Unveiling the bioactive potential of marine bacteria

• Autor(a) principal: João, Susana Afonso
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/32822
• topic: Bioactive compounds; Antimicrobial activity; Antibiotics; OSMAC; PKS-I; NRPS; Triparental mating

Besides a primary metabolism, living organisms possess a secondary metabolism which allows for the production of secondary metabolites that, normally, are not fundamental to the organism’s growth and survival. These metabolites allow for a better adaptability to their environment as they act as defence mechanisms, can be bioactive against several pathogenic agents and can be used as drugs to efficiently eliminate them. At first, the search for new natural compounds by the scientific community was based on terrestrial environments. However, more recently, more and more attention has been paid to the oceans. Since there has been a general abuse in the use of antibiotics, the numbers of antibiotic resistant bacteria have been rising rapidly. Therefore, it is essential to invest in the discovery new compounds that can be used as alternatives to the traditional antibiotics. The main aim of this work was the analysis of the antimicrobial potential of a collection of marine bacteria by molecular and screening assays. Aiming at obtaining a higher yield of secondary metabolites, in this work a transformation of the planctomycete Roseimaritima ulvae UC8T was performed using the triparental mating technique. This bacterium was chosen since Planctomycetes have shown promising bioactive potential. However, this strain exhibited the production of some kind of bioactive compounds that inhibited the growth of Escherichia coli ATCC 25922 and possibly affected the growth of the donor and helper E. coli DH5α involved in the transformation process. In parallel, a molecular screening for the amplification of polyketide synthases type I (PKS-I) and non-ribosomal peptide synthetases (NRPS) was performed in 329 newly isolated strains which belong to Laboratório de Ecofisiologia Microbiana da Universidade do Porto (LEMUP) collection. From these strains 36% generated amplicons for PKS-I and 24% for NRPS. The rest did not amplify for either one of these genes. Then, a selection was made based on the amplification for these genes and the promising strains were chosen to be tested against E. coli ATCC 25922 and Staphylococcus aureus ATCC 29213. Furthermore, a one strain many compounds (OSMAC) approach was performed to the strains that showed to be bioactive in the preliminary antimicrobial assay in 5 different culture media (1:10 M607, M607, M600, MA and CGY). From all the bacteria that were selected only 16 strains were considered bioactive, and mostly against E. coli ATCC 25922, unlike Streptomyces flavoviridis PMIC_1A8B which was highly bioactive against S. aureus ATCC 29213. Most of the bioactive strains belong to the Actinobacteria phylum except for Arenibacter aquaticus PMIC_1E11B.2, Aquimarina algiphila PMO90_19.1 and the new species PMO138_17 closely affiliated with Methylotenera mobilis. In the OSMAC assay, the highest values of bioactivity were obtained in extracts from strains grown in 1:10 M607, the lowest nutrient rich culture medium. Also, high activities were displayed in the more nutrient rich CGY culture medium. In conclusion, the OSMAC approach showed the importance of the culture medium composition for the production of bioactive molecules.