Brazilian Bioluminescent Beetles: Reflections on Catching Glimpses of Light in the Atlantic Forest and Cerrado

Anais da Academia Brasileira de Ciências (2018) 90(1 Suppl. 1): 663-679 (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 http://dx.doi.org/10.1590/0001-3765201820170504 www.scielo.br/aabc | www.fb.com/aabcjournal Brazilian Bioluminescent Beetles: Reflections on Catching Glimpses of Light in the Atlantic Forest and Cerrado ETELVINO J.H. BECHARA and CASSIUS V. STEVANI Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-000 São Paulo, SP, Brazil Manuscript received on July 4, 2017; accepted for publication on August 11, 2017 ABSTRACT Bioluminescence - visible and cold light emission by living organisms - is a worldwide phenomenon, reported in terrestrial and marine environments since ancient times. Light emission from microorganisms, fungi, plants and animals may have arisen as an evolutionary response against oxygen toxicity and was appropriated for sexual attraction, predation, aposematism, and camouflage. Light emission results from the oxidation of a substrate, luciferin, by molecular oxygen, catalyzed by a luciferase, producing oxyluciferin in the excited singlet state, which decays to the ground state by fluorescence emission. Brazilian Atlantic forests and Cerrados are rich in luminescent beetles, which produce the same luciferin but slightly mutated luciferases, which result in distinct color emissions from green to red depending on the species. This review focuses on chemical and biological aspects of Brazilian luminescent beetles (Coleoptera) belonging to the Lampyridae (fireflies), Elateridae (click-beetles), and Phengodidae (railroad-worms) families. The ATPdependent mechanism of bioluminescence, the role of luciferase tuning the color of light emission, the “luminous termite mounds” in Central Brazil, the cooperative roles of luciferase and superoxide dismutase against oxygen toxicity, and the hypothesis on the evolutionary origin of luciferases are highlighted. Finally, we point out analytical uses of beetle bioluminescence for biological, clinical, environmental, and industrial samples. Key words: Coleoptera, bioluminescence, luciferase, luciferin, luminous termitary, oxidative stress. INTRODUCTION Bioluminescence is defined as visible and cold light emission by living organisms. It results from the oxidation of a substrate called luciferin by molecular oxygen catalyzed by an enzyme named luciferase, leading to a singlet excited-state product Correspondence to: Etelvino José Henriques Bechara E-mail: * Contribution to the centenary of the Brazilian Academy of Sciences. (oxyluciferin*), which decays to the ground state emitting fluorescence (Shimomura 2012, Wilson and Hastings 2013). Thus, bioluminescence results from conversion of chemical energy into photons: Luciferin + O2 (luciferase) → Oxyluciferin* → Oxyluciferin + Light This review concerns about 30 years of investigation on several species of Brazilian bioluminescent beetles (Coleoptera), mainly An Acad Bras Cienc (2018) 90 (1 Suppl. 1) 664 ETELVINO J.H. BECHARA and CASSIUS V. STEVANI click-beetles (Elateridae) and railroad-worms (Phengodidae) found in the Brazilian Atlantic Forest and the Cerrado biome. During the rainy season, after sunset, bright and multicolored light flashes emitted by flying beetles (Coleoptera) offer a magnificent visual spectacle (Bechara 1988, Bechara and Viviani 2015). Not surprisingly, how and why these worldwide distributed insects emanate intense and cold light are questions that have awakened the curiosity of ordinary people, writers, philosophers and scientists since ancient times (Harvey 1957). Impressed by the intense flashes of light sparked by the firefly at night, Machado de Assis, a renowned Brazilian writer wrote the sonnet Círculo Vicioso (Vicious Circle) where a whispering chain of firefly, star, moon, and the sun envy the brighter one, and finally the sun, feeling itself too radiant and hot, wishes to be a simple firefly. The sonnet ‘jealous’ insect aspires to be able to chemically produce as much energy as the nuclear forces of the stars, being orders of magnitude higher. Dancing in the air, moaned a restless firefly: “Oh, would that I could be that star so yellow Shining in the everlasting blue, as a candle mellow!” But the star gazed at the moon with envy high: “If only I could copy thy wondrous silver light, That from column Greek to Gothic window-case Hath gazed with longing on my beloved’s face!” Yet the moon turned to the sun, full of spite: “Wretch! I would have thy clarity overwhelming Shining immortal, all light joined in one!” Replied the Sun, his shining crown bending: “Weary am I of this halo of luminous sky This light and boundless canopy weighs heavy. Oh, that I were born a humble firefly!” Vicious Circle, Machado de Assis (Courtesy free translation by Clara Allain) In fact, an attentive onlooker would soon realize that the beetles, swirling in their glimmering cloud, are caught up in their nuptial flight. Afterwards, the insects pose on leaves and grass for copulation. In Brazil, the occurrence of fireflies and other luminous insects was first registered by Gabriel de Souza in 1587 in a document to Felipe I, King of Portugal and Spain, describing “mamoás” (fireflies) and “buijejas” (probably, railroad-worms) so called by the Amerindians of the State of Bahia (Moraes 1940). Fireflies (Lampyridae), click-beetles (Elateridae) and railroad-worms (Phengodidae) constitute the three most abundant families of luminescent coleopterans in Brazil (Fig. 1). Until present days, elucidation of the biochemical mechanism of a given luminescent organism, be it a fly (Viviani et al. 2002) or a mushroom (Oliveira and Stevani 2009), frequently employs the preparation of a “hot” extract by heatinduced enzyme denaturation: the initial step of the basic protocol long established by Raphael Dubois Figure 1 - Photographs of a firefly (Macrolampis omissa) (a), a click-beetle (Pyrophorus sp.) (b), and a railroad-worm (Phrixothrix hirtus) (c). An Acad Bras Cienc (2018) 90 (1 Suppl. 1) CHEMISTRY AND BIOLOGY OF BEETLE BIOLUMINESCENCE (1886) when studying the basic ingredients for light emission by a click-beetle, formerly named Pyrophorus noctilucus. Dubois mixed “cold” and “hot” aqueous extracts of the insect lanterns and discovered that a thermostable substrate (luciferin) and a thermolabile component (luciferase) elicit a flash of green light. Much later, McElroy (1947) discovered that addition of ATP and Mg2+ ions is also necessary to enhance the in vitro and in vivo firefly bioluminescence. Success of the Dubois experiment with any bioluminescent organism also depends on molecular oxygen, a requirement discovered by Robert Boyle (1668a, b) when comparing the luminescence of decomposing fish (actually bacteria) and rotten wood (from saprophytic fungi) under ‘vaccum’ (sic) and air. He also differed the nature of the flame of bu (...truncated)