Abstract

Microorganisms contained in estuary water samples (Deltebre, Spain) have been the subject of several tests of resistance against various chemicals, such as heavy metals, hydrocarbons, and antibiotics. Isolates were plated (cultivated) on Trypticase Soy Agar plates and purified for further screening. The strains were extremely resistant to heavy metals, with peculiarly, high average minimal inhibitory concentration (18700 µmol/l for arsenic and 10600 µmol/l for lead), and they also showed that they were able to grow in the presence of significant concentrations of sodium chloride (more than 50 g/l), and an interesting resistance to hydrocarbons, and antibiotics. Results showed that the most resistant strains to all the tested pollutants belong to Pseudomonas putida and Stenotrophomonas maltophilia. The kinetics of growth in the presence of certain heavy metals (Arsenic (9600 µmol/l), Cobalt (1200 µmol/l), and Lead (4600 µmol/l)), showed that the isolates had a great ability to multiply in presence of such growth inhibitors, even in high concentrations. The study of growth of the isolated strains in the presence of aromatic hydrocarbons (Benzene (4 mmol/l), Toluene (4 mmol/l), Naphthalene (6 mmol/l)) as the sole carbon source was also carried out.  Isolates showed a significant sensitivity in the presence of high concentrations of hydrocarbons however, the proliferation was surprisingly fast in the presence of naphthalene. The isolated strains have shown that they can be of considerable significance, regarding the remediation of some heavy metals and aromatic compounds in heavily polluted sites.

Key words: Heavy metals resistant bacteria, antibiotics resistance, hydrocarbons resistance, salt tolerance, bioremediation, seawater.