The researchers the Hebrew University of Jerusalem have reported in Friday's edition of the journal Science that a pentapeptide produced by intestinal bacteria Escherichia coli (E. coli) serves as a communication signal between single bacteria cells.

Although bacteria are unicellular organisms, there is mounting evidence that they don't behave in isolation, instead communicating between themselves and thereby manifesting some multi-cellular behaviours.

The research was carried out by a group headed by Prof. Hanna Engelberg-Kulka of the Department of Molecular Biology at the university.

The peptide activates a built in suicide module called mazEF; one part, mazF is a toxin, while the other part, mazE is an antitoxin that counteracts the effects of mazF. This led to the peptide being dubbed Extracellular Death Factor (EDF)

While suicidal cell death is counterproductive for individual bacterial cells, it becomes effective for the bacterial community as a whole by the simultaneous action of a group of cells that are signalled by EDF. Under stressful conditions, EDF is activated and a major sub-population within the bacterial culture dies, allowing the survival of the population as a whole.

The death of part of the colony may also release components that can form a protective 'biofilm'.

On a practical level, the ability to chemically synthesise an EDF replica could provide a lead for a new and more efficient class of antibiotics that specifically trigger bacterial cell death in E. coli.

The chemical characterisation of the new communication factor was particularly difficult for the researchers because of two main reasons: it is present in the bacterial culture in minute amounts, and the factor decomposes under the conditions that are routinely used during standard chemical characterisation methods.

To get around this, the peptide was first extracted from an E. coli culture using a C-18 SepPak cartridge to separate fractions. Those fractions which contained the peptide were then purified using high-performance liquid chromatography (HPLC). The subsequent analysis using electrospray ionisation mass spectrometry (ESI-MS) was conducted at neutral pH to avoid damaging the peptide.

The research has also identified several bacterial genes that are involved in the generation of the communication factor, said Prof. Engelberg-Kulka.