2001–2002 - California Sea Grant - UC San Diego

of the alpha subclass of proteobacteria. His conclusion: these
proteobacteria must play a key role in protecting eggs. And, he speculates
that their common bacterial-defense mechanism has probably remained
relatively unchanged during the many millions of
years it took for different squid species to evolve and
geographically separate.
Though similarities abound, Epel also reported
some intriguing differences in the symbiotic bacteria
associated with each species. Whereas none of the
individually cultured symbiotic bacteria on the
market squid produced antibiotic compounds, two of
the other three species did: Sepia officinalis and S.
pharaonis. In ongoing Sea Grant research, Epel is
collaborating with marine natural chemist Dr.
William Fenical of Scripps Institution of Oceanography,
also a Sea Grant researcher, to purify and
identify antibiotic molecules produced by these
bacteria.
So, how then does the market squid protect its
eggs? The leading theory is that the complex suite of
bacteria must be present to mount a response against
infection. In this scenario, the mechanism for
defense is called quorum sensing, meaning that key
bacteria must be present in sufficient numbers to interact with each other
and produce antibiotics.
“While the public may retain its
faith in an antibiotic shield against
infection, in reality, for every class
of antimicrobial drugs developed by
the pharmaceutical industry,
there’s a mechanism of resistance
before much time elapses.
Therapies once standard for
infections have become largely
ineffective.”
—A 1999 report from an advisory
panel convened by the National
Institutes of Health, National
Institute of Nursing Research
To test this, Epel is collaborating with a researcher at the University of
Iowa who has developed a technique for detecting what are known as acylhomoserine
lactones, signal molecules associated with communication
between proteobacteria. That is a fancy way of
saying Epel is out to learn “who is talking to whom
and in what language.” The idea, he explained, is
that bacteria emit chemical signals that stimulate
other bacteria to produce antibiotics or fungicides.
If this novel form of antimicrobial defense is
indeed what is happening, it could mean that
these antibiotic compounds are also working
through novel biochemical pathways. This, he
said, offers the best chance against supergerms.
Long-time Sea Grant researcher David Epel is
the Jane and Marshall Steel, Jr. Professor in
Marine Sciences Cell and Developmental
Biology at Stanford. Photo: Stanford University
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