*3.1. Strategies for Development Ideal Consolidated Bioprocessing-Enabling Microorganisms*

In searching for CBP functional organism, two different strategies have been applied to endow the microorganism with the capabilities required, such as high hydrolysis rate, tolerance to a compound derived from pretreatment, and proper fermentation.

## 3.1.1. Native Strategy

The native strategy focuses on studying organisms with the natural capacity to produce different enzymes and use different substrates to improve biofuels' performance. Some approaches to enhance bioprocessing capabilities include adaptive evolution and isolation of new strains for CBP [55].

The native strains proposed for use in CBP are mainly wild-type strains that are generally poorly characterized. To date, genetic manipulation tools are established for only some of them, and in a few cases, their metabolisms are investigated in-depth. Concerning cellulolytic fungi, most genetic engineering efforts are focused on increasing cellulase production. However, there is a growing interest in biofuel production using these organisms. Candidates for the native strategy can be classified into three groups: fungi, bacteria that produce and excrete enzymes, and cellulosome-forming bacteria [56–58].

However, to date, the organisms discovered with the capacity to carry out CBP are well below efficient alcohol production expectations. Therefore, the co-cultivation of two or more different organisms (consortium) taking advantage of their capacities-specific metabolism is a promising method to improve substrate conversion and ethanol yield [56]. A microbial consortium is an association of two or more organisms acting together as a community in a complex system, where all benefits from others' activities can be enjoyed [59]. Consortia can be classified into natural, artificial, and synthetic. Natural consortia are symbiotic due to co-evolution; in contrast, artificial consortia and synthetic

consortia are defined as mixed crop systems, differing from each other. In synthetic consortia, genetic modifications are performed to achieve specific interactions between mixed strains [60].
