Methanobactin from Methylosinus trichosporium OB3b inhibits N2O reduction in denitrifiers

Abstract

Methanotrophs synthesize methanobactin, a secondary metabolite that binds copper with an unprecedentedly high affinity. Such a strategy may provide methanotrophs a "copper monopoly" that can inhibit the activity of copper-containing enzymes of other microbes, e.g., copper-dependent NO reductases. Here, we show that methanobactin from Methylosinus trichosporium OB3b inhibited NO reduction in denitrifiers. When Pseudomonas stutzeri DCP-Ps1 was incubated in cocultures with M. trichosporium OB3b or with purified methanobactin from M. trichosporium OB3b, stoichiometric NO production was observed from NO reduction, whereas no significant NO accumulation was observed in cocultures with a mutant defective in methanobactin production. Copper uptake by P. stutzeri DCP-Ps1 was inhibited by the presence of purified methanobactin, leading to a significant downregulation of nosZ transcription. Similar findings were observed with three other denitrifier strains. These results suggest that in situ stimulation of methanotrophs can inadvertently increase NO emissions, with the potential for increasing net greenhouse gas emissions.

Metals and Methanotrophy

“…Further, when P. stutzeri DCP-Ps1 was incubated in the presence of a mutant of M. trichosporium OB3b incapable of expressing MB, N 2 O production trends were identical to those of axenic cultures of P. stutzeri DCP-Ps1. Similar findings were found with three other denitrifiers that express NosZ (92). As methanotrophs and denitrifiers can and do spatially overlap in the environment, these findings indicate that competition for copper may significantly affect net greenhouse gas emissions in situ.…”

“…Microbial competition for copper is regulated by methanobactin. Given that methanobactin binds copper with extraordinarily high affinity, Chang et al (92) hypothesized that methanotrophs, through the production of methanobactin, could effectively "starve" other microbes for copper. Specifically, denitrifying microbes also require substantial amounts of copper for the activity of the nitrous oxide reductase NosZ (93).…”

“…Indeed, when axenic cultures of the denitrifier Pseudomonas stutzeri DCP-Ps1 were examined, very small and transient amounts of N 2 O were observed (ϳ0.01% of added NO 3 Ϫ ). When P. stutzeri DCP-Ps1 was incubated either in the presence of M. trichosporium OB3b or purified MB from this methanotroph (MB-OB3b), all added NO 3 Ϫ was converted to N 2 O, with no further reduction (92). Further, when P. stutzeri DCP-Ps1 was incubated in the presence of a mutant of M. trichosporium OB3b incapable of expressing MB, N 2 O production trends were identical to those of axenic cultures of P. stutzeri DCP-Ps1.…”

“…In addition, copper competition between methanotrophs and other microbes may limit the activity of other copper-dependent enzymes, e.g., the nitrite reductase NirK and ammonia monooxygenase (93,97). Indeed, it has been found that methanobactin can inhibit the activity of NirK in Shewanella loihica (92). Additional work in this area is clearly warranted.…”

Trace metal availability affects greenhouse gas emissions and microbial functional group abundance in freshwater wetland sediments

“…It could be that the mcrA response was not as 299 strong due to insufficient time to increase in abundance (Enzmann et al, 2018). Another interesting aspect 300 of Cu effects on CH 4 emissions is the competition between methanotrophs and denitrifiers for the "Cu 301 monopoly" (Chang et al, 2018), which should be further investigated in environmental samples. Thus, the higher abundance of methanogens (mcrA) and noticable accumulation of CH 4 in all metal treatments than 303 the control indicates an important role of trace metal availability in CH 4 cycling in environmental samples.…”