Cultivation reveals physiological diversity among defensive ‘Streptomyces philanthi’ symbionts of beewolf digger wasps (Hymenoptera, Crabronidae)

BMC Microbiology

Research Article

Taras Y Nechitaylo¹  Martin Kaltenpoth¹  Martin Westermann² 

[1] Max Planck Institute for Chemical Ecology, Insect Symbiosis Research Group, Jena, Germany;University Hospital, Centre for Electron Microscopy, Jena, Germany;

关键词: Streptomyces;    Physiology;    Symbiosis;    Mutualism;    Co-evolution;    Beewolf;    Digger wasp;   

DOI  :  10.1186/s12866-014-0202-x

 received in 2014-03-02, accepted in 2014-07-18,  发布年份 2014

来源: Springer

【 摘 要 】

Background‘Candidatus Streptomyces philanthi’ is a monophyletic clade of formerly uncultured bacterial symbionts in solitary digger wasps of the genera Philanthus, Philanthinus and Trachypus (Hymenoptera, Crabronidae). These bacteria grow in female-specific antennal reservoirs and – after transmission to the cocoon – produce antibiotics protecting the host larvae from fungal infection. However, the symbionts’ refractoriness to cultivation has thus far hampered detailed in vitro studies on their physiology and on the evolutionary changes in metabolic versatility in response to the host environment.ResultsHere we isolated in axenic culture 22 ‘Streptomyces philanthi’ biovars from different host species. Sequencing of gyrB revealed no heterogeneity among isolates within host individuals, suggesting low levels of (micro)diversity or even clonality of the symbionts in individual beewolf antennae. Surprisingly, however, isolates from different host species differed strongly in their physiology. All biovars from the Eurasian/African Philanthus and the South American Trachypus host species had high nutritional demands and were susceptible to most antibiotics tested, suggesting a tight association with the hosts. By contrast, biovars isolated from the genus Philanthinus and the monophyletic North American Philanthus clade were metabolically versatile and showed broad antibiotic resistance. Concordantly, recent horizontal symbiont transfer events – reflected in different symbiont strains infecting the same host species – have been described only among North American Philanthus species, altogether indicative of facultative symbionts potentially capable of a free-living lifestyle. Phylogenetic analyses reveal a strong correlation between symbiont metabolic versatility and host phylogeny, suggesting that the host environment differentially affects the symbionts’ evolutionary fate. Although opportunistic bacteria were occasionally isolated from the antennae of different host species, only filamentous Actinobacteria (genera Streptomyces, Amycolatopsis and Nocardia) could replace ‘S. philanthi’ in the antennal gland reservoirs.ConclusionOur results indicate that closely related bacteria from a monophyletic clade of symbionts can experience very different evolutionary trajectories in response to the symbiotic lifestyle, which is reflected in different degrees of metabolic versatility and host-dependency. We propose that the host-provided environment could be an important factor in shaping the degenerative metabolic evolution in the symbionts and deciding whether they evolve into obligate symbionts or remain facultative and capable of a host-independent lifestyle.

【 授权许可】

Unknown   
© Nechitaylo et al.; BioMed Central Ltd 2014. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.