Identification of self inhibitory molecules in pathogenic mucorale Rhizopus arrhizus and evaluation of their potential therapeutic utility

Abstract

Rhizopus arrhizus is a saprophytic, pathogenic Mucoralean mold often associated with acute, highly aggressive and angioinvasive infections, namely mucormycosis. The major mode of dispersal of this mold is through sporangiospores, which germinate to form mycelia under suitable environmental conditions. In microbes, self-produced auto-regulatory molecules usually mediate such developmental decisions. However, the precise molecule(s) involved in this morphological transition in Mucorales have not been previously investigated. The present study has led to the identification of an indigenous volatile, quorum-based self-inhibitor namely 2-methyl-2-butene in R. arrhizus, which accumulated in dense cultures. The compound was found to inhibit R. arrhizus spore germination, growth, and biofilm formation. Furthermore, treatment of R. arrhizus spores with 2-methyl-2-butene led to the cytoskeletal alterations on fungal surface, such as filopodia formation, blebs, increased longitudinal folds and/or corrugations, and finger-like and sheet-like surface protrusions, depending upon the concentration and the planktonic or biofilm growth mode. Allied C5 derivatives, including 2-methyl-2-butanol, also partially mimicked the action of 2-methyl-2-butene by suppressing R. arrhizus spore germination and formation of filopodia-like and cytoneme-like structures. The same compound was also detected in another R. arrhizus strain (NCCPF 710427) and the Mucoralean species Rhizomucor pusillus (NCCPF 720004) and substantially impacted its spore germination as well. To our knowledge, the involvement of the quorum-driven molecule 2-methyl-2-butene in regulating the growth and biofilm formation of R. arrhizus has not been previously reported. newline