Cyanobacteria from benthic mats of Antarctic lakes as a source of new bioactivities

Aims: To exploit the cyanobacterial diversity of microbial mats growing in the
benthic environment of Antarctic lakes for the discovery of novel antibiotic
and antitumour activities.
Methods and results: In all, 51 Antarctic cyanobacteria isolated from benthic
mats were cultivated in the laboratory by optimizing temperature, irradiance
and mixing. Productivity was generally very low (£60 mg l)1 d)1) with growth
rates (l) in the range of 0Æ02–0Æ44 d)1. Growth rates were limited by photosensitivity,
sensitivity to air bubbling, polysaccharide production or cell aggregation.
Despite this, 126 extracts were prepared from 48 strains and screened for
antimicrobial and cytotoxic activities. Seventeen cyanobacteria showed antimicrobial
activity (against the Gram-positive Staphylococcus aureus, the filamentous
fungus Aspergillus fumigatus or the yeast Cryptococcus neoformans), and 25
were cytotoxic. The bioactivities were not in accordance with the phylogenetic
grouping, but rather strain-specific. One active strain was cultivated in a 10-l
photobioreactor.
Conclusions: Isolation and mass cultivation of Antarctic cyanobacteria and LCMS
(liquid chromatography ⁄ mass spectrometry) fractionation of extracts from
a subset of those strains (hits) that exhibited relatively potent antibacterial
and ⁄ or antifungal activities, evidenced a chemical novelty worthy of further
investigation.
Significance and impact of the study: Development of isolation, cultivation
and screening methods for Antarctic cyanobacteria has led to the discovery of
strains endowed with interesting antimicrobial and antitumour activities.