The Role of Hydrophobicity and Surface Receptors at Hyphae of Lyophyllum sp. Strain Karsten in the Interaction with Burkholderia terrae BS001 - Implications for Interactions in Soil

The soil bacterium Burkholderia terrae strain BS001 can interact with varying soil fungi, using mechanisms that range from the utilization of carbon/energy sources such as glycerol to the ability to reach novel territories in soil via co-migration with growing fungal mycelia. Here, we investigate the intrinsic properties of the B. terrae BS001 interaction with the basidiomycetous soil fungus Lyophyllum sp. strain Karsten. In some experiments, the ascomycetous Trichoderma asperellum 302 was also used. The hyphae of Lyophyllum sp. strain Karsten were largely hydrophilic on water-containing media versus hydrophobic when aerial, as evidenced by contact angle analyses (CA). Co-migration of B. terrae strain BS001 cells with the hyphae of the two fungi occurred preferentially along the - presumably hydrophilic - soil-dwelling hyphae, whereas aerial hyphae did not allow efficient migration, due to reduced thickness of their surrounding mucous films. Moreover, the cell numbers over the length of the hyphae in soil showed an uneven distribution, i.e., the CFU numbers increased from minima at the inoculation point to maximal numbers in the middle of the extended hyphae, then decreasing toward the terminal side. Microscopic analyses of the strain BS001 associations with the Lyophyllum sp. strain Karsten hyphae in the microcosms confirmed the presence of B. terrae BS001 cells on the mucous matter that was present at the hyphal surfaces of the fungi used. Cell agglomerates were found to accumulate at defined sites on the hyphal surfaces, which were coined ‘fungal-interactive’ hot spots. Evidence was further obtained for the contention that receptors for a physical bacterium-fungus interaction occur at the Lyophyllum sp. strain Karsten hyphal surface, in which the specific glycosphingolipid ceramide monohexoside (CMH) plays an important role. Thus, bacterial adherence may be mediated by heterogeneously distributed fungal-specific receptors, implying the CMH moieties. This study sheds light on the physical aspects of the B. terrae BS001 – Lyophyllum sp. strain Karsten interaction, highlighting heterogeneity along the hyphae with respect to hydrophobicity and the presence of potential anchoring sites.

Structural analysis of glucosylceramides (GlcCer) from species of the Pseudallescheria/Scedosporium complex

Glucosylceramides (GlcCer) are the main neutral glycosphingolipids expressed in fungal cells. In this work, glucosylceramides (GlcCer) were extracted from three strains of Scedosporium (Pseudallescheria) boydii, one strain of Pseudallescheria ellipsoidea and one strain of Pseudallescheria angusta and purified by several chromatographic steps. Using high-performance thin layer chromatography (HPTLC), we found a similarity between GlcCer obtained from all of the analysed strains. A detailed structural analysis of the P. ellipsoidea GlcCer was performed via electrospray ionization mass spectrometry (ESI-MS) and confirmed in 1- and 2-D heteronuclear NMR experiments ((1)H-(13) C HSQC). GlcCer species produced by mycelial forms of these strains displayed the same structure previously demonstrated by our group for P. boydii, Cryptococcus neoformans, Pseudallescheria minustipora, Fusarium solani, and Colletotrichum gloesporioides. A monoclonal antibody (mAb) against GlcCer was used for immunofluorescence experiments. Our results revealed that GlcCer is present on the surface of these fungi, and no difference was observed in the GlcCer structure of the present set of strains in terms of geographic or clinical origin, suggesting a conserved GlcCer structure similar to those previously described for Scedosporium apiospermum, Scedosporium aurantiacum, and P. minutispora. The surface distribution of GlcCer in these fungi is suggestive of the involvement of this molecule in fungal growth.