Hidrolisado ácido-térmico da macroalga marinha Solieria filiformis (Kützing) P.W. Gabrielson como meio nutritivo para o crescimento da bactéria Bacillus clausii

Abstract

Red macroalgae have a chemical composition rich in total carbohydrates, such as galactans and cellulose, proteins, and mineral salts, with a biomass that is easily hydrolyzed compared to lignocellulosic materials. Thus, they can constitute a new source of nutrients for the growth of microorganisms used in industry. In this context, the objective of the present study was to evaluate the potential of the acid-thermal hydrolysate of the red macroalga Solieria filiformis as a nutritional medium for the growth of the bacteria Bacillus clausii. Initially, the marine macroalga S. filiformis was collected at Flecheiras beach, in the municipality of Trairí-CE. The hydrolysis of the biomass was performed at a concentration of 0.5 M of acid solution, 121 °C, and 1 atm. Subsequently, the levels of reducing sugars (RS), total carbohydrates (TC), and soluble proteins (SP) were determined. Then, the growth curves of B. clausii were obtained in standard nutrient broth and in the hydrolysate at a concentration of 10 g/L of reducing sugars, 37 °C, and 150 rpm for 48 hours in an incubator with orbital shaking. Aliquots of 2 mL were taken every 2 hours during fermentation to determine optical density (600 nm) and viable cell counts on plates, and the kinetic parameters of bacterial growth were calculated. The concentration of RS in the hydrolysate was 15.53 g/L, TC was 19.87 g/L, and SP was 0.30 mg/mL. Due to the low protein content, the hydrolysate was supplemented with peptone (5.0 g/L). The growth curves of B. clausii showed similar profiles in both media, exhibiting comparable times for the Lag, Log, Stationary, and Decline phases, respectively 0, 10, 4, and 34 hours for the standard medium, and 0, 5, 15, and 4 hours for the hydrolysate. Thus, a maximum cell concentration of 3.9 x 10^10 CFU/mL and 1.99 x 10^8 for the standard medium and hydrolysate, respectively, was obtained. Themaximum growth rate (µmax) and generation time (g) were 0.14 h^-1 and 85.80 min for the standard medium, and 0.10 h^-1 and 46.2 min for the hydrolysate. Therefore, the acidthermal hydrolysate of the marine macroalga S. filiformis shows potential as a culture medium rich in RS but with a low protein content. With the obtained results, further research can be conducted to confirm its use as a complex culture medium for bacterial growth in industrial biotechnology, especially regarding the nitrogen content of the medium.