Enzymes of early-diverging, zoosporic fungi

Abstract

The secretome, the complement of extracellular proteins, is a reflection of the interaction of an organism with its host or substrate, thus a determining factor for the organism’s fitness and competitiveness. Hence, the secretome impacts speciation and organismal evolution. The zoosporic Chytridiomycota , Blastocladiomycota , Neocallimastigomycota , and Cryptomycota represent the earliest diverging lineages of the Fungal Kingdom. The review describes the enzyme compositions of these zoosporic fungi, underscoring the enzymes involved in biomass degradation. The review connects the lifestyle and substrate affinities of the zoosporic fungi to the secretome composition by examining both classical phenotypic investigations and molecular/genomic-based studies. The carbohydrate-active enzyme profiles of 19 genome-sequenced species are summarized. Emphasis is given to recent advances in understanding the functional role of rumen fungi, the basis for the devastating chytridiomycosis, and the structure of fungal cellulosome. The approach taken by the review enables comparison of the secretome enzyme composition of anaerobic versus aerobic early-diverging fungi and comparison of enzyme portfolio of specialized parasites, pathogens, and saprotrophs. Early-diverging fungi digest most major types of biopolymers: cellulose, hemicellulose, pectin, chitin, and keratin. It is thus to be expected that early-diverging fungi in its entirety represents a rich and diverse pool of secreted, metabolic enzymes. The review presents the methods used for enzyme discovery, the diversity of enzymes found, the status and outlook for recombinant production, and the potential for applications. Comparative studies on the composition of secretome enzymes of early-diverging fungi would contribute to unraveling the basal lineages of fungi.

Evolution of Fungal Carbohydrate-Active Enzyme Portfolios and Adaptation to Plant Cell-Wall Polymers

“…The cell walls of streptophyte algae contained cellulose, xyloglucans, and pectin, but lacked lignin [ 27 ]. On their side, early diverging fungi that lived in association with streptophytes possessed cellulase, xyloglucanase, and pectinase genes in their genome, indicating that these enzymes were part of the ancestral fungal toolkit for breaking down plant material ( Figure 1 a) [ 24 , 25 , 26 , 28 ]. Later, pectinase genes were convergently lost in lineages that adopted a nonstreptophyte nutrition, whereas organisms that had adopted a plant-based nutrition were under continuous selection pressure to retain pectinase genes [ 29 ].…”

Chytrid fungi shape bacterial communities on model particulate organic matter

“…Once attached, a zoospore loses its flagellum before developing a walled sporangium with a rhizoid network, which attaches to and penetrates the substrate [27]. Chytrids subsequently feed saprotrophically via the rhizoids, which secrete extracellular enzymes to degrade POM to low molecular weight substrates for uptake and assimilation [28].…”

New Method for Identifying Fungal Kingdom Enzyme Hotspots from Genome Sequences

“…The exceptionally high “Function;Family” observation scoring of rumen fungi ( P. ruminatium and N. californiae (Neocallimastigomycetes)) reflects that the genomes of these organisms encode for a very high number of cellulose and xylan degrading enzymes in accord with the types of substrates the fungi encounter in the cow’s rumen [ 21 ]. In addition, the high scores may also reflect that these highly specialized early diverging, anaerobic fungi have a unique genome organization (including numerous duplications) and a similarly unique enzyme cellulosome structure [ 22 , 23 ].…”