Two TonB-Dependent Transporters in Methylosinus trichosporium OB3b Are Responsible for Uptake of Different Forms of Methanobactin and Are Involved in the Canonical “Copper Switch”

Abstract

In this study, we demonstrate that different TBDTs in the model methanotroph Methylosinus trichosporium OB3b are responsible for uptake of either endogenous MB or exogenous MB. Interestingly, the presence of exogenous MB induces expression of its specific TBDT in M. trichosporium OB3b, suggesting that this methanotroph is able to actively take up MB produced by others.

Multiple Mechanisms for Copper Uptake by Methylosinus trichosporium OB3b in the Presence of Heterologous Methanobactin

“…mbnT2 was significantly downregulated in the presence versus the absence of copper (~3-fold; P < 0.05) in M. trichosporium wild type. mbnT2 , however, was upregulated (90- to 290-fold; P < 0.01) in M. trichosporium OB3b wild type when grown in the presence of copper (1 μM) and MB-SB2 (5 μM) compared to the absence or presence of copper ( 34 ) ( Fig. 3d ).…”

“…In an earlier study ( 34 ), we identified a second MB uptake system (mediated by MbnT2) in M. trichosporium OB3b that is responsible for uptake of heterologous MB produced from Methylocystis sp. SB2 and determined that the expression of mbnT2 is induced by MB-SB2.…”

“…Due to the similar structure of MbnT1 and MbnT2, as well as the genetic organization of the mbnT1 and mbnT2 gene clusters, it is reasonable to speculate that binding of MB-OB3b to MbnT1 should also generate a signal to release MbnI1 and thereby initialize transcription of MbnT1. However, unlike MbnT2, MbnT1 expression is not controlled by MB-OB3b ( 34 ). Rather, MbnT1 is constitutively expressed.…”

“…The mechanism of MB excretion is believed (but not conclusively shown) to occur via a multidrug export pump encoded by mbnM . MB uptake has been much more extensively characterized, with a TonB-dependent transporter (TBDT, encoded by mbnT ) shown to be critical for reinternalization ( 32 – 34 ). In general, TBDTs consist of two conserved domains: one a barrel domain that forms the basic/main structure and the other a plug domain that is folded into the barrel interior ( 35 ).…”

“…Previously, it has been demonstrated that M. trichosporium OB3b has two MB uptake systems mediated by MbnT1 and MbnT2 responsible for uptake of homologous and heterologous MBs (MB-OB3b and MB-SB2), respectively ( 32 – 34 ). In this study, we demonstrate that M. trichosporium OB3b can take up copper from heterologous MB-SB2 via two different approaches.…”