Current Biotechnology Send Orders for Reprints to reprints@benthamscience.ae Current Biotechnology, 2018, 7, 65-69 65 RESEARCH ARTICLE Conidia Production of Metarhizium anisopliae in Bags and Packed Column Bioreactors Fernando Méndez-González 1,3 , Octavio Loera 2 and Ernesto Favela-Torres 2,* 1 Departamento de Producción Agrícola y Animal, Universidad Autónoma Metropolitana, Unidad Xochimilco, 04960 México City, Mexico; 2 Departamento de Biotecnología, Universidad Autónoma Metropolitana, Unidad Iztapalapa, 09340 Mexico, México and 3 División de Ingeniería Química, Tecnológico Nacional de México, Campus Chimalhuacán, 56330 Mexico City, México Abstract: Background: Metarhizium anisopliae controls insect pest populations and commercial formulations are based on conidia, regularly produced in plastic bags using rice grains as substrate. This process is la- bour-intensive and difficult to control; optimisation represents a current problem, even using different types of bioreactors. However, comparisons between Metarhizium conidia production in bags and packed columns are scarce. Objective: The aim of this study was to evaluate the age of the inoculum and two different type of bio- reactors on the production of conidia from Metarhizium anisopliae. Method: Metarhizium anisopliae strain CP-OAX was used for conidia production (inoculum of 19 or 25 days old) using steamed rice as substrate either in plastic bags or packed bed bioreactors, the latter with different sizes with air supply. Results: Up to 30% higher conidia yields were obtained in the packed bed bioreactor after 7 days, using a 25 days old inoculum. Respirometric analysis on the packed bed bioreactor determined lag values from 49.08 to 55.23 h and maximum CO2 production rate of 0.295 ± 0.015 mg gidm -1 h -1 ; maximum sporulation occurred at 56.7 h. Conclusion: Both inoculum age and bioreactor geometry affect conidia production and productivity. The packed column bioreactor allowed higher conidia production and productivity. Air supply at the high scale packed column bioreactor allows metabolic heat removal to maintain isothermal conditions. In addition, the packed bed bioreactor presents advantages, such as reproducibility, the possibility of scaling-up and monitoring the process in terms of temperature and CO2 production. A R T I C L E H I S T O R Y Received: June 16, 2016 Revised: September 5, 2016 Accepted: September 21, 2016 DOI: 10.2174/2211550105666160926123350 Keywords: Metarhizium anisopliae, conidia production, solid-state fermentation, biological control, bioreactor, respirometric analysis. 1. INTRODUCTION Organisms used in biological control include entomopatho- genic fungi of the genus Metarhizium, which is one of the most widely used biopesticide [1] and infects insects of different orders [2-4]. The conidia of these fungi are able to adhere to insects by hydrophobic interactions between insect epicuticle and fungal cell wall [5]; then conidia germinate and fungal penetration into the insect begin [6], degrading the main com- ponents of the insect cuticle with a battery of enzymes [7, 8]. The infection process ends with insect colonization and death. Commercial formulations of Metarhizium sp. are pre- pared with conidia [9] produced by solid-state fermentation [10]. Conidia production is performed in plastic bags with a *Address correspondence to this author at the Departamento de Bio- tecnología, Universidad Autónoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Col. Vicentina, C, P. 09340, Ciudad de México, México; Tel: 525558046555; Fax 525558044711; E-mail: favela@xanum.uam.mx capacity of 1 kg of rice, with a fermentation time from 8 to 13 days [11]. The procedure has few control parameters and requires intensive labor; therefore, the design of a controlled process with high conidia yields is a current challenge in bioinsecti- cide production. The use of large scale aerated bioreactors could contribute to this problem. In fact, several studies have evaluated the effects of soil medium composition, water ac- tivity, packing density, temperature gradient and forced and passive aeration on conidia production [10, 12-14], however, comparisons between Metarhizium sp. conidia production in bags and packed columns in terms of respirometric analysis are scarce. The aim of this work was to determine the effect of the bioreactor geometry on the conidia production of Metharizi- um anisopliae. For that, we evaluated conidia plastic bags (traditional cultivation) and packed columns. Respirometric 2211-551X/18 $58.00+.00 © 2018 Bentham Science Publishers