Malt extract

The probiotic and yeast strain used in this study were Lactobacillus rhamnosus HN001 (Danisco A/S, Copenhagen, Denmark) and Saccharomyces cerevisiae EC-1118 (Lallemand Pty, Ontario, Canada), respectively.
Lactobacillus rhamnosus HN001 cells were grown by inoculating 1% (v/v) frozen stock culture into de Man, Rogosa, Sharpe (MRS) broth (Oxoid Ltd., Hampshire, England), followed by static incubation at 37 °C for 24 h. Yeast cells were propagated by inoculating 1% (v/v) frozen S. cerevisiae EC-1118 stock culture into yeast-malt (YM) broth (10 g/L dextrose (Sigma-Aldrich, Oakville, Ontario, Canada), 3 g/L yeast extract, 3 g/L malt extract and 5 g/L bacteriological peptone (all from Oxoid Ltd.), that was acidified to pH 5.0 with 1 M HCl and incubated statically at 30 °C for 24 h.
After two consecutive transfers, the microbial cultures were centrifuged (8000×g, 10 min, 4 °C) and washed twice with sterile 0.85% (w/v) NaCl. Working cultures were obtained by re-suspending the washed pellets to their initial volume with phosphate-buffered saline (PBS) that was acidified to pH 3.0 using 90% lactic acid (Merck, Darmstadt, Germany). All pH measurements were made using a Metrohm 713 pH meter (Herisau, Switzerland) calibrated with pH 4 and 7 buffers from Merck.

One non-oleaginous S. cerevisiae strain and five oleaginous yeast strains were used in this study. S. cerevisiae CEN.PK113-7D was kindly provided by Peter Kötter (Entian and Kötter 2007 (link)). Trichosporon oleaginosus DSM11815, Rhodotorula graminis DSM 27356, L. starkeyi DSM 70296, and R. toruloides DSM 70398 were purchased from the culture collection of the DSMZ (Braunschweig, Germany). Y. lipolytica CBS 6124 was purchased from the CBS-KNAW Fungal Biodiversity Centre (Utrecht, The Netherlands). Rich media, YPD or YM, were used for cultivation of these six yeasts. The YPD medium was prepared with 10 g/l yeast extract (Merck Millipore), 20 g/l peptone (Merck Millipore), and 20 g/l glucose (Merck Millipore). The YM medium was constituted of 3 g/l yeast extract (Merck Millipore), 3 g/l malt extract (Oxoid), 5 g/l peptone from soybeans (Merck Millipore), and 10 g/l glucose (Merck Millipore). The nitrogen-limited medium (named NLM medium in the text) was prepared as described in the literature using 70 g/l glucose (Merck Millipore) as carbon source (Yang et al. 2014 (link)).

In this study, strains belonging to seven different species were used. Pyricularia oryzae A2.5.2 (sensitive to strobilurins; WT) [29 (link)] and PO21_01 (resistant to strobilurins, RES), Penicillium expansum EM22, Mucor pyriformis EM14, Botrytis cinerea EM1, Fusarium culmorum FcUK [30 (link)], and F. graminearum ITA1601 [31 (link)] made a part of a fungal collection and were maintained in the laboratory of plant pathology of the University of Milan; Aspergillus niger ITEM9076 and ITEM9077 were obtained from the Agro-Food Microbial Culture Collection ITEM (Institute of Sciences of Food Production—ISPA, CNR, Bari, Italy). The strains were maintained as single-spore isolates on a malt-agar medium (MA: 20 g/L malt extract, Oxoid, UK; 15 g/L agar, Oxoid, UK) at 4 °C.