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

FABIANA MARTÍNEZ; VERÓNICA B. RAJAL; VERÓNICA IRAZUSTA

Córdoba

Congreso; XI Congreso Argentino de Microbiología General ?SAMIGE; 2015

Fossil fuels, being non-renewable resources will eventually come to an end. This is the main reasonwhy alternative energies are being studied. Clean energies are the most important and are thought asthe future sources of energy for the planet. Lithium batteries have a special importance in this areabecause of their efficiency, since they can save relatively large amounts of energy in small sized andlightweight batteries. Trapping lithium compounds from the environment through microbialmechanisms would be really interesting because of the great uses it could have (soil decontaminationafter incorrect batteries disposal and obtaining lithium for battery production). Our investigationfocuses on searching for microorganisms that are able to interact with lithium and grow in high-lithiumconcentration environments. After isolating bacteria from water and soil samples from El Salar delHombre Muerto (Argentina), one of the most lithium-rich brines from South America, we selected themost tolerant to lithium chloride. Starting with 54 bacterial isolates, the following experiment wascarried out: the bacteria were inoculated in 5 ml of minimum media (MM) with different lithium chlorideconcentrations and the tubes were incubated at 30°C and 200 rpm for 5 days. Growth was evaluatedqualitatively by the development of turbidity, filamentous or pellets. Twenty-nine out of the 54 initialisolates grew at 30 g/l LiCl, and only 6 of them at 60 g/l LiCl. Seven strains were selected, 6 of whichare rod shaped and only one is coccus. Gram staining allowed us to determine that 5 of them werefound to be Gram negative bacteria and 2, Gram positive. Taxonomic identification is underway.These isolates were also observed by SEM. For that, they were grown in 50 ml of MM without salt andwith 30 g/l LiCl in 250 ml Erlenmeyer flasks. After a week of incubation, the cells were harvested bycentrifugation at 5400 rpm, fixed with formaldehyde and dehydrated by serial washes with increasingalcohol concentrations, until absolute alcohol. Then, the dehydrated samples were taken to LASEM(Laboratory of Scanning Electron Microscopy and Microanalysis) for the proper treatment for SEMobservation (critical point drying and gold-covering). The cells grown in MM without LiCl showed adefined and normal shape. Interestingly, when grown in presence of LiCl, some cells were moreround-shaped and in most cases an exopolysaccharide-like substance could be seen covering them. Itis well documented in the literature that one of the mechanisms used by microorganisms againstadverse conditions is the production of this kind of substances and the formation of biofilms, so it canbe the case of our bacteria. We are looking forward in the future to establish the specific function andcomposition the secreted substance and the significance of changes in cell shape. Furtherinvestigation will be conducted to study the differential gene expression of the microorganisms forprotein production in the presence and absence of lithium chloride.