Bacteria with tolerance against lithium-chloride and their differential growth through SEM observation

MARTÍNEZ FABIANA; RAJAL VERÓNICA; IRAZUSTA VERÓNICA

Córdoba

Congreso; XI SAMIGE Congreso Argentino de Microbiología general; 2015

Fossil fuels, being non-renewable resources will eventuallycome to an end. This is the main reason why alternative energies are beingstudied. Clean energies are the most important and are thought as the futuresources of energy for the planet.Lithium batteries have a special importance in this area because of their efficiency, since theycan save relatively large amounts of energy in small sized and lightweightbatteries.Trapping lithium compounds from the environmentthroughmicrobial mechanisms would be really interesting because of the great uses itcould have (soil decontamination after incorrect batteries disposal andobtaining lithium for battery production). Our investigation focuses onsearching for microorganisms that are able to interact with lithium and grow inhigh-lithium concentration environments.After isolating bacteria from water and soil samplesfrom El Salar del Hombre Muerto (Argentina), one of the most lithium-richbrines from South America, we selected the most tolerant to lithium chloride.Starting with 54 bacterial isolates, the following experiment was carried out:the bacteria were inoculated in 5 ml of minimum media (MM) with different lithiumchloride concentrations and the tubes were incubated at 30°C and 200 r.p.m for 5days. Growth was evaluated qualitativelyby the development of turbidity,filamentous or pellets. Twenty-nine out ofthe 54 initial isolates grew until 30g/l LiCl, and only6 of themat 60 g/l LiCl. In order to determine the cell structure in presenceof lithium, we selected 7 strains to be observed by SEM: four that grew upuntil 30 g/l LiCl and three that grew at 60 g/l LiCl were analyzed. For that, theisolates were grown in 50 ml of MM without salt and with 30 g/l LiCl in 250 mlErlenmeyer flasks. After a week of incubation, the cells were harvested bycentrifugation at 5400 rpm, fixed with formaldehyde and dehydrated by serialwashes with increasing alcohol concentrations, until absolute alcohol.Then, thedehydrated samples were taken to LASEM (Laboratory of Scanning ElectronMicroscopy and Microanalysis) for the proper treatmentfor SEM observation (criticalpoint drying and gold-covering).The cells grown in MM without LiCl showed adefined and normal shape. Interestingly, when grown in presence of LiCl, somecells were more round-shaped and in most cases an exopolysaccharide-like substancecould be seen covering them. It is well documented in the literature that oneof the mechanisms used by microorganisms against adverse conditions is the productionof this kind of substances and the formation of biofilms, so it can be the caseof our bacteria. We are looking forward in the future to establish thespecific function and composition the secreted substance and the significanceof changes in cell shape. Further investigation will be conducted to study thedifferential gene expression of the microorganisms for protein production in thepresence and absence of lithium chloride.