Symbionts provide detoxification

John H. Werren1 Department of Biology, University of Rochester, Rochester, NY 14627

ymbiosis is the intimate “living to- gether” of different organisms (1), S and symbiotic relationships range from mutually beneficial to neutral or parasitic. Indeed, many microbial–host symbioses can vary between these states, depending upon circumstances. Recent years have seen an explosion of discoveries revealing novel microbial–host relation- ships and interactions. In addition to “classic” nutritional symbioses (in which the microbe provides a limiting nutrient not normally available in the host’s diet), studies have shown that microbes can alter Fig. 1. Burkholderia bacteria are found in the soil, where some genotypes are capable of detoxifying the reproductive mode of their hosts (e.g., OP . Stinkbugs acquire bacteria from the environment, and Burkholderia preferentially colo- induce development of unfertilized eggs, nize specialized structures (crypts) in the insect midgut. When stinkbugs are experimentally infected with – pesticide-degrading bacteria, they have significantly increased resistance to pesticide treatment. It is change sex, or cause sperm egg in- unclear whether any Burkholderia genotypes have established a routine transmission cycle between compatibilities), affect mate choice, and bean bugs and the environment, which would enhance coadaptation of in microbes provide protection from natural enemies, and host. including viruses, protozoa, and parasitic insects (2–4). Kikuchi et al. (5) report an nents of the genetic machinery for OP logeny based on 16S ribosomal sequence extension of this repertoire of effects— degradation have also been exchanged indicate no separation of soil- vs. stinkbug- bacteria in the genus Burkholderia impart associated bacteria. Environmental protection against organophosphorous among diverse soil bacteria by lateral gene acquisition of symbionts each genera- pesticides in stinkbugs. transfers. Motivation for the research in- Burkholderia is a genus of biologically cludes possible use of soil microbes for tion has not been widely described in diverse bacteria commonly found in soil environmental remediation of pesticides insects, although it occurs in some other and application of the biochemical systems, such as the squid–Vibrio (light and associated with plants (6). Although – originally isolated as plant pathogens mechanisms to medical treatment of organ), coral algal (nutritional), and Burkholderia . legume–rhizobium (nitrogen fixation) on onion, many are now – known to provide benefits to plants, from A separate research community has symbioses (12 14). involvement in nitrogen fixation to sup- been busy exploring the microbial symbi- In the present study, Kikuchi et al. (5) pression of plant disease. Strains of Bur- oses of insects. The resurgence of symbi- bring together their own observations on kholderia cepacia osis research from its original heyday in Burkholderia in stink bugs with the ob- can also cause chronic Burkholderia lung infections in cystic fibrosis patients. the early to mid-20th century (9) has been servations of involvement in Stinkbug-associated Burkholderia are from spurred by the advent of molecular tools pesticide degradation (7, 8) to develop the a different group within the genus, and for characterizing previously intractable hypothesis that OP-degrading bacteria related strains are found both in soil and bacteria, as well as the discoveries of could impart pesticide resistance to the in the guts of stinkbugs (5). amazing and diverse phenotypic effects of insects. Fenitrothion (FEN) is a commonly – Organophosphorus (OP) compounds symbionts on their hosts (2 4). In previous used OP pesticide, and FEN-degrading Bur- Burkholderia are extensively used in , ac- work, Kikuchi et al. (10) found that strains are found in soils counting for ∼38% of total pesticide use kholderia are common gut bacteria in where these pesticides are applied. In- (7). These compounds inhibit the activity a wide range of stinkbugs and relatives, oculating with FEN-degrading vs. non- encompassing a significant fraction of the degrading strains revealed that pesticide- of acetylcholine esterase, resulting in fi neurotoxic effects in both insects and insect order Heteroptera, or “true bugs.” degrading symbionts impart signi cant mammals. Hence, OPs are common causes Many are major pests in agriculture; for protection against the pesticide applied of poisoning in people and livestock. example, the bean bug Riptortus pedestris under laboratory conditions. Although Burkholderia Because of their heavy use, OP compounds described in the present study. Bur- FEN-degrading were un- fi are also significant contaminants in kholderia normally impart a growth ad- common in local bean elds, treatment of fi terrestrial and aquatic ecosystems. vantage to the bugs, although the precise eld soil brought to the laboratory with Kikuchi et al. (5) bring together the benefit provided is not yet known. Careful FEN greatly enhanced frequency of FEN- Burkholderia findings of two different disciplines. For study also revealed that the bugs acquire degrading , and the stinkbugs several decades researchers have been in- Burkholderia from the environment each reared on soybeans from these soils vestigating how pesticides are degraded in generation as nymphs (11), rather than showed elevated levels of FEN-degrading the environment, discovering a major ro- from the mother (e.g., either within or on activity. Finally, much higher levels of le of soil , including bac- the eggs) or infectiously from other stink- teria in the genus Burkholderia (7, 8). Soil bugs (Fig. 1). The bacteria colonize spe- bacteria can metabolize OPs and use them cialized structures in the posterior midgut Author contributions: J.H.W. wrote the paper. as sources of carbon, phosphorus, or ni- referred to as “crypts” and can achieve The author declares no conflict of interest. 8 trogen, facilitating degradation of these upward of 10 cells per adult. Consistent See companion article on page 8618. compounds in the environment. Compo- with environmental acquisition, their phy- 1E-mail: [email protected].

8364–8365 | PNAS | May 29, 2012 | vol. 109 | no. 22 www.pnas.org/cgi/doi/10.1073/pnas.1206194109 Downloaded by guest on October 7, 2021 COMMENTARY

FEN are used in sugar cane fields on some bacteria and their hosts will be difficult, of both partners and therefore spread of Japanese Islands to control the Oriental unless particular Burkholderia genotypes the resistance phenotype. chinch bug Cavelerius saccharivorus.On The article by Kikuchi et al. (5) focuses one Island, FEN-degrading bacteria were Bacteria in the genus our attention on a potential broad role detected in ∼8% of field-collected chinch for symbionts as chemical detoxifying bugs. The study shows the potential of Burkholderia impart agents in hosts. Surprisingly, the topic has symbiotic bacteria to impart pesticide been largely unstudied (but see refs. 16 resistance to insect hosts. However, as protection against and 17). Given the near ubiquity of mi- noted by the authors, it has not yet been crobial symbioses in nature, ranging from shown that symbionts provide significant organophosphorous inherited microbes in insects to the gut levels of protection in field populations. microbiomes in humans (17, 18), detox- fi Because OP compounds are used so pesticides in stinkbugs. i cation by symbionts could be extremely widely in agriculture for , important. For example, although our liv- symbiont detoxification could represent a ers get much of the credit as a toxin- establish a routine transmission cycle be- degrading organ, our gut microbiome is rapid and previously unappreciated tween environment and host (Fig. 1). It mechanism for pesticide resistance in likely a major player as well (18). Finally, remains possible that stinkbug-adapted lateral gene transfers (LGTs) between insects (15). Given the general de- genotypes occur in some Burkholderia as fi symbionts and hosts are now known to be toxi cation ability of microbes and their “symbiosis islands,” or associated with ability to evolve quickly, they could pro- common (19). Therefore, it would not be plasmids. A clearer picture will emerge surprising if microbe– LGTs of vide a potent means for rapid acquisition from whole-genome sequencing of detoxification genes have occurred during of pesticide resistance in hosts. However, different isolates. evolution in eukaryotic lineages. the mode of microbe transmission to hosts Many insect symbionts can be trans- will affect the likelihood that symbiont- mitted from parent to offspring or are ACKNOWLEDGMENTS. I thank Michael Clark mediated pesticide resistance evolves. readily transferred between insects as (University of Rochester) for producing the For example, given that Burkholderia are “secondary” symbionts (2–4). These graphic for this article. Some images used in the acquired by stinkbugs each generation transmission modes would more readily graphic were kindly provided by Y. Kikuchi (Bio- “ ” fi production Research Institute, Hokkaido Center, from a very large bacterial pool in soil, link bene cial pesticide-degrading National Institute of Advanced Industrial Science coadaptation of pesticide-degrading bacteria to their hosts, enhancing increase and Technology).

1. de Bary A (1879) The Phenomenon of Symbiosis. (Ver- 8. Felsot AS (1989) Enhanced of insecti- 14. Simms EL, et al. (2006) An empirical test of partner lag Von Karl J. Trubner, Strasbourg). cides in soil: Implications for agroecosystems. Annu Rev choice mechanisms in a wild legume-rhizobium inter- 2. Haine ER (2008) Symbiont-mediated protection. Proc Entomol 34:453–476. action. Proc Biol Sci 273:77–81. Biol Sci 275:353–361. 9. Buchner P (1965) Endosymbiosis of Animals with Plant 15. Whalon ME, Mota-Sanchez D, Hollingsworth R (2008) 3. Werren JH, Baldo L, Clark ME (2008) Wolbachia: Master Microorganisms (Wiley Interscience, New York). Global Pesticide Resistance in Arthropods. (CAB Inter- manipulators of invertebrate biology. Nat Rev Micro- 10. Kikuchi Y, Hosokawa T, Fukatsu T (2011) An ancient national, Oxfordshire, UK). biol 6:741–751. but promiscuous host-symbiont association between 16. Saraswat S, Rai JPN (2011) Mechanism of metal toler- ance and detoxification in Mycorrhizal fungi. Bioma- 4. Moran NA (2007) Symbiosis as an adaptive process and Burkholderia gut symbionts and their heteropteran nagement Metal-Contaminated Soils 20:225–240. source of phenotypic complexity. Proc Natl Acad Sci hosts. ISME J 5:446–460. 17. Vanhaecke L, et al. (2008) Isolation and characteriza- USA 104(Suppl 1):8627–8633. 11. Kikuchi Y, Hosokawa T, Fukatsu T (2011) Specific de- tion of human intestinal bacteria capable of trans- 5. Kikuchi Y, et al. (2012) Symbiont-mediated velopmental window for establishment of an insect- forming the dietary 2-amino-1-methyl-6- – resistance. Proc Natl Acad Sci USA 109:8618 8622. microbe gut symbiosis. Appl Environ Microbiol 77: phenylimidazo[4,5-b]pyridine. Appl Environ Microbiol – 6. Mahenthiralingam E, Urban TA, Goldberg JB (2005) 4075 4081. 74:1469–1477. fi The multifarious, multireplicon Burkholderia cepacia 12. Haygood MG (1993) Light organ symbioses in shes. 18. Gill SR, et al. (2006) Metagenomic analysis of the hu- complex. Nat Rev Microbiol 3:144–156. Crit Rev Microbiol 19:191–216. man distal gut microbiome. Science 312:1355–1359. 7. Singh BK (2009) Organophosphorus-degrading bacte- 13. Little AF, van Oppen MJ, Willis BL, Willis BL (2004) Flex- 19. Dunning Hotopp JC, et al. (2007) Widespread lateral ria: Ecology and industrial applications. Nat Rev Micro- ibility in algal endosymbioses shapes growth in reef gene transfer from intracellular bacteria to multicellular biol 7:156–164. corals. Science 304:1492–1494. . Science 317:1753–1756.

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