A mixed community of actinomycetes produce multiple antibiotics for the fungus farming ant Acromyrmex octospinosus.
BACKGROUND
Attine ants live in an intensely studied tripartite mutualism with the fungus Leucoagaricus gongylophorus, which provides food to the ants, and with antibiotic-producing actinomycete bacteria. One hypothesis suggests that bacteria from the genus Pseudonocardia are the sole, co-evolved mutualists of attine ants and are transmitted vertically by the queens. A recent study identified a Pseudonocardia-produced antifungal, named dentigerumycin, associated with the lower attine Apterostigma dentigerum consistent with the idea that co-evolved Pseudonocardia make novel antibiotics. An alternative possibility is that attine ants sample actinomycete bacteria from the soil, selecting and maintaining those species that make useful antibiotics. Consistent with this idea, a Streptomyces species associated with the higher attine Acromyrmex octospinosus was recently shown to produce the well-known antifungal candicidin. Candicidin production is widespread in environmental isolates of Streptomyces, so this could either be an environmental contaminant or evidence of recruitment of useful actinomycetes from the environment. It should be noted that the two possibilities for actinomycete acquisition are not necessarily mutually exclusive.


RESULTS
In order to test these possibilities we isolated bacteria from a geographically distinct population of A. octospinosus and identified a candicidin-producing Streptomyces species, which suggests that they are common mutualists of attine ants, most probably recruited from the environment. We also identified a Pseudonocardia species in the same ant colony that produces an unusual polyene antifungal, providing evidence for co-evolution of Pseudonocardia with A. octospinosus.


CONCLUSIONS
Our results show that a combination of co-evolution and environmental sampling results in the diversity of actinomycete symbionts and antibiotics associated with attine ants.
Barke
Jörg
J
School of Biological Sciences, University of East Anglia, Norwich, Norwich Research Park, UK.
Seipke
Ryan F
RF
Grüschow
Sabine
S
Heavens
Darren
D
Drou
Nizar
N
Bibb
Mervyn J
MJ
Goss
Rebecca J M
RJ
Yu
Douglas W
DW
Hutchings
Matthew I
MI
D000192:Actinomycetales / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000935:Antifungal Agents; D001000:Ants / Q000382:microbiology*; D001483:Base Sequence; D001681:Biological Assay; D005075:Biological Evolution; D002174:Candicidin / Q000096:biosynthesis*; D002853:Chromatography, Liquid; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D013559:Symbiosis; D053719:Tandem Mass Spectrometry
D000935:Antifungal Agents; D002174:Candicidin
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