Present work deals with the bio-mitigation potential of gaseous phase CO2 by chemolithotrophic bacterium Halomonas stevensii isolated from haloalkaliphilic habitat using thiosulfate ion (S2O32-) as an energy source. H. stevensii was tested for various abiotic stress tolerances such as salt [2-12% (w/v)], temperature (10-60 degrees C) and pH (2-12). Batch studies were conducted for 6 days at 15 (11) % (v/v) inlet CO2 concentration to find the CO2 fixing capability of H. stevensii under varying concentration of energy substrate i.e. 0, 50 and 100mM Na2S2O3. Approximately 98% CO2 removal from gaseous phase was achieved at 50 and 100 mM Na2S2O3. Evaluation of CO2 fixation by H. stevensii and carbon allocation into different cellular organic pool (carbohydrate, proteins and primary metabolite) was carried out by growing H. stevensii at 5%, 10% and 15% (v/v) inlet CO2 concentration for the duration of 6 days. The obtained leachate was quantified using chemical technique, FF-IR and GC. Utilization of gaseous phase CO2 by H. stevensii was also proven by conducting the approximate materials balance and energy assessment for the present CO2 fixation process. The mechanism of CO2 metabolism by H. stevensii was evaluated using GC-MS and carbon partitioning into cellular organic pool analysis. (C) 2017 Elsevier Ltd. All rights reserved.