DOI: 10.5061/dryad.k0p2ngf4v
title: Formicine ants swallow their highly acidic poison for gut microbial selection and control

description: Animals continuously encounter microorganisms that are essential for
 health or cause disease. They are thus challenged to control harmful
 microbes while allowing acquisition of beneficial microbes. This challenge
 is likely especially important for social insects with respect to microbes
 in food, as they often store food and exchange food among colony members.
 Here we show that formicine ants actively swallow their antimicrobial,
 highly acidic poison gland secretion. The ensuing acidic environment in
 the stomach, the crop, can limit the establishment of pathogenic and
 opportunistic microbes ingested with food and improve survival of ants
 when faced with pathogen contaminated food. At the same time, crop acidity
 selectively allows acquisition and colonization by Acetobacteraceae, known
 bacterial gut associates of formicine ants. This suggests that swallowing
 of the poison in formicine ants acts as a microbial filter and that
 antimicrobials have a potentially widespread but so far underappreciated
 dual role in host-microbe interactions.
description: <strong>Data Fig.1a: </strong>Source data on pH of
 crop lumens at 4h, 24h and 48h after feeding <i>C.
 floridanus</i> ants 10% honey water at 0h and at 4h after re-feeding
 ants at 48h. <strong>Data Fig.1b:</strong>
 Source data on pH of crop lumens in<i> C. floridanus</i> ants
 that were either prevented to ingest formic acid containing poison gland
 secretions (FA-) or not (FA+) for 24h after feeding.
 <strong>Data Fig.1c:</strong> Source data on pH of
 crop lumens 24h after feeding in seven formicine ant species that were
 either prevented to ingest formic acid containing poison gland secretions
 (FA-) or not (FA+). <strong>Data
 Fig.1-supplementary figure 1:</strong> Source Data on the baseline
 acidity of <i>C. floridanus</i> (major and minor worker caste)
 under satiated and starved conditions.
 <strong>Data Fig.1-supplementary figure 2:</strong>
 Source data on the frequency of acidopore grooming in <i>C.
 floridanus</i> ants within 30 min. after fluid ingestion (water or
 10% honey water) compared to ants that did not receive any fluid
 (unfed). <strong>Data Fig.1-supplementary figure
 3:</strong> Source data on pH-measurements 24h after access to 10%
 honey-water in the crop and directly after the proventriculus at four
 points along the midgut of <i>C. floridanus</i>
 ants. <strong>Data Fig.2a,b:
 </strong>Source data on the number and the change in the number of
 colony forming units (CFUs) relative to 0h in the crop in the crop (a) and
 midgut (b) part of the digestive tract of <i>C. floridanus</i>
 ants at 0h, 0.5h, 4h, 24h, and 48h after feeding ants 10% honey water
 contaminated with <i>Serratia marcescens.</i>
 <strong>Data Fig.2-supplementary figure 1:
 </strong>Source data on the food passage of florescent particles
 through the digestive tract (crop, midgut, hindgut) of <i>C.
 floridanus</i> minor (a) and major (b) worker ants.
 <strong>Data Fig.2-supplementary figure 2a,b:
 </strong>Source data on the number and the change in the number of
 colony forming units (CFUs) in the crop (a) and midgut (b) part of the
 digestive tract of <i>C. floridanus</i> ants relative to 0h in
 the crop at 0h, 0.5h, 4h, 24h, and 48h after feeding ants 10% honey water
 contaminated with <i>Escherichia coli</i>.
 <strong>Data Fig.2-supplementary figure 3:
 </strong>Source data on the number and the change in the number of
 CFUs relative to pH 5 after incubation of <i>Serratia
 marcescens</i> in 10% honey water (pH = 5) or in 10% honey water
 acidified with commercial formic acid to a pH of 4, 3 or 2 for
 2h. <strong>Data Fig.3: </strong>Source
 data on the survival of individual <i>C. floridanus</i> ants
 that were either prevented to ingest formic acid containing poison gland
 secretions (FA-) or not (FA+) after feeding on either honey water
 contaminated with <i>Serratia marcescens</i>
 (<i>Serratia</i>+) or non-contaminated honey water
 (<i>Serratia</i>-). <strong>Data
 Fig.4: </strong>Source data on the survival of donor <i>C.
 floridanus</i> ants that were directly fed with pathogen
 contaminated food and were either prevented to ingest formic acid
 containing poison gland secretions (FA-) or not (FA+) and survival of
 receiver ants that received pathogen contaminated food only through
 trophallaxis with donor ants and were always prevented to ingest formic
 acid containing poison gland secretions (FA-).
 <strong>Data Fig.4-supplementary figure 1:</strong>
 Total duration of trophallaxis events within 30 min. of the first bout of
 food exchange between donor-receiver ant-pairs of <i>C.
 floridanus</i> ants. Donor ants in both pairs were directly fed with
 <i>Serratia marcescens</i> contaminated 10% honey water and
 were either prevented to ingest formic acid containing poison gland
 secretions (FA-) or not (FA+), while receiver ants received pathogen
 contaminated food only through trophallaxis with the respective donor ants
 and were always prevented to ingest formic acid containing poison gland
 secretions (FA-). <strong>Data Fig.5a,b:
 </strong>Source data on the number and the change in the number of
 colony forming units (CFUs) relative to 0h in the crop in the crop (a) and
 midgut (b) part of the digestive tract of <i>C. floridanus</i>
 ants at 0h, 0.5h, 4h, 24h, and 48h after feeding ants 10% honey water
 contaminated with <em>Asaia</em> sp.
 <strong>Data Fig.5-supplementary figure 1:
 </strong>Source data on the number and the change in the number of
 CFUs relative to pH 5 after incubation of <i>Asaia</i> sp. in
 10% honey water (pH = 5) or in 10% honey water acidified with commercial
 formic acid to a pH of 4, 3 or 2 for 2h.
 <strong>Data Code and Script file:</strong> File
 containing all code required to reproduce the analyses and figures in R
 version 3.6.1.