## 1 Introduction  
Bacterial cellulose (BNC) is known as a material of unique properties. It is synthesized by many bacteria, such as _Komagataeibacter_, _Sarcina_, _Agrobacteriumium_, and _Rhizobium_[1]. The most widely studied are the _Komagataeibacter_ (former _Gluconacetobacter_) species, which produce the chemical pure polymer efficiently without lignin or hemicelluloses, compared to the plant cellulose. BNC has a gelatinous consistency and consists of ultrathin fibers having a width of about 8 nm and a length of approximately 50-80 nm which form a three-dimensional network. Bacterial cellulose is characterized by a high crystallinity which is over 85% and an excellent mechanical strength. Due to its physicochemical properties, BNC can be used in the food industry, acoustic diaphragms, high-strength paper products, and enzyme or drug immobilization. The water holding capacity up to 99% and the biocompatibility of bacterial cellulose make BNC highly attractive for medical applications, such as wound dressing [2], temporary skin substitute [3], artificial blood vessels [4], and scaffold for tissue engineering [5]. Bacterial cellulose biosynthesis yield, its morphology, and physical properties could be influenced by choosing culture methods. Under shaking conditions, BNC accumulates as spheres or pellets in the medium, while in a static culture a pellicle is formed [6]. A BNC membrane is synthesized layer by layer at the air/medium interface by bacterial cells [7], which are present in the aerobic zone of the synthesized BNC [8]. Although both of these culturing methods are commonly employed in various target productions, the majority of applications, especially in medicine and the cosmetic industry, demand a definite shape of cellulosic materials, such as thin membranes, sheets, or tubes. So far, only static culture meets this requirement [9]. It is important to understand the chemical, biological, and physical factors, which can influence the course of biosynthesis and properties of BNC [6; 10]. Numerous papers describe the optimization of the BNC yield with different methods. The most common approach is one-factor-at-a-time method where only one factor is changing in a series of experiments. Also, the statistical optimization methods are used increasingly often, e.g., the Plackett-Burman design (PBD) [11; 12], the central composite design (CCD) [11; 12; 13; 14], or the factorial design (FD) [15], which require less experiments and show the global impact of variables on studied responses. On the other hand, there is a lack in mechanical properties study in terms of different culture conditions. Numerous studies in the past revealed that various additives in situ or ex situ, such as carboxymethylcellulose [16; 17], poly-3-hydroxybutyrate [18], poly (vinyl alcohol) [19], \(\kappa\)-carrageenan [5], polysiloxane, and fluorocarbon polymers [20] or polyethylene glycol diacrylate [21] can affect the structure of BNC leading to changes in tensile strength. However, only a few reports are available which discuss the impact of common culture conditions. [PERSON] et al. studied the effect of different strains, cultivation time, and surface to volume ratio on mechanical properties, but the authors used only two levels for each variable [22]. The present work is focused on a detailed analysis of relationship between culture condition and both the yield and tensile strength. For this purpose, we designed a surface air-flow (SAF) bioreactor set and determined the factors affecting the BNC dry weight using the Plackett-Burman design. Based on statistical analysis, six factors were chosen for further investigation, namely the air-flow ratio, volume and age of inoculum, pH, glucose concentration, and cultivation time. We assessed the impact of these factors on the yield and mechanical properties, such as strain, stress, and Young modulus. The obtained data allow definition of the rational area of input factor variability in static culture of _K. xylinus_ E25.