Influence of Abiotic Factors Temperature and Water Content on Bacterial 2-Chlorophenol Biodegradation in Soils

Abstract

Halogenated compounds are environmental pollutants toxic to humans and wildlife. Certain microorganisms degrade these halogenated compounds. However, little is known about the potential of microorganisms in bioremediation under extreme conditions, specifically in arid and semi-arid soils frequently exposed to high temperatures and desiccation periods. Arid and semi-arid environments and deserts make up vast areas of Earth's landmass. To investigate the degradation of 2-chlorophenol (2-CP) in soils as a function of temperature and water availability, three bacterial species were tested, two soil mesophiles of the genus Rhodococcus, R. opacus and R. erythropolis, and a soil thermophilic isolate, Parageobacillus thermoglucosidasius. Degradation trials in soil samples with these species were performed over a range of water activity from 1 to 0.4. At their optimum growth temperature, R. opacus showed maximum 2-CP degradation at water activity 0.9 sharply decreasing when lowering water activity. Nevertheless, the Parageobacillus isolate (optimum growth temperature 60 • C) showed maximum 2-CP degradation rates at water activity 0.5 which represented highly desiccating conditions. Parageobacillus degradation of 2-CP was very low at water activity above 0.9. Thus, biodegradation of 2-CP in soils is possible even under arid conditions although different microbial species might be involved in this task depending on the interactions of abiotic factors and the diversity of microbial communities in soils. These results contribute to understand the potential biodegradation of specific halogenated compounds in the environment which is of great relevance to comprehend the fate of halogenated pollutants (i.e., 2-CP) in deserts, arid and semi-arid soils.

Environmental factors affect the response of microbial extracellular enzyme activity in soils when determined as a function of water availability and temperature

“…Climate changes will ultimately result in variations in microbial community diversity (Delgado-Baquerizo et al, 2016) and in its capability to decompose organic matter through the use of microbial extracellular enzymes (Gonzalez et al, 2015;Hammerl et al, 2019;Li et al, 2018;Moxley et al, 2019;Wallenstein & Weintraub, 2008).…”

“…Unlike previous studies, we carry out EEA estimates in soils accounting for soil properties such as water activity and temperature. Recently, Moxley et al (2019) reported a first approach to estimate microbial activity under low water availability conditions and without the addition of large amounts of salts or water activity-reducing compounds. This novel methodology allows to determine the actual effect of soil water content on microbial EEA.…”

“…Steinweg et al (2012) carried out EEA assays at temperatures in the range from 15 to 35°C approaching different moisture levels (mostly covering high water activity conditions) to estimate temperature and water activity sensitivity. At present, there is highly limited information on how water availability rules the activity of microorganisms and their enzymes in soils (Biederman et al, 2016;Moxley et al, 2019). Temperatures for the incubation of the enzyme assays were selected to represent soil conditions and common natural ranges for the extracellular enzyme activity from mesophilic (Fierer, Colman, Schimel, & Jackson, 2006;Townsend, Vitousek, & Holland, 1992) and thermophilic (Gonzalez et al, 2015) microorganisms and looking for facilitating the discrimination between mesophiles and thermophiles in the EEA assays.…”

“…Extracellular enzyme activity assays were carried out in soil samples over different water activities (see below), decreasing values from 1 down to the water activity resulting in zero or near-zero enzyme activity (Moxley et al, 2019).…”

Editorial: Environment and Health

“…Di Bella et al (2020) presented original results about a suite of organic and inorganic contaminants detected in food (terrestrial and seafood) from highly contaminated sites in southern Italy offering original approaches to assessment of associated health risk for different age profiles. Moxley et al (2020) presented detailed results on the biodegradation efficiency of halogenated compounds in contaminated soils using groups of meso-to thermophilic microorganisms under the extreme conditions of arid and semi-arid areas. Francocci et al (2020) presented a comprehensive view and original applications of the circular bioeconomy applied to contaminated sites as valuable holistic solution for restoration/recovery of large polluted sites.…”