## 1 Introduction
The stoichiometry of _C. necator_'s CO\({}_{2}\) fixation and the growth of necator microorganisms are presented in Equation (1) [31]. Depending on their elemental composition, the experimental formula for the chemical quality of microorganisms is C\({}_{4.08}\)H\({}_{6.87}\)N\({}_{1.0}\)O\({}_{1.89}\)[32]. \[44.25\text{H}_{2}+12.42\text{O}_{2}+8.16\text{CO}_{2}+2\text{NH}_{4}{}^{+} \to 2\text{C}_{4.08}\text{H}_{6.87}\text{N}_{1.0}\text{O}_{1.89}+18.7\text{H} _{2}\text{O}+0.7\text{H}{}^{+} \tag{1}\]  
In many different types of bioreactors, such as stirred-tank bioreactors, hollow-fiber membrane biofilm reactors, or monolithic biofilm reactors, an efficient biological matrix conversion of gas substrates can be performed [33]. Continuous stirred-tank reactors (CSTRs), such as gas lift bioreactors, can be used to increase the volume mass transfer coefficient (K\({}_{\text{L}}\alpha\)), thereby improving substrate utilization, reducing costs, and increasing yields [34]. Although the ratio of the gas mixture has a great influence on the growth rate of bacteria, this interesting aerobic fermentation process offers a favorable bio-carbon capture and utilization (CCU) technology that has great potential for the transition to carbon-neutral plastic manufacturing. However, this interesting aerobic fermentation process remains largely underexploited [35]. The mixture of hydrogen and oxygen can quickly explode, so the characteristics of the bacteria and safety must be considered in the production of SCPs [1]. One of the technical challenges is the formation of an explosive hydrogen-oxygen mixture between O\({}_{2}\) and H\({}_{2}\), with the lower and upper explosion limits of 4.8% and 95.2% H\({}_{2}\), respectively [36]. However, for oxygen, more than a 6 vol% of hydrogen is the lower explosion limit [27]. Therefore, choosing the right bioreactor will be one of the keys to the production of SCPs. Another technical challenge is the dissolved oxygen (dO\({}_{2}\)) concentration, which is called C and considered one of the most critical process parameters in the metabolic culture of necator (and HOBs in general). The conventional method for culturing these bacteria is to direct a gas mixture of CO\({}_{2}\), H\({}_{2}\), and O\({}_{2}\) through a single sparger into a bioreactor containing the bacteria [37]. The simplest, most convenient and effective method for producing hydrogen is water electrolysis, which has an efficiency of around 90% [38]. Choosing the proper fermentation method and operating conditions based on the culture, raw materials, and specific production needs will help optimize the production of SCPs. In this study, the fermentation process was optimized, and different process parameters were investigated, including the amount of secondary seed inoculation, the amount of filler material, and the material itself. These optimization measures are aimed at increasing the fermentation yield under gas conditions. The stability of the continuous gas fermentation process was evaluated. Notably, this study is the first report of the efficient continuous fermentation of SCPs by a self-developed bioreactor under autotrophic conditions. This innovative approach demonstrates great potential for industrial applications and may provide a new, sustainable solution for the production of SCPs. Through further research and optimization, the technology is expected to be widely used in food, feed, and other related fields. The flow diagram of the entire system is shown in Figure 1.