en عمومى General پژوهشي Research <strong>Background</strong>: Water plays an essential role in supporting life on earth and sea worldwide, requiringclean, safe, high quality and sustainable resources. Nowadays, many water resources have been contaminatedwith toxic compounds originating from petroleumdue to economical and industrial developments. There is anurgent need to clean up the waters with environmentally friendlyand inexpensive methods. This study investigated the biodegradation of total petroleum hydrocarbons (TPH) using <em>Pseudomonas aeruginosa</em> <em>(P.</em> <em>aeruginosa)</em> in southern Caspian Sea coastline.<br> <strong>Methods</strong>: Coastline sediment samples were collected, with <em>P. aeruginosa </em>being the predominant strain. The bacteria were cultured in triplicates in the presence of 0.5, 1, 2 and 4% of gasoline andunder specific experimental conditions of varying temperature, pH, salinity, shaker speed, and incubation periods. The data representing the gasoline biodegradation in the samples were statistically analyzed.<br> <strong>Results</strong>:&nbsp; At optimized experimental conditions for temperature, pH, salinity, incubation period, and shaker speed, maximum biodegradation of TPH was achieved by culturing <em>P. aeruginosa</em> strains with the sea water samples containing varying concentrations of gasoline<em>.</em><br> <strong>Conclusion</strong>: The gram-negative bacteria, <em>P. aeruginosa,</em> almost completely biodegraded TPH contaminants from the samples&rsquo; culture media over 28 days of incubation. We conclude that the use of <em>P. aeruginosa</em> is an efficient method for the biodegradation of Caspian coastal waters contaminated with TPH. Caspian Sea Waters, Gas Chromatography, Gasoline Biodegradation, Petroleum Hydrocarbons, Pseudomonas Aeruginosa 21 26 http://ijt.arakmu.ac.ir/browse.php?a_code=A-10-594-1&slc_lang=en&sid=1 Samira Mehrdad 100319475328460011473 100319475328460011473 No Department of Natural Resources and Environment, Science & Research Branch, Islamic Azad University. Tehran, Iran. Keivan Saeb keivansaeb@gmail.com 100319475328460011474 100319475328460011474 Yes Department of Environment, Tonekabon Branch, Islamic Azad University. Tonekabon, Iran. Lobat Taghavi 100319475328460011475 100319475328460011475 No Department of Natural Resources and Environment, Science & Research Branch, Islamic Azad University. Tehran, Iran. Masood Ghane 100319475328460011476 100319475328460011476 No Department of Microbiology, Tonekabon Branch, Islamic Azad University. Tonekabon, Iran.