Fatty Acid methyl ester profiles for characterization of glomalean fungi and their endomycorrhizae

Abstract

Arbuscule-forming fungi in the order Glomales form obligate endomycorrhizal associations with plants that make them difficult to quantify, and taxonomy of the group is only beginning to be objectively understood. Fatty acid methyl ester (FAME) profiles were analyzed to assess the diversity and quantity of fatty acids in 53 isolates of 24 glomalean species. Spores and endomycorrhizal roots of sudan grass (Sorghum sudanense) and the citrus rootstock Carrizo citrange (Poncirus trifoliata ؋ Citrus sinensis) were examined. Spores yielded reproducible FAME profiles from replicate spore collections extracted from soil pot cultures despite being grown in association with a host plant and with contaminating microorganisms present. Unweighted pair group analysis revealed relatively tight clusters of groups at the intraspecific, specific, and generic levels; however, lipid profiles at the family level were convergent. Thus, FAME profile comparisons provided a robust measure of similarity below the family level. FAME profiles in sudan grass roots containing vesicles and/or spores of Glomus intraradices were more similar to spore profiles than to profiles from nonmycorrhizal roots. The FAME profiles for Gigaspora species, which do not form vesicles or spores in roots, were less distinct from nonmycorrhizal roots. G. intraradices and G. rosea produced fatty acids in roots that were distinguishable from each other as well as from the host root. Production in citrus roots of the fatty acid 16:1 5 cis by two Glomus species was correlated with the development of mycorrhizal colonization as measured by clearing and staining procedures and by estimates of total incidence and vesicle intensity. FAME analysis of roots not only provided a measure of colonization development but also served as an index of carbon allocated to intraradical fungal growth and lipid storage.

Tracking carbon from the atmosphere to the rhizosphere

“…AM fungal neutral lipids are usually stored in intraradical vesicles or in spores and make up a large proportion of the AM fungal biomass (Olsson & Johansen 2000;Bago et al 2002;Olsson et al 2002). In G. intraradices, 50-70% of the neutral lipids are the fatty acid 16 : 1x5 (Graham et al 1995;Olsson & Johansen 2000;Olsson et al 2002). Dynamics of this compound in our experimental system indicates that the C assimilated by AM fungi resides for much longer than 5-6 days, probably in intraradical vesicles and in intra-and extraradical spores.…”

“…Neutral lipid fatty acid 16 : 1x5 is a sensitive signature of AM fungi in both roots and soil (Graham et al 1995;Olsson et al 1995). PLFA 16 : 1x5 is a constituent of AM fungal membranes, with rather low specificity as a signature because of relatively low content in AM fungi and a high background in soil originating from bacteria (Olsson et al 1995).…”

Soil microbial community structure and enzymatic activity responses to nitrogen management and landscape positions in switchgrass (Panicum virgatumL.)

“…The 16:0 10-methyl, 17:0 10-methyl, 18:0 10-methyl are classified as actinomycetes biomarkers. The 16:1w5 and 20:4w6 are biomarkers for arbuscular mycorrhizal (AM) fungi (Graham, Hodge, & Morton, 1995), and 18:3w3, c18:2w9,12 and c18:1w9 are biomarkers for saprotrophic fungi (Zelles, 1999). We grouped the 16:0 fatty acid (Zelles, 1999) and the general bacterial indicators 14:0, 15:0, 17:0 and 18:0 as universal PLFA biomarkers (Frostegård, Tunlid, & Bååth, 2011;Zelles, 1999).…”

Phylogeny of arbuscular mycorrhizal fungi predicts community composition of symbiosis-associated bacteria

“…Altered bacterial communities may be a direct consequence of either the tissue quality and/or quantity of arbuscular mycorrhizal fungal hyphae and spores (Figs 3 and 4). Examples of different biochemical quality of arbuscular mycorrhizal fungal mycelia from different species include differential content of the recalcitrant proteinaceous substance glomalin (Wright & Upadhyaya, 1998) or of fatty acids (Graham et al, 1995). In addition to direct nutritional effects, direct biotic interaction of arbuscular mycorrhizal fungal mycelia and bacterial populations, for example through fungal production of stimulatory or inhibitory compounds, may also have contributed to the observed effect.…”