Response of a methane-driven interaction network to stressor intensification.

Microorganisms may reciprocally select for specific interacting partners, forming a network with interdependent relationships. The methanotrophic interaction network, comprising methanotrophs and non-methanotrophs, is thought to modulate methane oxidation and give rise to emergent properties beneficial for the methanotrophs. Therefore, microbial interaction may become relevant for community functioning under stress. However, empirical validation of the role and stressor-induced response of the interaction network remains scarce. Here, we determined the response of a complex methane-driven interaction network to a stepwise increase in NH4Cl-induced stress (0.5-4.75 g L-1, in 0.25-0.5 g L-1 increments) using enrichment of a naturally occurring complex community derived from a paddy soil in laboratory-scale incubations. Although ammonium and intermediates of ammonium oxidation are known to inhibit methane oxidation, methanotrophic activity was unexpectedly detected even in incubations with high ammonium levels, albeit rates were significantly reduced. Sequencing analysis of the 16S rRNA and pmoA genes consistently revealed divergent communities in the reference and stressed incubations. The 16S rRNA-based co-occurrence network analysis revealed that NH4Cl-induced stress intensification resulted in a less complex and modular network, likely driven by less stable interaction. Interestingly, the non-methanotrophs formed the key nodes, and appear to be relevant members of the community. Overall, stressor intensification unravels the interaction network, with adverse consequences for community functioning. © FEMS 2020.