The interaction between bacteria and fungi on forage colonization in vitro

GILBERTO V. KOZLOSKI; DERICK C. RÖSLER; MARIANA P. MEZZOMO; CLAUDIO A. POZO

Florianópolis

Simposio; 11th International Symposium on the Nutrition of Herbivores; 2023

Forage degradation in the rumen occurs by attached microorganisms to plant cell walls, which chemical composition and histological structure are different in tropical compared to temperate grasses. Microorganisms probably interact with each other to degrade forage components whereas, however, the interactive role of fungi and bacteria in this process needs to be elucidated. Our objective was to evaluate the impact of antimicrobial substances on the level of bacteria and fungi attachment on residues of ryegrass and tifton-85 incubated in vitro. Dried and ground (1 mm screen) samples of ryegrass and tifton-85 were incubated in vitro for 24, 36 or 48 hours, in medium containing or not antimicrobial substances. A mixture of penicillin, chloramphenicol and streptomycin (500 mg/L of each) was used as antibiotic, and cycloheximide (50 mg/L) was used as an antifungal. Fermentations were conducted anaerobically in a water-bath slow-stir system (39°C). Treatments were antibiotic (Ab), antifungal (Af), negative control (without antimicrobials, C-) or positive control (with Ab and Af, C+). Three assays were conducted and, in each assay, three flasks per treatment were incubated. The content of each flask was mixed, filtered (nylon layer 40 um), washed with saline solution and DNA was extracted from residues and verified for its integrity (agarose gel) and concentration (by nanodrop equipment). The DNA of bacteria and fungi were quantified by qPCR analysis. Data were analyzed with a model that included the fixed effects of forage type, treatment, incubation time, their interactions and residual error. The means were compared using the student t test. In the C- treatment, as average of all incubation times, the DNA concentration (mg/g of residual dry matter) of both bacteria (0.207 vs 0.168) and fungi (0.053 vs 0.012) were higher (P < 0.05) in Tifton-85 than in ryegrass. For both forage types, the addition of Ab did not affect the concentration of fungi DNA whereas decreased (P < 0.05) about six times the concentration of bacterial DNA. The addition of Af almost eliminated all fungi DNA and, on average of both forage types and times of incubation, increased in 50% the concentration of bacterial DNA in residues. However, the positive impact of Af on bacterial DNA concentration in residues of ryegrass was observed in all incubation times whereas in residues of tifton-85 only at 36 and 48 hours of incubation. At 24 hours of incubation of Tifton-85, the Af showed a negative impact (P < 0.05) on bacterial DNA concentration. These results indicate that there is a competitive relationship between bacteria and fungi on colonizing particles of temperate grasses, or even tropical grasses at longer times of incubation. However, the presence of fungi seems to improve bacterial colonization of tropical grasses at the beginning of fermentative process.