Sterilize Methods Comparison for Soils: Cost, Time, and Efficiency

Soil sterilization is generally used to eliminate or reduce microbial activity in studies involving microbial inoculations, soil enzymes, among others. Achieving an adequate sterility condition is not straightforward due to the variety of resistance structures that are generated in soil microbial ecosystems and the reservoirs that can form between soil aggregates. This is why finding an effective method to achieve good sterilization is important in methodological terms, so the present work aims to compare the effectiveness of three widely used methodologies to sterilize soil and to evaluate their cost/benefit in terms of time and inputs invested. Four treatments were tested: gamma irradiation, sterilization cycles at different times: three cycles of 1 h each and four cycles of 15 min each, and chloroform vapors. The evaluation and comparison of all samples sterilized by the different methodologies were based on the total aerobic heterotrophic bacterial count. The results of this study suggest that it is more efficient to use autoclaving methods because the process is more accessible in terms of equipment and methodologies, and the final results are the same. In the case of this work, sterilization with chloroform vapors had to be rejected. While the use of gamma radiation may be more efficient in terms of time, it can be a costly and inaccessible service for some laboratories that do not have the equipment. Therefore, the most viable options in terms of time, cost, and benefit are those using autoclaves. Among these, shorter treatment times mean a reduction in the cost of using the equipment, so the option of 15-minute cycles is desirable.