Microalgas: Cultivo em subproduto do café, caracterização do metaboloma, avaliação do efeito antimicrobiano e aplicação na síntese de nanopartículas

Abstract

Microalgae have been recognized as promising microorganisms due to their potential to generate value-added products. Because of their composition rich in carbohydrates, lipids, proteins and other bioactive compounds, microalgae are suitable for a variety of industrial applications. The present work aimed to isolate microalgae from two different Brazilian areas, and to evaluate their cultivation in coffee processing by-products. Additionally, the potential of Desmodesmus sp. and Neodesmus sp. to perform biosynthesis of silver nanoparticles, and also their antimicrobial properties were investigated. Microalgae were isolated from a lake located in Ijaci, in the state of Minas Gerais, and two bays in Portel and Melgaço, in the state of Pará. The isolation was performed according to the spread-plating method using BG-11, Bold and Bold medium supplemented with soil extract for seven days at 27ºC and 12h photoperiod. Seven isolates were obtained and morphologically characterized. After screening in mixotrophy of the media BG11 supplemented with 1g/L of glucose and indoor conditions and coffee wastewater (CWW) at 30, 60, and 90% concentrations, microalgae AL_UFLA06, which presented the highest growth, was selected to be cultivated in coffee silverskin (CSS) hydrolysates produced from different thermic reactions with CSS and water. The growth of AL_UFLA06 both in CWW and CSS was compared, and the concentration of 30% of CWW provided the highest growth, hence, AL_UFLA06 was selected for the next step of the experiment. The isolate was identified by sequencing its ITS region as Neodesmus sp. Mixotrophic growth in the selected condition was scaled-up and carried out indoors and outdoors (greenhouse) for eight days, with BG-11 as an autotrophic control. Cultivation using CWW in the outdoor environment presented the best biomass productivity, resulting in 1.64 g/L in eight days, compared to the production of 0.97 g/L under autotrophic growth and the same type of environmental condition. Carbohydrates (0.53 g/L), pigments (15.8 mg/L), lipids (1.1%), and proteins (0.2 g/L) content in CWW were higher than autotrophy also in outdoor growth. Intracellular metabolites identified by GC-MS reinforced the differences in microalgae composition between CWW and autotrophic growth outdoors. Higher accumulation of sugars and organic acids related to energy metabolism was observed in mixotrophy with CWW. In order to evaluate the potential for biotechnological applications, extracellular compounds released by Desmodesmus sp. and Neodesmus sp., in the cell-free culture supernatant after 14 days growth (27ºC, 12h photoperiod in BG-11) were collected by centrifugation, used as reducing agents of silver nitrate in concentrations of 0.5, 0.75, and 1mM, and then the biosynthesis of silver nanoparticles was performed. For antimicrobial activity screening, ethanolic and ethyl acetate extracts of Desmodesmus sp. and Neodesmus sp. were tested against pathogenic bacteria. Intracellular compounds present in the ethanolic and ethyl acetate extracts of Desmodesmus sp. showed antimicrobial activity against bacteria Staphylococcus aureus and Salmonella Typhimurium. Results highlight the potential of CWW for Neodesmus sp. growth, the microalgae adaptation to the cultivation outdoors, and also the potential of these microalgae for the development of antimicrobial agents and silver nanoparticles.