Composition and antimicrobial activity of fatty acids detected in the hygroscopic secretion collected from the secretory setae of larvae of the biting midge Forcipomyia nigra (Diptera: Ceratopogonidae).
The hygroscopic secretion produced by the secretory setae of terrestrial larvae of the biting midge Forcipomyia nigra (Winnertz) was analysed using gas chromatography coupled with mass spectrometry (GC-MS). The viscous secretion is stored at the top of each seta and absorbs water from moist air. GC-MS analyses (four independent tests) showed that the secretion contained 12 free fatty acids, the most abundant of which were oleic (18:1), palmitic (16:0), palmitoleic (16:1) and linoleic (18:2). Other acids identified were valeric (5:0), enanthic (7:0), caprylic (8:0), pelargonic (9:0), capric (10:0), lauric (12:0), myristic (14:0) and stearic (18:0). Two other compounds, glycerol and pyroglutamic acid, were also found. The antibacterial activity of the fatty acids and pyroglutamic acid was tested using the agar disc diffusion method and targeted Gram positive (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis) and Gram negative bacterial strains (Citrobacter freundii, Pseudomonas aeruginosa, Pseudomonas fluorescens). The antifungal activity was tested by determining minimal inhibitory concentration (MIC) of examined compounds. Fatty acids were tested against enthomopathogenic fungi (Paecilomyces lilacinus, Paecilomyces fumosoroseus, Lecanicillium lecanii, Metarhizium anisopliae, Beauveria bassiana (Tve-N39), Beauveria bassiana (Dv-1/07)). The most effective acids against bacterial and fungal growth were C(9:0), C(10:0) and C(16:1), whereas C(14:0), C(16:0,) C(18:0) and C(18:1) demonstrated rather poor antifungal activity and did not inhibit the growth of bacteria. The antimicrobial assay investigated mixtures of fatty and pyroglutamic acids (corresponding to the results of each GC-MS test): they were found to be active against almost all the bacteria except P. fluorescens and also demonstrated certain fungistatic activity against enthomopathogenic fungi. The hygroscopic secretion facilitates cuticular respiration and plays an important role in the antimicrobial protection of F. nigra larvae living in moist terrestrial habitats.
Department of Invertebrate Zoology, University of Gdańsk, Al. Piłsudskiego 46, 81-378 Gdynia, Poland. dokale@ug.edu.pl
Aleksandra
A
Urbanek
Ryszard
R
Szadziewski
Piotr
P
Stepnowski
Joanna
J
Boros-Majewska
Iwona
I
Gabriel
Małgorzata
M
Dawgul
Wojciech
W
Kamysz
Danuta
D
Sosnowska
Marek
M
Gołębiowski
D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis*; D000935:Antifungal Agents / Q000032:analysis*; D002519:Ceratopogonidae / Q000737:chemistry* / Q000648:ultrastructure; D002849:Chromatography, Gas; D005227:Fatty Acids / Q000737:chemistry*; D005990:Glycerol / Q000032:analysis; D007814:Larva / Q000737:chemistry / Q000648:ultrastructure; D013058:Mass Spectrometry; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D011761:Pyrrolidonecarboxylic Acid / Q000032:analysis; D058618:Sensilla / Q000378:metabolism* / Q000648:ultrastructure
D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D005227:Fatty Acids; D005990:Glycerol; D011761:Pyrrolidonecarboxylic Acid