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16 Mar 2016

Antibiotic Production and Resistance in the Microbial Community of Ulva Australis

Melani Sutrisno, January 2013
The University of New South Wales

Shigella flexnery and Shigella sonnei isolated from several countries have shown resistance to most antibiotics used for shigellosis treatment and therefore new antibiotics against the two bacteria are urgently needed. Although most antibiotics were discovered from soil microorganisms, the marine environment such as the microbial communities of the macro-algaUlva australis is potential sources for finding new antibiotics. Since most of the bacteria living in the alga are not readily cultured or “not-yet” cultured, metagenomics was applied to access the uncultured properties for antibacterial activity against the two species of Shigella. To optimally capture antibiotic synthesis genes, two host systems (Escherichia coli andStreptomyces lividans) were used. Moreover, to obtain a link information of such functions into the phylogenetic origin of the organisms, Homing Endonuclease Restriction and Marker Insertion (HERMI) was applied. The functional screening of the metagenomic library expressed in the two host cells resulted in the identification of an antibiotic synthesis gene, possibly encoding for a microcin-like antibiotic. HERMI, a valuable technique in phylogenetic analysis of metagenomic library, has produced a HERMI clone for phylogenetic analysis and identification of gene properties. The HERMI clone was identified as a new, uncultured bacterium with only 79% identity to the 16S rRNA of Hyphomonas oceanitis.  Five antibiotic resistant clones were obtained from the HERMI application and five genes encoding for beta-lactamases were characterized. It was revealed that both clinical and novel beta-lactamases were present in the microbial communities. The gene encoding for putative cell wall-associated hydrolase which are distantly similar to the existing sequences were identified. Furthermore, genes for virulence (Toll/ interleukin-1 receptor protein and leucine-rich repeat protein-like protein) were identified, indicating the presence of pathogens in the alga. Overall, the microbial communities of U. australis have possible important properties for pharmaceutical applications and further experiments will be needed to uncover the compounds.

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