Identificação e caracterização fisiológica de bactérias termofílicas e termotolerantes isoladas do solo da caatinga do cariri paraibano

Abstract

Microorganisms from extreme environments, such as the caatinga, are adapted to the low water availably and high temperatures and can be a good source of enzymes with useful characteristics for biotechnological and industrial uses. Taking this into account, the objective of this work was to evaluate the diversity, production of extracellular enzymes and some of the physiological characteristics of bacteria isolated from caatinga soil from the São João do Cariri region, Paraíba. The identification and phylogenetic analysis of the isolates were based on molecular methods, such as genomic DNA extraction, amplification and sequencing of the 16S rDNA gene, and analysis of the sequences using bioinformatics tools. Bacterial growth was assessed in the 25°C - 70 oC temperature range. The analysis of the production of extracellular enzymes was conducted using the specific substrates carboxymethylcellulose, citrus pectin, starch, gelatin, residual vegetal oil and chitin for the detection of cellulase, pectinase, amylase, protease, lipase and chitinase enzymes, respectively. The bacterial isolates’ ability to use sugars (cellobiose, fructose, galactose, lactose, mannose, raffinose, xylose and salicin) and organic salts (sodium succinate and sodium citrate) as carbon sources were determined. It was found that the 28 tested isolates belonged to the Bacillus genus of the Firmicutes phylum, with 25 isolates showing similarity to the species B. subtilis and three to B. tequilensis. Regarding the growth temperature range, 25 of the isolates were classified as thermotolerant and three as thermophilic. All of the isolates produced at least two types of extracellular enzymes, with cellulases, proteases and lipases being the most common ones. Four isolates were capable of degrading five of the used substrates. The B. subtilis T28 isolate stood out on the production of amylase and protease and B. subtilis T45 of amylase and pectinase. Out of the 18 tested isolates, 12 had the ability to use at least two carbohydrates and 16 isolates were able to use both organic salts. The results of this study showed that some of the bacterial isolates from this understudied environment have the potential to be explored for the production of extracellular enzymes such as amylases, proteases and pectinases.