The aim of this study was to investigate the effects of bioaugmentation with anaerobic rumen fungi at varied ratios of inoculums on the performance of anaerobic digesters of microalgae biomass for increasing methane production. Anaerobic rumen fungi, Anaeromyces, Neocallimastix, Orpinomyces and Piromyces, were used in this study and have groups of genes that originate from bacteria by the way of horizontal gene transfer. The results imply that rumen fungi improved the fermentation and degradation of microalgae biomass because they fostered cell wall degradation while methane production increased of 41% because of bioaugmentation with rumen fungi during anaerobic processes. Overall, the findings here indicate that bioaugmentation with a combination of rumen fungi in anaerobic process can represent an appropriate alternative to the use of chemical pre-treatments of microalgae biomass. Thus, anaerobic rumen fungi have promise for enhancing biogas production from different microalgae and macroalgae species and also various lignocellulosic substrates. (C) 2016 Elsevier B.V. All rights reserved.