Psychrotolerant mucoralean fungi present in pristine mountain fynbos soil and vineyard soil from the Stellenbosch region

[摘要] ENGLISH ABSTRACT:Mucoralean fungi are mostly saprotrophs that are frequently encountered in soilhabitats. Using an isolation temperature of circa 25°C, other workers obtainedthese fungi from a wide diversity of geographical areas in southern Africa.However, it is known that psychrotolerant mucoralean fungi, able to grow at25°C as well as at 5°C, occur in pristine Alti Mountain Grassland. Nothing isknown about the diversity of these psychrotolerant soil fungi in other vegetationtypes of South Africa.Consequently, in this study, the psychrotolerant fungal taxa and numbers in soilfrom a vineyard and from pristine Mountain Fynbos were determined using anincubation temperature of 4°C and a complex isolation medium. The lattercontained agar, malt extract, peptone, yeast extract, penicillin and streptomycinsulphate. Soil samples were analysed in late summer, autumn and mid-winter.It was found that, for the samples taken in late summer and autumn, thediversity of mucoralean species in the soil differed between fynbos andvineyard. In winter however, no significant difference was detected between theShannon's diversity indices of mucoralean species in the soil samples takenfrom the two habitats. It was found that in both soil types, the percentagemucoralean fungi on the plates increased from summer to winter. In addition,the numbers of detectable Morlierella subgenus Morlierella on the plates werehigher in winter than in late summer. The diversity of mucoralean speciesobtained during winter in fynbos and vineyard soil was significantly less than thediversity of these species in Alti Mountain Grassland soil.To determine if the Morlierella subgenus Morlierella isolates from the fynbosand vineyard soil, and those obtained from Alti Mountain Grassland, differ in theability to grow at low temperatures, the radial growth rate on malt extract agar at4°C and BOC was determined for each isolate. The results indicate that not onlydid seasonal changes occur in the taxa within Morlierella subgenus Morlierella,but that the isolates dominating the soil in different seasons also differed in theability to grow at low temperatures. The percentage of isolates that hadreached greater colony diameters after B days of incubation at 4°C, was higher for the isolates obtained in the cold wet month of July than for those obtained inthe warmer dryer month of February. Similar results were obtained with theradial growth experiments conducted at BOC. The Morlierella subgenusMorlierella isolates obtained in winter from fynbos and vineyard soil showedless variation in low temperature growth rate than the isolates of this taxonobtained in winter from Alti Mountain Grassland soil during a previous study.This variation corresponds to the greater number (20) of Morlierella subgenusMorlierella species found in the grassland soil. Altogether only seven speciesof this subgenus was detected during the present study in the fynbos andvineyard soil samples. It was speculated that this difference in diversitybetween the fynbos and vineyard isolates, and the grassland isolates obtainedin a previous study, might have been as a result of differences in the habitat orthe enumeration methods used.The phylogenetic relationship between different psychrotolerant isolates ofMorlierella subgenus Morlierella originating from the soil of the fynbos, vineyardand Alti Mountain Grassland, was subsequently determine through comparisonof ITS regions, within ribosomal RNA repeats. Consequently, 45psychrotolerant Morlierella subgenus Morlierella isolates originating from thethree soil habitats was compared on the basis ITS 1 nucleotide sequencecomposition and radial growth rate at 4°C. Phylogenetic analyses showed thatthe isolates could be grouped into two clusters correlating with the ability togrow at low temperatures. Each cluster was further subdivided into twosubgroups. It was found that except for one subgroup and the reference strainoccurring in another subgroup, all the subgroups contain isolates originatingfrom a single soil habitat. Therefore, the ITS 1 sequence of these fungi seemsto indicate the original habitat and ability to grow at low temperatures. Thiscorrelation of the ITS sequence with the ecological habitat of a fungus has alsobeen observed by other workers for other fungal groups.

[发布机构] Stellenbosch University