Session: Recent Advancements in Lignin Valorization Strategies for Fuels and Chemicals:

The veterinary antibiotic chlortetracycline can enter the environment through various ways, such as land-applied manure and effluents from concentrated animal feeding operations (CAFOS). Lands contaminated with antibiotics can be efficiently treated by plants (phytoremediation), and the plant biomass, unsuitable to food production, can subsequently be used for the production of biofuel. However, prior research has shown that plant exposure to toxic species (e.g., toxic metals) accumulate higher levels of lignin, which can then impair the biomass digestion and its conversion into bioethanol. The objective of this study was to examine the impact of chlortetracycline on lignin biosynthesis to the model plant, Arabidopsis thaliana. Toxicity testing indicated that exposure to chlortetracycline exhibited a dose-dependent toxicity, with an effect concentration 50% (EC50) = 8.1 ± 2.3 and 4.6 ± 0.2 mg L^-1, based on the growth and germination tests, respectively. The effect of chlortetracycline on Arabidopsis was then investigated at the molecular level. Whole genome expression analysis was conducted using RNA sequencing, which allowed to identify 564 genes differentially expressed by exposure to chlortetracycline (adjusted p-value < 0.05), including 480 (85.1%) upregulated genes (fold change > 2.0) and 84 (14.9%) down regulated genes (fold change < 0.5). Exposure to chlortetracycline resulted in significant enrichment of genes involved in lignin biosynthesis, including beta-glucosidases, glycosyl hydrolases, cinnamyl alcohol dehydrogenases, and peroxidases, which suggest induction of lignin biosynthesis. Other genes overexpressed by chlortetracycline are involved in response to different types of stresses and the metabolism of xenobiotic compounds, including glutathione S-transferase and cytochrome P-450, which is consistent with the observed phytotoxic effects of chlortetracycline. The actual accumulation of lignin in exposed plants was then investigated using Fourier-transformed infrared spectroscopy (FTIR). Four spectral second-derivative absorbance peaks correlated with lignin were identified in the fingerprint region, indicating that exposure to chlortetracycline caused a 15.6 to 40.1% increase of the lignin content. Our results may have important implications for the conversion of biomass from phytoremediation applications to biofuel.

Aaron Newborn

George Mason University

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