Introduction Methanotrophs, defined as aerobic methane-oxidizing bacteria, utilize methane as a sole carbon and energy source; thus, they have an important role in the global carbon cycle [1, 2]. Methane monooxygenase (MMO) is the key enzyme for acting as a methanotroph because it oxidizes methane to methanol. Due to its low specificity, MMO can oxidize different recalcitrant compounds such as alkanes and aromatic hydrocarbons [3-5]. Therefore, methanotrophs are broadly used as biocatalysts in many biotechnological processes, such as in biodegradation systems for methane as a greenhouse gas and recalcitrant contaminants [6, 7]. Most methanotrophs have been considered to be obligate to methane, but some are facultative methanotrophs that can utilize multi-carbon compounds including ethanol and organic acids, such as acetate, pyruvate, and malate [8, 9]. Methanotrophs have been commonly encountered in natural environments such as oceans, fresh waters, wetlands, and soils [1, 2, 9]. They have been reported to be closely associated with various organisms such as plants, protists, and marine invertebrates as well as with other bacteria [1, 10, 11]. For instance, methanotrophs have synergistic interactions with sphagnum mosses and microalgae by exchanging CO 2 and O 2 [12-14]. They are reported to be endosymbionts of marine invertebrates [10], and also prey for bacterivores [15]. Therefore, it is probable that methanotrophs significantly interact with many other biotic components in different ways. There are different types of microbial interactions, some of which can be beneficial to at least one participant, e.g., commensalism, synergism, mutualism, parasitism, and predation [16]. Recent reports indicate that methanotrophic activity can be enhanced by commensalism and synergism
