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2002
LSU-HHMI Summer Undergraduate Research Program |
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 Tiffany
Hierath (Jim Ottea, Dept. of Entomology, LSU Agricultural Center)
An evaluation of lytic peptides as a termiticide
The Formosan termite, Coptotermes formosanus, is a devastating
structural pest in the mid-south. Like other lower termites,
C. formosanus is dependent upon endosymbiont protozoans to break
down the cellulose that they ingest. Without these protozoans,
the termites would starve to death, regardless of the amount
of available food. Due to the nature of this relationship, we
hypothesized that lytic peptides could kill termites if they
could lyse the protozoans. Three peptides; Agni-14 ([Lys Leu
Ala Lys Lys Leu Ala]2), Gagni-21 ([Lys Leu Gly Lys Lys Leu Gly]3),
and Pagni-14 (Lys Phe Ala Lys Lys Phe Ala Lys Phe Ala Lys Phe
Ala) were tested as potential termiticides. All three peptides
were active in vitro and caused lysis of the three predominant
species of protozoans (Spriotrichonympha leidyi, Holomastigote
hartmani, and Psuedotrichonympha grassii) in this termite. Peptide
potencies, expressed as the concentration lethal to 50% of the
total population (LC50), varied among the three peptides and
ranged from 6.5 ?M (Agni-14 on H. hartmani) to >50 ?M (Gagni-21
on P. grassii). In addition, LC50’s for the three peptides
differed depending on the species of protozoan. The most abundant
protozoan species, S. leidyi, was the most susceptible with
an LC50 between 19?M (Pagni-14) and 30?M (Gagni-21). The least
susceptible species was P. grassii with an LC50 ranging from
49?M (Pagni-14) to >50?M (Gagni-21). The LC50 for H. hartmani
ranged from <12?M??Pagni-14) to 33?M??Gagni-21) and was not
as clearly defined as that measured with the other two species
of protozoans. Although the peptides were active in vitro, they
were non-toxic when fed to termites. There was no difference
in mortality of either termites or protozoans measured one week
after treatment. Further experiments to examine pharmacokinetic
aspects that limit toxicity are ongoing.
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