## 2 Limitations of Conventional Bioformulation and the Development of Bioencapsulation  
Bioformulation is biologically defined as all active products containing one or more beneficial microbes or their metabolites and which are immobilized on an inert carrier material [4]. The microbe is a living organism and considered a bioagent and can be either a single strain, a spore, or a microbial consortium [5]. Several microorganisms are used to develop bioformulations, namely, bacteria, actinobacteria, and fungi [5]. The carrier material is an inactive material and serves as a carrier of the living organism, providing a protective niche. This carrier must be nontoxic, be chemically stable, be readily available, be inexpensive, be able to maintain humidity, ensure the viability of cells during storage, and ensure their transport close to the target plant [6]. The medium used can be organic (soil, peat, coal, etc.) or inorganic (polymers), solid or liquid [3]. Alongside the support and the living organism, bioformulations may also contain additives, such as starch and humic acid, which provide nutritional support to the formulated microorganisms [7]. Whether solid or liquid, conventional bioformulation has been for a long time the technology of choice for the development of bioinoculants [8]. On a practical level, the techniques are easy to develop, and the materials used are most often available [3]. Solid bioformulations are made by mixing the beneficial microorganism with a solid carrier, which is used as a vehicle. Peat is the preferred carrier in this type of formulation. With its large surface area, high water retention capacity, and composition, it provides a favorable environment for metabolic activity and cell multiplication during storage [5]. However, peat compounds can affect the development of certain microorganisms [9]. Besides peat, various other media are used, such as biochar, bagasse, cork compost, atapulgite, sepiolite, perlite, and amorphous silica [3; 10]. Solid bioformulations include granules, microgranules, wettable powders (WPs), wettable granules (WGs)/water dispersible granules (WDGs), and dusts [5]. Liquid bioformulations are usually microbial suspensions in water, in oil, or sometimes in both [11]. This type of formulation allows the formulated microorganisms to quickly come into contact with the target plant and exert their beneficial actions there. However, the absence of the support makes it sensitive to contamination and to prolonged storage conditions and periods [3]. Besides the carrier liquid and the microorganism, dispersing agents and surfactants can be added to the formulations in order to improve their physicochemical quality [12]. Suspension concentrates, oil miscible flowable concentrates, ultra-low-volume suspensions, and oil dispersions are the most reported types of liquid bioformulations [5]. Liquid bioformulations are applied directly to seeds, while solid bioformulations are even applied as a soil amendment [13]. Due to the high demand for bioinoculants based on PGPMs in the agricultural sector and in order to overcome the limitations linked to conventional bioformulations (solid and liquid), science has moved towards the development of new formulations, ensuring better viability, more high stability during storage and transport, ease of use, and better performance in the field [14]. Not only that, these formulations must guarantee the success of the application under extreme conditions, such as saline, acidic, or alkaline soils; high temperatures; and drought [14]. Immobilized formulations of PGPMs in polymers or encapsulation are an advanced, promising, and rapidly developing technology that has significant advantages over other formulations. Encapsulation tends to cover living cells with a polymer matrix that serves as a microenvironment that protects cells and their metabolites from adverse external conditions. This process is also called immobilization. Comobilization is when multiple strains are applied [3].