Atlantic Forest’s and Caatinga’s semiarid soils and their potential as a source for halothermotolerant actinomycetes and proteolytic enzymes

ABSTRACT

Actinomycetes are versatile about their metabolism, displaying high capacity to produce bioactive metabolites. Enzymes from actinomycetes represent new opportunities for industrial applications. However, proteases from actinomycetes are poorly described by literature. Thereby, to verify proteolytic potential of actinomycetes, the present study aimed the investigation of bacterial isolates from Caatinga and Atlantic Forest rhizosphere. Fluorescence resonance energy transfer (FRET) peptide libraries were adopted for the evaluations, since they are faster and more qualitative methods, if compared with others described by most reports. A total of 52 microorganisms were inoculated in different culture media (PMB, potato dextrose agar, brain heart infusion agar, Starch Casein Agar and Reasoner’s 2A agar), temperatures (12, 20, 30, 37, 45 and 60°C), and saline conditions (0–4 M NaCl), during 7 days. The actinomycetes named as AC 01, 02 and 52 were selected and showed enzymatic abilities under the peptide probes Abz-KLRSSKQ-EDDnp and Abz-KLYSSKQ-EDDnp, achieving enhanced performance at 30 °C. Biochemical parameters were established, showing a predominance of alkaline proteases with activity under saline conditions. Secreted proteases hydrolysed preferentially polar uncharged residues (Y and N) and positively charged groups (R). Phenylmethylsulfonyl fluoride and ethylenediaminetetraacetic acid inhibited the proteins, a characteristic of serine (AC 01 e 02) and metalloproteases (AC 52). All selected strains belonged to Streptomyces genera. In summary, actinomycete strains with halophilic proteolytic abilities were selected, which improve possibilities for their use in detergent formulations, food processing, waste management and industrial bioconversion. It is important to highlight that this is the first report using FRET libraries for proteolytic screening from Caatinga and Atlantic Forest actinobacteria.

GRAPHICAL ABSTRACT

KEYWORDS:

• FRET peptide
• metalloprotease
• rhizosphere
• serine
• proteolytic ability

Acknowledgements

The authors are thankful to UNIFESP and the Brazilian Agricultural Research Corporation (EMBRAPA Environment) for the technical support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Conceived and designed the experiments and wrote the paper: MAVS, SPV and JRC. Performed experiments: MAVS and SMBS. Analysed the data: MAVS, and DNO. Contributed reagents/materials/analysis tools: SPV, MAJ, JRC and ISM.

Data availability statement

The data that support the findings of this study are openly available in Repositório Unifesp at (https://repositorio.unifesp.br/handle/11600/59666?show=full), reference number 11600/59666. In addition, additional supporting data of this study are available from the corresponding author, SPV, upon reasonable request.

Additional information

Funding

This study was supported by grants from Coordination for the Improvement of Higher Education Personnel (CAPES – Scholarship 001) and São Paulo Research Foundation (FAPESP – 2010/51992-5 and 2016/23685-7).