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Two native Pleurotus spp. strains (white LB-050 and pale pink LB-051) were isolated from rotten tree trunks of cazahuate (Ipomoea murucoides) from the Mexican Mixtec Region. Both strains were chemically dedikaryotized to obtain their symmetrical monokaryotic components (neohaplonts). This was achieved employing homogenization time periods from 60 to 65 s, and 3 day incubation at 28 °C in a peptone-glucose solution (PGS). Pairing of compatible neohaplonts resulted in 56 hybrid strains which were classified into the four following hybrid types: (R1-nxB1-n, R1-nxB2-1, R2-nxB1-n and R2-nxB2-1). The mycelial growth of Pleurotus spp. monokaryotic and dikaryotic strains showed differences in texture (cottony or floccose), growth (scarce, regular or abundant), density (high, regular or low), and pigmentation (off-white, white or pale pink). To determine the rate and the amount of mycelium growth in malt extract agar at 28 °C, the diameter of the colony was measured every 24 h until the Petri dish was completely colonized. A linear model had the best fit to the mycelial growth kinetics. A direct relationship between mycelial morphology and growth rate was observed. Cottony mycelium presented significantly higher growth rates (p < 0.01) in comparison with floccose mycelium. Thus, mycelial morphology can be used as criterion to select which pairs must be used for optimizing compatible-mating studies. Hybrids resulting from cottony neohaplonts maintained the characteristically high growth rates of their parental strains with the hybrid R1-nxB1-n being faster than the latter.

Problem statement: Lactobacillus delbrueckii subsp. bulgaricus is a lactic bacteria mostly used in the production of yoghurt and it has an important probiotic activity that brings benefits to the human body. However, the gastrointestinal tract has aggressive conditions, such as the acid pH in the stomach and the bile in the duodenum, that reduce the viability of this bacteria. Approach: In order to evaluate the effect of the human gastrointestinal conditions on Lactobacillus delbrueckii's viability, a simulated in vitro gastrointestinal system was designed, which consisted of two reactors where stomach and human small intestine conditions were simulated. Results: Lactobacillus delbrueckii cells were treated in human gastric conditions simulated in vitro (gastric juice adjusted to pH 2, 37°C, 90 min and 50 rpm) and in intestinal conditions simulated in vitro (pancreatic juice adjusted to pH 6.8, 37°C, 150 min and 50 rpm) and in presence of a sample of food or beverages. A sample of typical Mexican food was added and at the end of the treatment 73% of the cells remained viable. This means 36.5 times more viability with respect to the cells treated under the same conditions in presence of a sample of milk with 8% starch. At the end of the treatment, the viability of cells treated in simulated in vitro gastrointestinal juices without sample of food or beverage (blank) was 1%. Conclusion: The results indicated that the in vitro simulated human gastrointestinal conditions were aggressive to the Lactobacillus delbrueckii's viability. To minimize this negative effect it is suggested that probiotics be consumed with some food because this could increase the probability that the bacteria reach the human colon in a large number and carry out their probiotic effect.

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