Effect of temperature change on bacterial degradation of selected pharmaceutical and personal care products (PPCPs)
This study investigated the fate, transport, and remediation of potentially harmful contaminants and their by-products at different environmental temperatures. Spiked soil was incubated at different temperatures and analyzed for micro-pollutant concentration after 90-days incubation. This was to determine the degradation rate, reaction of soil microbial community to the stress associated with some pharmaceutical and personal care products (PPCPs) in the soil, and the effect on the bacterial community composition 24-hours after exposure and post incubation. In Chapter 2, I examined the effect of temperature in the presence of estrone (E1), triclosan (TCS), ciprofloxacin (CPFX), ibuprofen (IBU), naproxen (NPX), caffeine (CAF), and diclofenac (DIC) singly and as a mixture on soil microbial community metabolic diversity and how temperature influences degradation rates singly or in mixture. I found that most PPCP degraded faster at 20°C and 30°C and that half-lives were lower in the single compound incubation than mixtures. The community-level physiological profiling (CLPP) over time revealed that at 10°C revealed that temperature affected the metabolic profiles of most PPCPs including control treatments. At 20°C and 30°C, control treatment was not affected by temperature however, some treatments were affected initially but were able to revert to a pre-disturbance physiological state after 90 days however, some treatments could not revert to the initial state of utilization of carbon source as seen on day 0. In Chapter 3, I used 16S amplicon sequencing to investigate how microbial community composition and diversity was affected in the presence of ciprofloxacin and naproxen in comparison to a control treatment that had no PPCP added to it at two temperatures (10°C and 30°C). Also, I used the 16S amplicon data generated to predict microbial community function. My results showed that microbial communities at the lower temperature were most affected in terms of diversity and composition. Functional analysis showed that treatments of CPFX and NPX at 10°C had the least number of functional genes detected. Functional analysis using FAPROTAX revealed there was either a decrease or loss in the CPFX or NPX samples of functions related to compound transformation, and carbon and nitrogen cycling. In chapter 4, I examined the effect of temperature in the presence of estrone, triclosan, naproxen, diclofenac, ciprofloxacin, ibuprofen, and caffeine mixture on soil bacterial community when incubated at two environmentally relevant temperatures (10°C & 30°C) in a laboratory setting and explored the changes in the bacterial community over time using 16S rRNA gene sequencing. My result indicated that temperature affected bacteria community richness and evenness. Beta diversity analysis revealed that soil samples exposed to the PPCP treatment were different from control samples at the two incubated temperatures. Functional analysis using FAPROTAX revealed that treatments spiked with the suite of PPCPs at 30°C showed an increase in functional genes for nitrogen fixation and manganese oxidation. Overall, I found out that different temperatures could positively or negatively impact the microbial community involved in the degradation of PPCPs in the soil by either increasing or reducing their abundance, alter their composition, or change the functional diversity of the community. Despite this, the microbial community is capable of breaking down these compounds in the soil. Understanding environmental factors such as temperature, that aid in faster degradation of PPCPs and is altered by climate change, will go a long way to elucidate ways to reduce PPCP contamination in the soil environment and incorporating it into the process of wastewater treatment thus prevents them from getting into ground water or being taken up by food crops when wastewater is used for irrigation purpose.
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