ORIGINAL ARTICLE Reactive oxygen species production, induced by atmospheric modification, alter conidial quality of Beauveria bassiana D. P erez-Guzm an 1 , R. Montesinos-Mat  ıas 2 , O. Arce-Cervantes 3 , L.E. G omez-Quiroz 4 , O. Loera 5 and P.M. Garza-L  opez 3 1 Divisi  on de Ingenier  ıa Ambiental, Tecnol  ogico de Estudios Superiores del Oriente del Estado de M exico, La Paz, Estado de M exico, Mexico 2 Centro Nacional de Referencia de Control Biol  ogico, Tecom an, Colima, Mexico 3 Instituto de Ciencias Agropecuarias, Universidad Aut onoma del Estado de Hidalgo, Tulancingo, Hidalgo, Mexico 4 Departamento de Ciencias de la Salud, Universidad Aut onoma Metropolitana-Iztapalapa, M exico D.F., Mexico 5 Departamento de Biotecnolog  ıa, Universidad Aut onoma Metropolitana-Iztapalapa, M exico D.F., Mexico Keywords Beauveria bassiana, infectivity, oxygen pulses, quality, reactive oxygen species. Correspondence Paul Misael Garza-L opez, Instituto de Ciencias Agropecuarias, Universidad Aut onoma del Estado de Hidalgo, Avenida Universidad Km 1, Col. Ex-Hacienda de Aquetzalpa, Tulan- cingo, C.P. 43600 Hidalgo, M exico. E-mail: paul_garza@uaeh.edu.mx 2016/0098: received 12 January 2016, revised 4 April 2016 and accepted 20 April 2016 doi:10.1111/jam.13156 Abstract Aim: The aim of this study was to determine the relationship between reactive oxygen species (ROS) production and conidial infectivity in Beauveria bassiana. Methods and Results: Beauveria bassiana Bb 882.5 was cultured in solid-state culture (SSC) using rice under three oxygen conditions (21%, or pulses at 16 and 26%). Hydrophobicity was determined using exclusion phase assay. Bioassays with larvae or adults of Tenebrio molitor allowed the measurements of infectivity parameters. A fluorometric method was used for ROS quantification (superoxide and total peroxides). NADPH oxidase (NOX) activity was determined by specific inhibition. Conidial hydrophobicity decreased by O 2 pulses. Mortality of larvae was only achieved with conidia harvested from cultures under 21% O 2 ; whereas for adult insects, the infectivity parameters deteriorated in conidia obtained after pulses at 16 and 26% O 2 . At day 7, ROS production increased after 16 and 26% O 2 treatments. NOX activity induced ROS production at early stages of the culture. Conclusion: Modification of atmospheric oxygen increases ROS production, reducing conidial quality and infectivity. Significance and Impact of the Study: This is the first study in which conidial infectivity and ROS production in B. bassiana has been related, enhancing the knowledge of the effect of O 2 pulses in B. bassiana. Introduction The entomopathogenic fungus (EF) Beauveria bassiana is a widely used biological control agent, as an alternative for chemical insecticides, due to its wide host range and high specificity (Zimmermann 2007). Conidia are the most effi- cient infective units, which are mainly produced in solid- state culture (SSC) (Ye et al. 2006; Garza-L opez et al. 2012, 2015). Additionally, conidial adhesion to the insect cuticle is an important step in the infective cycle of EF, and occurs through unspecific interactions attributed to hydro- phobin-like proteins. Thus, it is important to determine quality parameters of any process to produce conidia (Jeffs et al. 1999; W€ osten 2001; Montesinos-Mat  ıas et al. 2011). Beauveria bassiana is an aerobic organism that pro- duces reactive oxygen species (ROS), such as superoxide anion and hydrogen peroxide, as a consequence of meta- bolic processes, mainly the respiratory chain or NADPH oxidases (NOX) activity (Aguirre et al. 2005). Cells have both enzymatic and nonenzymatic antioxidant defence mechanisms, which prevent biomolecule oxidation induced by ROS (Fridovich 1998; Aguirre et al. 2005). Furthermore, oxidative states promote cytodifferentiation in species belonging to Beauveria, Metarhizium and Journal of Applied Microbiology 121, 453--460 © 2016 The Society for Applied Microbiology 453 Journal of Applied Microbiology ISSN 1364-5072