Soil desertification is a major challenge in global environmental issues, referring to the process of land degradation and gradual loss of productivity due to various natural and human factors. China is one of the countries most severely affected by soil desertification. According to data from the State Forestry and Grassland Administration of China, approximately 27% of the country's land area is threatened by desertification [1]. The main reasons include overgrazing, unreasonable agricultural activities, deforestation, and climate change. Especially in the northwest and northern regions of China, the impact of desertification is particularly significant, leading to the deterioration of local ecosystems and the deterioration of living conditions for residents.

On a global scale, soil desertification is equally severe. The United Nations Convention to Combat Desertification (UNCCD) states that approximately 30% of the world's land is affected by desertification, and the amount of arable land lost each year due to soil degradation is equivalent to one Ukrainian national territory [2]. The global rate of soil desertification is astonishing, posing a huge threat to ecosystems and human survival. According to the report of the United Nations Convention to Combat Desertification (UNCCD), approximately 12 million hectares of land are lost each year due to desertification, which is equivalent to approximately 23 football fields per minute [2].

Figure 1. Global data on desertification risk (The dataset is provided by National Cryosphere Desert Data Center, http://www.ncdc.ac.cn)

Global soil desertification is an increasingly serious environmental problem that has far-reaching impacts on ecosystems and human society. According to the United Nations Environment Programme (UNEP), approximately 25% of the world's land area is affected by desertification, involving 110 countries and approximately 1 billion people [3]. The impact of soil desertification on the ecological environment is enormous. Healthy soil is an important component of maintaining plant growth, regulating water circulation, and storing carbon. When soil degradation occurs, plant cover decreases, leading to a decrease in biodiversity. Research has shown that a decrease in biodiversity in soil can lead to a decrease in ecosystem service functions, such as water filtration, nutrient cycling, and climate regulation. In addition, land lacking vegetation is more susceptible to wind and water erosion, further exacerbating soil erosion and forming a vicious cycle.

Approximately 200 million people worldwide rely directly on land affected by desertification for agricultural production. As farmland becomes barren, food production decreases, leading to food security issues. Especially in sub–Saharan Africa and Central Asia, desertification has led to significant population displacement and intensified conflicts. In addition, the shortage of water resources is exacerbated by soil degradation, which further affects human survival and development. According to data from the Food and Agriculture Organization of the United Nations (FAO), the annual economic losses caused by desertification worldwide reach up to $42 billion [4].

The global problem of soil desertification requires comprehensive management methods. Planting trees and restoring vegetation are the most common measures. According to a report by the United Nations Environment Programme (UNEP), afforestation can significantly reduce soil erosion and improve soil fertility [3]. However, combating desertification faces many challenges. Firstly, the economic costs are high, especially for developing countries, implementing large-scale governance projects requires a significant amount of funding and technical support [2]. In addition, climate change has intensified the difficulty of governance, and extreme weather and changes in precipitation patterns have made soil restoration more complex. Therefore, how to reduce the cost of afforestation, or rather, how to improve the efficiency of afforestation and ensure that the planting of trees is efficient is the question we want to explore.

Water retention refers to the ability of soil to retain moisture. Soil with high water retention can slowly release water, providing continuous water sources for plants and significantly improving vegetation survival rate. Soil with poor water retention is prone to rapid drying after precipitation, resulting in insufficient water supply to plant roots. Research has shown that in arid areas, improving soil water retention can increase vegetation survival rates by more than 50% [5]. By increasing the water content of the roots of newly planted vegetation, the survival rate of vegetation can be effectively improved, and the cost and difficulty of desert management can be reduced.

BC is a valuable extracellular biopolymer synthesized by several bacteria belonging to the genera Acetobacter, Komagataeibacter, Agrobacterium, Bacillus, Clostridium botulinum, Lactobacillus, and Bacillus glucoses [6]. The nanofibrous network constituting the BC structure consists of well-aligned three-dimensional nanofibers forming a high surface area and porous hydrogel layer [7]. During cellulose synthesis, protofibrils are released from the bacterial cell wall and assembled into bundles to form nanofibrils with BC highly porous network structure. Then, the nanofibers form a skin layer on the surface of the medium [8].

Unlike plant cellulose, BC can be obtained purely from the culture medium and actively excreted by the cells without a complex purification process as it is free of lignin, hemicellulose, pectin, arabinose, and other plant-derived contaminants. BC has excellent physicochemical and mechanical properties such as purity, high crystallinity, high water storage capacity, high degree of polymerization, high surface area, and chemical stability. In addition, BC is biocompatible, biodegradable, and renewable compared to other water retention materials such as Hydrogel, Polyacrylamide (PAM), Sodium carboxymethyl cellulose (CMC) [6].

The demand for BC has increased considerably due to its excellent properties. Komagataeibacter xylinus belongs to the group of strains that are natural producers of BC with much higher yields than other strains and is a model organism for the study of BC. In the past, researchers have focused on the production of BC using low-cost substrates, investigating potential BC producers, optimizing culture conditions, and modifying the structure of BC particles using different methods [6]. These strategies were mostly at the macro level, and research on how to improve BC production using molecular biology methods has only increased in the last two years due to the completion of whole genome sequencing.

Most cellulose acetate-producing strains can convert glucose to gluconic acid and ketogluconic acid extracellularly. The enzyme responsible for the conversion of glucose to gluconic acid is membrane-bound glucose dehydrogenase (GDH) [9]. The production of gluconic acid will reduce the amount of glucose in the medium and affect the production of cellulose. Comparative studies have been carried out and some isolates that are more capable of producing cellulose from glucose have been found to have lower GDH activity [10].

In the biosynthetic pathway of bacterial cellulose, in the presence of glucose-6-phosphate isomerase (PGI), fructose 6-phosphate can be catalysed to produce glucose 6-phosphate, which is promising to enhance the metabolic flow of BC production [11]. In summary, we plan to enhance BC production by overexpressing the pgi gene and knocking out the gdh gene in Komagataeibacter xylinus.

Figure 2. Bacterial cellulose biosynthesis diagram