Biofilms of Halobacterium salinarum as a tool for phenanthrene bioremediation.

The use of hyperhalophilic microorganisms is emerging as a sustainable alternative to clean hydrocarbon-polluted hypersaline water bodies. In line with this practice, this work reports on the ability of the archaeon Halobacterium salinarum to develop biofilms on a solid surface conditioned by the presence of phenanthrene crystals, which results in the removal of the contaminating compound. The cell surface hydrophobicity does not change during the removal process and this organism is shown to constitutively produce a surfactant molecule with specific action on aromatic hydrocarbons, both indicating that phenanthrene removal might proceed through a non-contact mechanism. A new approach is presented to follow the process in situ through epifluorescence microscopy by monitoring phenanthrene auto-fluorescence.

Seasonal dynamics of extremely halophilic microbial communities in three Argentinian salterns.

Seasonal sampling was carried out at three Argentinian salterns, Salitral Negro (SN), Colorada Grande (CG) and Guatraché (G), to analyze abiotic parameters and microbial diversity and dynamics. Microbial assemblages were correlated to environmental factors by statistical analyses. Principal component analysis of the environmental data grouped SN and CG samples separately from G samples owing to G's higher pH values and sulfate concentration. Differences in microbial assemblages were also found. Many archaeal sequences belonged to uncultured members of Haloquadratum and Haloquadratum-related genera, with different environmental optima. Notably, nearly half of the archaeal sequences were affiliated to the recently described 'Candidatus Haloredividus' (phylum Nanohaloarchaeota), not previously detected in salt-saturated environments. Most bacterial sequences belonged to Salinibacter representatives, while sequences affiliated to the recently described genus Spiribacter were also found. Seasonal analysis showed at least 40% of the microbiota from the three salterns was prevalent through the year, indicating they are well adapted to environmental fluctuations. On the other hand, a minority of archaeal and bacterial sequences were found to be seasonally distributed. Five viral morphotypes and also eukaryal predators were detected, suggesting different mechanisms for controlling prokaryotic numbers. Notably, Guatraché was the saltern that harbored the highest virus-to-cell ratios reported to date for hypersaline environments.

Exploring the multiple biotechnological potential of halophilic microorganisms isolated from two Argentinean salterns.

The biodiversity and biotechnological potential of microbes from central Argentinean halophilic environments have been poorly explored. Salitral Negro and Colorada Grande salterns are neutral hypersaline basins exploded for NaCl extraction. As part of an ecological analysis of these environments, two bacterial and seven archaeal representatives were isolated, identified and examined for their biotechnological potential. The presence of hydrolases (proteases, amylases, lipases, cellulases and nucleases) and bioactive molecules (surfactants and antimicrobial compounds) was screened. While all the isolates exhibited at least one of the tested activities or biocompounds, the species belonging to Haloarcula genus were the most active, also producing antimicrobial compounds against their counterparts. In general, the biosurfactants were more effective against olive oil and aromatic compounds than detergents (SDS or Triton X-100). Our results demonstrate the broad spectrum of activities with biotechnological potential exhibited by the microorganisms inhabiting the Argentinean salterns and reinforce the importance of screening pristine extreme environments to discover interesting/novel bioactive molecules.

Hyperhalophilic archaeal biofilms: growth kinetics, structure, and antagonistic interaction in continuous culture.

Biofilms by the hyperhalophilic archaea Halorubrum sp. and Halobacterium sp. were analyzed, and for the first time the progression of structural features and the developmental parameters of these sessile populations are described. Optical slicing and digital analysis of sequential micrographs showed that their three dimensional structure was microorganism dependent. Biofilms of Halobacterium sp. developed in clusters that covered about 30% of the supporting surface at the interface level and expanded over about 86 ± 4 µm in thickness, while Halorubrum sp. biofilms covered less than 20% of the surface and reached a thickness of 41 ± 1 µm. The kinetics of growth was lower in biofilms, with generation times of 27 ± 1 and 36 ± 2 h for Halobacterium sp. and Halorubrum sp., respectively, as compared to 8.4 ± 0.3 and 14 ± 1 h in planktonic cultures. Differences between microorganisms were also observed at the cell morphology level. The interaction between the two microorganisms was also evaluated, showing that Halobacterium sp. can outcompete already established Halorubrum sp. biofilms by a mechanism that might include the combined action of tunnelling swimmers and antimicrobial compounds.