Potencial biotecnológico de bactérias e leveduras isoladas da casca do Coco-verde (Cocos Nucifera) em fermentação

Abstract

The culture of coconut is economically relevant to Brazil but suffers with the breeding of pests that target coconut trees and bring on economic losses. One of the pests responsible for such is the palm weevil R. palmarum L., which is attracted to the infestation site by the odor released from the fermentation of plant tissues. This is particularly problematic when the crop, processing and disposal sites are in close location, for the residue discarded (i.e. green coconut shell) undergoes the action of microorganisms that produce volatile compounds and attract the pest to the crop site. This research had as its objective the isolation and characterization of bacteria and yeasts responsible for the fermentation of green coconut shell and production of volatile compounds that are attractive to the palm weevil. For such, green coconut shells were exposed to the local environment for the development of the fermentative processes, having the emitted volatiles analyzed on five different days of fermentation (0, 3, 5, 7, and 10 days). Thirty different compounds belonging to different chemical classes were detected for all of the analyzed days, being alcohols, ketones, aldehydes and hydrocarbons the most frequently found. Isolation procedures were performed immediately after the opening of the coconuts and at the sixth day of fermentation. After purification, thirty eight strains (15 bacteria and 23 yeasts) were obtained and characterized. The characterization of the strains was based on the determination of orphological, physiological and biochemical characteristics and the evaluation of the biotechnological potential. The isolated strains presented variable biochemical profile, although each of them displayed at least one positive result for the tested enzymes. Although bacterial isolates were halotolerant, yeast strains were more. Among the bacterial strains, the isolate A5 stood out for displaying activity for all of the tested enzymes except for laccase besides being capable of degrading filter paper in liquid media. The isolate E4 stood out among the yeast strains for presenting activity for five of the tested enzymes (amylases, pectinases, xylanases, proteases and lipases/esterases) besides displaying tolerance up to 10% NaCl. Therefore each strain presented different biotechnological potential, some of them being potential candidates for the production of volatile compounds by fermentation of the green coconut shell. A few strains were identified to the genus level by the technique of MILDI-TOF, resulting in identification of three bacterial (Bacillus, Pantoea e Arthrobacter) e three yeasts (Pichia, Cryptococcus e Rhodotorula) genera. The production of volatile compound by four selected strains was investigated and resulted on the detection of over 100 different compounds, among which are included ketones, carboxylic acids, pyrazines, esters, hydrocarbons, aldehydes, terpenes and terpenoids. A few of the detected volatiles had been previously reported as attractive to R. palmarum confirming that there is a relationship between the metabolic activity of the isolated microorganisms and production of volatiles attractive to this pest.