No abstract

Biosurfactants are proteins with detergent, emulsifier, and antimicrobial actions that have potential application in environmental applications such as the treatment of organic pollutants and oil recovery. Bacillus atrophaeus strains are nonpathogenic and are suitable source of biosurfactants, among which is surfactin. The aim of this work is to establish a culture medium composition able to stimulate biosurfactants production by B. atrophaeus ATCC 9372. Batch cultivations were carried out in a rotary shaker at 150 rpm and 35 degrees C for 24 h on glucose-and/or casein-based semidefined culture media also containing sodium chloride, dibasic sodium phosphate, and soy flour. The addition of 14.0 g/L glucose in a culture medium containing 10.0 g/L of casein resulted in 17 times higher biosurfactant production (B(max)=635.0 mg/L). Besides, the simultaneous presence of digested casein (10.0 g/L), digested soy flour (3.0 g/L), and glucose (18.0 g/L) in the medium was responsible for a diauxic effect during cell growth. Once the diauxie started, the average biosurfactants concentration was 16.8% less than that observed before this phenomenon. The capability of B. atrophaeus strain to adapt its own metabolism to use several nutrients as energy sources and to preserve high levels of biosurfactants in the medium during the stationary phase is a promising feature for its possible application in biological treatments.

Twenty Holstein cows at 168 ± 87 d in milk (mean ± SD) were assigned to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement to evaluate the effects of 2 storage lengths (30 or 90 d) and the presence of sodium benzoate (control or 0.2% as fed) on the nutritive value of reconstituted sorghum grain silages (RSGS). For each treatment, dry ground sorghum grain was rehydrated to 35% moisture and ensiled in 200-L plastic drums. The treatments were RSGS stored for 30 d without sodium benzoate ( 30CON), RSGS stored for 30 d with sodium benzoate (30 BEN), RSGS stored for 90 d without sodium benzoate (90 CON) and RSGS stored for 90 d with sodium benzoate (90 BEN). Diets contained 16.3% RSGS. Silages stored for 90 d had higher concentrations of 1,2-propanediol, soluble protein, and ammonia nitrogen than did those stored for 30 d. Sodium benzoate reduced ethanol and ethyl-ester formation. Silages stored for 90 d had higher starch (89.3 vs. 86.9%) and protein (57.1 vs. 54.0%) digestibility compared with silages stored for 30 d. The ruminal acetate-to-propionate ratio tended to be lower in RSGS stored for 90 d than in RSGS stored for 30 d (3.75 vs. 3.34). Milk yield increased from 30.0 kg/d in cows fed RSGS stored for 30 d to 31.2 kg/d in cows fed RSGS stored for 90 d, without a change in dry matter intake (23.5 kg/d on average). Hence, feed efficiency and milk N efficiency also had tendencies to increase in cows fed RSGS stored for 90 d. Sodium benzoate did not alter cow performance but slightly increased plasma glucose (65.2 vs. 63.6 mg/dL). In conclusion, increasing the storage period of RSGS from 30 to 90 d improved starch and protein digestibility, milk yield, and feed efficiency.