Tobacco: A Favorite for Low-Carbon Biorefinery

Abstract

Biomass is increasingly recognized as a renewable source for the replacement of fossil fuel, as well as for the production of fuel and chemical production, due to its organic nature, abundant supply, and potential for negative emission. However, a cost-efficient bioconversion process, along with promising alternatives and streamlined utilization routes to chemicals, remains essential for the commercial deployment of biomass. Tobacco, a controversially planted crop primarily used as raw materials in the cigarette industry, has gained attention in light of the global adoption of the WHO Framework Convention on Tobacco Control (WHO FCTC) and the rising interest in its seed oil. Its high-yielding, broad cultivation, and suitability for genetic engineering have led to its consideration as a candidate for biofuels production. Nevertheless, neither the tobacco plant for production of seed oil or the hydrothermal process applied to tobacco biomass has established it as a viable feedstock candidate. A recent study published in The Innovation by Wang et al. [1] has proposed a novel and simplest strategy that promotes tobacco as a highly promising energy crop for bioproducts production, with the potential to significantly reduce greenhouse gas emissions (Figure 1).

Unlike traditional biomass feedstocks, tobacco was characterized by its high content of water-soluble carbohydrates (65%) (Figure 1a) and nitrogen, along with a low level of lignocellulose, and it is capable of growing on marginal lands, rendering it an ideal material for low-energy and low-carbon bioconversion processes. By simply autoclaving tobacco leaves in water, a nutrient medium was obtained that effectively supported the growth of microorganisms and the production of bioproducts (Figure 1c), eliminating the need for pretreatment and hydrolysis of the feedstock or the addition of supplements to medium. Additionally, the study employed a life cycle assessment (LCA) approach to evaluate the carbon-negative effects of tobacco biomass in the bioethanol production process. The findings indicated that tobacco bioethanol could reduce carbon emissions by up to approximately 76% and lower energy consumption by approximately 81% compared to traditional corn stover bioethanol during biorefinery processes (Figure 1b).

Massive biomass production and growth on marginal lands are two scientifically significant criteria for identifying a paradigmatic energy crop. Tobacco (Nicotiana tabacum) is among the most widely cultivated non-food crops globally, grown in over 100 countries. Tobacco cultivation can yield multiple harvests per year and produces a substantial biomass (Figure 1d), potentially reaching up to 170 tons/ha when cultivated for biofuel and biochemical production [2]. Its whole genome was published in 2014 [3], and numerous advanced genetic engineering tools are now available for its manipulation. Consequently, tobacco is amenable to genetic engineering, enabling its leaves to store increased hydrocarbon molecules and exhibit tolerance to saline-alkali stress tolerance as well as adaptability to extreme condition [4, 5]. Notably, tobacco has been successfully planted on saline-alkaline land at a large scale in Dongying, China. Thus, tobacco emerges as a non-food crop capable of growing on marginal or barren areas, and its ease of genetic engineering positions it as a key solution to avoiding competition with food production while ensuring high yield and cost-effective biomass production. Moreover, tobacco is a leafy plant, and its maturity and drying method significantly influence the accumulation of water-soluble components and sugars, which supports the cured tobacco leaves outperform in the study. This drying technique is well-established in the tobacco industry and is relatively easy to implement.

Tobacco is primarily used as a raw material for cigarette production. Research into the application of tobacco as biomass has predominantly limited itself to the utilization of tobacco waste. However, we are delighted that the authors can challenge conventional thinking and bring more surprises regarding the potential applications of tobacco. It is also essential to recognize that when tobacco is cultivated for cigarettes, several factors influence the quality of smoking experience. For instance, the recommended planting depth for tobacco seedlings is around 5–8 cm, the distance between the top leaves and the soil surface should be maintained between 1.6 and 3.3 cm, plant spacing should be set at 50–60 cm, and row spacing should be controlled at 110–120 cm. Additionally, effective field management practices are necessary throughout the growth process, which demands considerable human and material resources. However, when tobacco is utilized as biomass, it functions as an energy crop, thereby greatly reducing the need for these specific field management strategies. Although the author's team has acknowledged these distinctions, there has been a lack of practical implementation regarding planting and application. Nevertheless, this insight provided by the researchers has the potential to inspire tobacco growers operating on marginal lands to pursue new possibilities, which could lead to the successful cultivation of tobacco on marginal lands for biorefining, thereby enhancing the utilization of bioenergy resources. Consequently, further experimental efforts should prioritize the cultivation of tobacco on marginal land for biorefinery applications through interdisciplinary cooperation.

The research presented in this article has inspired scientists across various fields, including breeding, cultivation, modern agriculture, and microbiology, fostering collaboration among scientists from different disciplines. This, in turn, can pave the way for exploring the boundless potential future of tobacco, thereby promoting the utilization and development of bioenergy. Furthermore, a deep-going investigation into the efficient industrial-scale utilization of whole tobacco including stems and leaves is crucial for establishing tobacco as a viable energy crop. Tobacco stems have been evaluated as a promising feedstock [6], and the article notes that the proportion of soluble substances in the entire tobacco plant is significant, but the superiority of its application is still lower compared to that of tobacco leaves. Consequently, this study proposes strategies for utilizing tobacco leaves, which should be integrated with existing approaches for using tobacco stems to truly achieve full utilization of tobacco. Moreover, further research should consider the linking characteristics of strains used in growth experiments and bioproducts production to the specific sugar composition and concentrations of tobacco media, which would be invaluable for advancing the biorefinery concept. Additionally, integrating synthetic biology approaches can enhance the engineering of tobacco to accumulate higher levels of water-soluble carbohydrates while removing nicotine and other inhibitors. The application of engineered microorganisms, in conjunction with engineered tobacco plants, can improve the extraction and transformation of biomass into a wider variety of bio-based products, thereby enhancing its value as a feedstock for biorefineries.

Deshui Liu: conceptualization (supporting), investigation (lead), writing–original draft (lead). Xiang Li: investigation (supporting), writing–original draft (supporting). Zhonghao Li: conceptualization (lead), supervision (lead), writing–review and editing (lead).

The authors declare no conflicts of interest.