Ultrasound conditioning of Streptococcus thermophilus CNRZ 447: growth, biofilm formation, exopolysaccharide production, and cell membrane permeability

Sonication is one of the new and innovative approaches that is being increasingly used in food industry to control fermentation processes and to eradicate spoiling. Recently, this approach has seen new industrial applications such as enhancing microbial productivity. The present study aimed to assess the effects of ultrasound conditioning on the metabolism and extracellular matrix production of Streptococcus thermophilus. Bacterial suspensions were treated in ultrasonic bath (35 kHz, 240/60 W peak/nominal power, 1.8 l capacity) for different time periods (5, 10, 15, 20, 30, 45, and 65 min), and the growth improvement, adhesion ability, biofilm formation, and exopolysaccharide production of the bacterial strain were measured. The bacterial strain exhibited resistance to the treatment, and the conditioning improved the growth, adhesion, membrane permeability, biofilm formation, and exopolysaccharide production ability. An optimal treatment was obtained for 30 minutes of conditioning. An excellent yield of desirable exopolysaccharides (1788 mg glucose equivalent/l) was achieved. Ultrasound conditioning may be used as a potential approach to enhance certain biotechnological properties of industrial microorganisms.