Pectinases in Leaf Degradation by Aquatic Hyphomycetes: the Enzymes and Leaf Maceration

Abstract

All seven species of aquatic hyphomycetes tested produced both polygalacturonases and pectin lyases. The polygalacturonases were constitutive, whereas the pectin lyases were induced on pectic substrates at pH 6.5 and above. Some species could grow on pectic substrates at both pH 5 and pH 7; other species at pH7 only. Tricladium splendens grew as well on a polypectate substrate as it did on glucose. This fungus elaborated three endo-polygalacturonase isoenzymes, as did Articulospora tetracladia. Tetrachaetum elegans secreted a presumed exo-pectin lyase and a pectin esterase, and Mycocentrospora angulata an endo-pectin lyase and a pectin esterase. The four species macerated alder-leaf strips totally within 9 to 12 d at stream pH 7, utilizing predominantly pectin lyases and pectin esterases. These enzymes are stimulated by Ca2+, and this may explain why plant decay proceeds most rapidly in calcium-rich streams of pH 6.5 and above. The frequency with which the four species of aquatic hyphomycetes were observed on experimental leaf packs placed in a stream does not appear to be related to their pectolytic capability. METHODS Fungi and culture media. The following species of aquatic hyphomycetes were isolated from scum samples taken from the River Bourne (Chamier & Dixon, 1982): Articulospora tetracladia Ingold, Lemonniera aquatica de Wild.

Influence of pH on the growth and leaf-maceration ability of fungi involved in the decomposition of floating leaves of Nymphaea alba in an acid water

“…These results support the findings of Chamier & Dixon (1982b), who found that of seven species of aquatic Hyphomycetes investigated, only two grew well on polypectate agar at pH 5, whereas all species did so at pH 7. The fungi used in our investigation were somewhat more acid-tolerant, possibly because of a selection in an acidic environment.…”

“…These authors suggested that this was due to inhibition of the breakdown of cell wall components. Chamier & Dixon (1982b) showed that pectin degradation and leaf maceration by selected aquatic Hyphomycetes was inhibited at pH < 5 . Pectate lyase, an important enzyme in tissue maceration (Friend, 1977, and references therein) was not found in cultures grown at pH <6-5.…”

Attraction of the amphipod Gammarus pulex to water-borne cues of food

“…Our findings are consistent with other observations that all showed a preference of Gammarus to fungi-conditioned leaves (Ba¨rlocher & Kendrick, 1975;Sutcliffe et al, 1981;Grac¸a et al, 1993a). This preference is explained from the presence of aquatic hyphomycetes that degrade the pectic polymers in leaf cell walls (Chamier & Dixon, 1982). These hyphomycetes breakdown leaf tissue, making it easier for Gammarus to consume and allowing for a faster overall consumption rate (Sutcliffe et al, 1981).…”

Effect of experimental and seasonal warming on litter decomposition in a temperate stream

“…Microbes, aquatic hyphomycetes in particular, macerate the leaf matrix by the activities of extracellular enzymes (Chamier and Dixon 1982), convert organic carbon into fungal biomass (mycelium and conidia; Gessner and Chauvet 1994;Gulis and Suberkropp 2003;Ferreira et al 2012), and mineralize it (Gulis and Suberkropp 2003), which leads to litter mass loss (Hieber and Gessner 2002). The accumulation of fungal biomass and the maceration of litter increase the litter quality for invertebrate detritivores, whose feeding activities lead to further litter mass loss (Bärlocher and Kendrick 1975;Graça et al 2001;Chung and Suberkropp 2009).…”