Introduction. Methane (CH4) is the second most abundant greenhouse gas. Compared to carbon dioxide, methane is more potent at absorbing radiation and trapping heat into the atmosphere. Significant reduction in atmospheric CH4 levels could have a rapid impact on lowering global temperatures. Sustainable mitigation of global methane levels can be achieved via microbial methane utilization. Furthermore, methane-based technology has the potential to produce valuable compounds, such as fuels and chemicals. However, methane oxidation requires other elements such as oxygen, sulfur species, nitrogen species or metals to drive the process. The sulfur, nitrogen, and metals are too expensive. Although oxygen is abundant in the environment, pure oxygen is an expensive feedstock for industrial application. Moreover, the use of pure oxygen-methane mixtures is dangerous. Thus, biotechnological applications require further developments of an efficient system for intracellular oxygen cycling and generation. Oxygen cycling system. Microbes have evolved dedicated oxygen carrier molecules such as bacteriohemerythrin (Bhr), which deliver O2 to cytochrome C-oxidase for respiration. It has been proposed that the function of bacteriohemerythrin in methanotrophic bacteria is to transport oxygen to the particulate methane monooxygenase (pMMO) for methane oxidation. However, the role of Bhr in the context of live bacterial cells remains to be explored. Here, the consequences of the overexpression and deletion of Bhr on aerobic methane oxidation in Methylotuvimicrobium alcaliphilum (20ZR) were investigated. The data suggest that Bhr does not impact methane oxidation, and rather contributes to oxygen-dependent respiration. Intracellular oxygen production. Of the three known pathways for biological oxygen production, light-dependent oxygen production (photosynthesis) is the most prominent and well-studied. The machinery of light-dependent water split is complex and includes up to 30 proteins. In this study, novel genetic construct for integration and tunable expression of the core genes of PSII (psbA and psbD) system into M. alcaliphilum 20ZR genome were constructed. This work represents the first step for assembling PSII system, and constructing methanotrophic traits capable of intracellular PSII-mediated water hydrolysis for intracellular oxygen production.