Microbiologists
have discovered a new glycocin, a small antimicrobial peptide with a sugar
group attached, which is produced by a thermophilic bacterium and is stable at
relatively high temperatures. They also succeeded in transferring the genes
required to produce this glycocin to an E. coli bacterium. This makes it easier
to produce and investigate this compound, which could potentially be used in
biofuel production.
The
rise of antibiotic resistance has spurred the search for new antimicrobials. Bacteriocins --
peptide toxins produced by bacteria to inhibit growth in similar or related
bacterial strains -- are a possible alternative to the more traditional
antibiotics. Bacteriocins would also be useful to protect high-temperature
fermentations mediated by thermophilic bacteria. But this would require the use
of bacteriocins that are stable at higher temperatures.
'That
is why we were interested to find that the thermophilic bacterium Aeribacillus palladius, isolated from the
soil above an oil well in Lithuania, appeared to produce an antibacterial
peptide,' says University of Groningen Professor of Molecular Biology, Oscar
Kuipers. Thus far, purification and identification of the compound had not been
successful. Therefore, Ph.D. student Arnoldas Kaunietis from Vilnius University
spent almost two years in Kuipers' lab to solve the mystery. He is the first
author on the new paper.
By
analyzing genomic information from the Lithuanian bacteria using BAGEL4
software, developed by Anne de Jong and Auke van Heel in Kuipers' group, genes
that are responsible for the production of the bacteriocin were discovered and
the final gene product was named pallidocin. The BAGEL4 software searches for
gene clusters with the potential ability to produce novel antimicrobials.
The
antimicrobial turned out to be a glycocin, belonging to a class of
post-translationally modified peptides. This means that after its production,
one or more functional groups are added to the peptide. In the case of glycocins,
this functional group is a sugar. 'Only five other glycocins were known thus
far,' says Kuipers.
After
isolating pallidocin, the scientists were able to confirm that it is highly
thermostable and exhibits extremely strong activity against specific
thermophilic bacteria. Furthermore, by using the sequence of pallidocin
biosynthesis genes in BAGEL4, two similar peptides were discovered in two
different strains of Bacillus bacteria. These peptides, named Hyp1 and Hyp2,
were also successfully expressed in the E. coli strain. 'This shows that the
expression system works well for various glycocins; it is able to produce them
in vivo', says Kuipers.
Pallidocin
might be useful in high-temperature fermentations, which are used to produce
biofuels or chemical building blocks. The higher temperature makes it easier to
recover volatile products such as ethanol but also reduces the risk of
contamination with common bacteria. However, contamination with thermophilic
bacteria is possible. 'Both pallidocin and Hyp1 appear to be active against
thermophilic bacteria and some Bacillus species,' says Kuipers. And there could
be more applications: 'Contamination by thermophiles is also a problem in the
food industry.'
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