Natural coumarins contribute to the aroma of licorice, and they are often used as a flavoring and stabilizing agents. However, coumarins usage in food has been banned by various countries due to its toxic effect. In this study, a strain of HSM-C2 that can biodegrade coumarin with high efficiency was isolated from soil and identified as Pseudomonas putida through performing 16S rDNA sequence analysis. The HSM-C2 catalyzed the biodegradation up to 99.83% of 1 mg/mL coumarin within 24 h under optimal culture conditions, such as 30 °C and pH 7, which highlights the strong coumarin biodegrading potential of this strain. The product, such as dihydrocoumarin, generated after the biodegradation of coumarin was identified by performing GC-MS analysis. The present study provides a theoretical basis and microbial resource for further research on coumarin biodegradation.

Sensory attributes strongly influence consumers’ preferences for products. The inoculation of the Klebsiella variicola H8 strain in a reconstituted tobacco leaf concentrate (RTLC) solution increased neutral aroma-enhancing compound (NAEC) production by 45%, decreased the nicotine level by 25%, decreased the water-soluble total sugar content by ~36%, and improved the sensory quality by 5.71%. The production of NAECs such as dihydrokiwi lactone (DHKL: 192.86%), 1,2,3,4-tetrahydro-1,1,6-trimethylnaphthalene (THTMN: 177.77%), 2,4-di-tert-butylphenol (DTBP: 25%), 4-oxoisofolkone (OIFK: 116.66%,) 1,9-heptadecadiene-4,6-diyn-3-ol (HDD: 116.67%), β-damastrone (BDS: 116.67), and megastigmatrienone A (MSTA: 116.67%) was increased. A metagenomics analysis of the microbial community in the fermented RTLC (FRTLC) was performed to elucidate the mechanism by which NAECs were produced. As a result, 24 groups of functional genes were identified, and among them, five families of carbohydrate-active enzymes, (i) glycoside hydrolase (GH), (ii) glycosyltransferase (GT), (iii) polysaccharide lyase (PL), (iv) carbohydrate esterase (CE), and (v) auxiliary active enzyme (AA), were found to be positively correlated with the production of NAECs. However, among the GHs, the GHs annotated from the H8 strain chromosome displayed the highest relative abundance and a positive correlation with the production of NAECs. Specifically, the GH13-14, GH13-20, GH13-38, GH13-25, GH13-10, GH42, and GH28 genes of the H8 strain were relatively more abundant and were key contributors to the production of NAECs. The correlation analyses revealed that the H8 strain plays a leading role among all the microorganisms in FRTLC in the production of NAECs. Our findings support the application of Klebsiella variicola in NAEC production and a reduction in nicotine content in tobacco products.

Z-abienol is a labdane diterpene present in tobacco leaves and is a key precursor for producing valuable aroma compounds such as ambrox. This study aimed to identify and characterize a bacterial strain that can efficiently degrade Z-abienol through microbial fermentation. The strain LSC-2 isolated from fresh tobacco leaves was identified as Acinetobacter tjernbergiae based on its morphological features and 16S rDNA phylogenetic analysis. Results of fermentation optimization experiments showed that the highest degradation efficiency of LSC-2 (69.3%) was achieved under the following conditions: 1 mg/mL Z-abienol, 0.5 mg/mL urea as the nitrogen source, pH 7, 30°C, and 150 rpm over 4 days. Whole-genome sequencing and functional annotation revealed that oxidoreductases, especially those from the auxiliary activity enzyme family, play a critical role in Z-abienol degradation. High-performance liquid chromatography and gas chromatography–mass spectrometry analysis confirmed the biotransformation of Z-abienol into various intermediates, including sclareol (211.3 μg/mL), scalaral (89.5 μg/mL), and amberonne (57.0 μg/mL). These intermediates have significant industrial applications, particularly in fragrance, pharmaceutical, and cosmetic industries. Sclareol serves as a key precursor in ambrox synthesis, a widely used fixative in high-end perfumery, whereas scalaral and amberonne enhance the aroma in tobacco and flavor formulations. The findings of this study provide valuable insights into the microbial degradation of Z-abienol, which will help develop a sustainable approach to producing bio-based fragrance compounds. Future studies should focus on enzymatic mechanisms and metabolic engineering strategies to improve the efficiency of biotransformation.

Cis-abienol is found in small quantities in plants like Nicotiana tabacum and Abies balsamea . It serves as a precursor for the synthesis of ambergris-like compounds, including ambroxide and ambreinolide, which are highly valued in the perfume industry for their long-lasting fixative properties and distinctive scent profile. This review summarises current progress in understanding (i) the biosynthetic pathways, chemical properties, and microbial or enzymatic degradation of cis-abienol in tobacco, particularly its production in glandular trichomes and its degradation during curing; and (ii) the chemical conversion of tobacco-derived cis-abienol and its analogues, such as sclareol, into ambrox, ambreinolide, and related fragrance compounds through oxidation, reduction, and cyclisation reactions. The bioconversion of cis-abienol or sclareol into ambergris-like compounds (AmbLCs) represents a sustainable and environmentally friendly alternative to traditional chemical methods; however, efficient biotechnological approaches for the direct biodegradation of cis-abienol into ambergris analogues remain underdeveloped. Future work should focus on metabolic engineering, enzyme discovery, and microbial pathway optimization to enhance the efficiency of these transformations, thereby laying the foundation for utilizing tobacco as a sustainable source of AmbLCs.

Alpha-cembratriene-4,6-diol (α-CBT-diol) is a complex diterpenoid primarily found in Solanaceae (i.e., tobacco leaves), Pinaceae, and marine corals. Due to its intricate chemical structure, it serves as a precursor for several aroma compounds, including farnesal. Farnesal and its derivatives have applications across various fields, such as the fragrance and flavor industry, pharmaceuticals, agriculture, and cosmetics. In this study, Stenotrophomonas maltophilia H3-1, a strain capable of efficiently biodegrading α-CBT-diol into farnesal, was isolated from soil and identified through 16S rDNA sequence analysis. S. maltophilia H3-1 biodegraded 93.3% of α-CBT-diol (300 mg/L) within 36 h when grown under optimized culture conditions, including a temperature of 40 °C, pH of 8, 2 g/L maltose, and 2 g/L ammonium sulfate. Theoretically, this strain can produce 201 mg/L of farnesal during the biotransformation of α-CBT-diol. The putative α-CBT-diol bioconversion pathway expressed in S. maltophilia H3-1 is also proposed. This is the first study to report the bioconversion of α-CBT-diol into the high-value compound farnesal using a novel S. maltophilia H3-1 strain. It highlights that other compounds found in tobacco can also be bioconverted into valuable products.