Complex sentence: One study showed that MHB aided in colonization of a type of fungal pathogen because the surrounding environment was not suitable for the symbiotic mycorrhiza, thus the MHB became more harmful under certain conditions to increase their own fitness.
Split into simpler sentences: One study showed that MHB aided in colonization of a type of fungal pathogen because the surrounding environment was not suitable for the symbiotic mycorrhiza. Thus the MHB became more harmful under certain conditions to increase their own fitness.