The gut bacteria symbionts from the monophagous insect Acrobasis nuxvorellaproduce tannase for the digestion of Carya illinoinensis tannins

Abstract

• Acrobasis nuxvorella larvae contain gut symbionts that produce tannase enzymes. • The bacteria Bacillus pumilus strains: LB66, LB24, and TT29 presented different tannase activity. • The bacteria Bacillus pumilus strains: LB66, LB24, and TT29 and Sthaphylococcus warneri (TP8) were able to hydrolyze tannic acid releasing gallic acid and glucose. • Sthaphylococcus warneri (TP8) there are no previous reports to be a tannase producer. Acrobasis nuxvorella Neuzing (Lepidoptera: Pyralidae), or the Pecan Nut Casebearer (PNC), is a monophagous pecan nut [ Carya illinoinensis (Wang) K. Koch] herbivore. This insect has caused major crop losses, despite pecan nut trees producing a high concentration of tannins, which are deterrent compounds for insects. The PNC consumes and processes tannin-rich tissues without any negative effects on its nutrition. Certain bacterial species of the herbivore gut microbiota have been proven to produce tannase, therefore, we hypothesize that the PNC has symbiotic bacteria that produce tannase for the digestion of tannin contained in their food. In this work, live PNC larvae were extracted from pecan nutlets. The larval guts were dissected and their contents were cultured to obtain the cultivable bacteria. A total of 224 bacterial isolates were recovered, 19 of which tested positive for tannase activity. Isolates LB66, LB24, TT29, and TP8 displayed comparable activity to the control strain Pseudomonas aeruginosa . Further enzyme semi-purification steps showed specific tannase activity values in the range of 39.5–3.7 U/mg of protein. The isolates were identified as Bacillus pumilus strain TT29, Bacillus pumilus strain LB66, Bacillus pumilus strain LB24 and Sthaphylococcus warneri (TP8) by 16S ribosomal RNA gene sequencing. Our findings indicate that PNC larvae contain gut bacteria able to produce tannase that hydrolyze the galloyl ester bonds in tannins.