery. Someday soon, the surgeon might run a detailed computer simulation of blood flowing through the patient's arteries, showing how millions ...

Essential oils may provide good source of food preservation

Jul 21, 2014

A new study in the Journal of Food Science, published by the Institute of Food Technologists (IFT), found that essential oils may be able to be used as food preservatives in packaging to help extend the shelf-life of foo ...

New membrane-synthesis pathways in bacteria discovered

Jun 13, 2014

Biologists at the Ruhr-Universität Bochum (RUB) have discovered new mechanisms used by bacteria to manufacture lipids, i.e. fat molecules, for the cell membrane. Those mechanisms are a combination of familiar ...

Recommended for you

Illuminating the dark side of the genome

1 hour ago

Almost 50 percent of our genome is made up of highly repetitive DNA, which makes it very difficult to be analysed. In fact, repeats are discarded in most genome-wide studies and thus, insights into this part ...

Breakthrough in coccidiosis research

19 hours ago

Biological researchers at the Royal Veterinary College (RVC) are a step closer to finding a new cost-effective vaccine for the intestinal disease, coccidiosis, which can have devastating effects on poultry ...

User comments : 0