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TCID	Name	Domain	Kingdom/Phylum	Protein(s)
1.B.14.1.1	FhuE ferric-coprogen receptor of 729 aas and 1 N-terminal TMS. It is required for the uptake of Fe³⁺ via coprogen, ferrioxamine B, and rhodotorulic acid (Hantke 1983). The crystal structure of FhuE in complex with coprogen was determined, providing a structural basis to explain its selective promiscuity (Grinter and Lithgow 2019). The structural data, in combination with functional analysis, showed that FhuE has evolved to specifically engage with planar siderophores. A potential evolutionary driver, and a critical consequence of this selectivity, is that it allows FhuE to exclude antibiotics that mimic nonplanar hydroxamate siderophores. These toxic molecules could otherwise cross the outer membrane barrier through a Trojan horse mechanism (Grinter and Lithgow 2019).	Bacteria	Pseudomonadota	FhuE of E. coli
1.B.14.1.2	FhuA ferrichrome (also albomycin and rifamycin; Colicin M; Microcin J25; Phage T5) receptor (transports phage T1, T5 and φ80 DNA across the outer membrane, dependent on DcrA (SdaC; TC #2.A.42.2.1) and DcrB) (Forms a complex with and acts with TonB and FhuD (the periplasmic binding receptor (3.A.1.14.3) to deliver siderophore to FhuD (Carter et al., 2006; Braun et al., 2009)). Deletion of the 160-residue cork domain and five large extracellular loops converted this non-conductive, monomeric, 22-stranded beta-barrel protein into a large-conductance protein pore (Wolfe et al. 2015). FhuA and its various applications indicate that it is a versatile building block to generate hybrid catalysts and materials (Sauer et al. 2023).	Bacteria	Pseudomonadota	FhuA of E. coli
1.B.14.1.3	Ferric enterobactin (also ferricorynebactin) receptor, IroN	Bacteria	Pseudomonadota	IroN of Salmonella typhimurium
1.B.14.1.4	CirA Fe³⁺-catecholate receptor. Serves as the receptor for the TonB- and proton-dependent uptake of the E. coli bacteriocin, Microcin L (MccL) (Morin et al., 2011). CirA is also the translocator for colicin Ia (Jakes and Finkelstein, 2010). Plays roles in cefiderocol and ceftazidime resistance (Ito et al. 2018). Genotypic evolution of Klebsiella pneumoniae sequence type 512 during Ceftazidime/Avibactam, Meropenem/Vaborbactam, and Cefiderocol treatment. This occurred through plasmid loss, outer membrane porin alteration, and a nonsense mutation in the cirA siderophore gene, resulting in high levels of cefiderocol resistance (Arcari et al. 2023).	Bacteria	Pseudomonadota	CirA of E. coli
1.B.14.1.5	PfeA ferric enterobactin receptor	Bacteria	Pseudomonadota	PfeA of Pseudomonas aeruginosa
1.B.14.1.6	Ferripyoverdine/pyocin S3 receptor, FpvA (Adams et al., 2006; Nader et al., 2007; Schalk et al., 2009; Nader et al., 2011)	Bacteria	Pseudomonadota	FpvA of Pseudomonas aeruginosa
1.B.14.1.7	Iron malleobactin receptor, FmtA (Alice et al., 2006)	Bacteria	Pseudomonadota	FmtA of Burkholderia pseudomallei (EBA51007)
1.B.14.1.8	The Ferripyochelin receptor, FptA (Michel et al., 2007). In addition to Fe³⁺, FptA takes up Co²⁺, Ga³⁺, and Ni²⁺ at low rates (Braud et al., 2009). The high resolution 3-d structure of FptA (2.0 Å) bound to iron-pyochelin has been solved (Cobessi et al. 2005). The pyochelin molecule provides atetra-dentate coordination of iron. The structure is typical of the TonB-dependent receptor/transporter superfamily.	Bacteria	Pseudomonadota	FptA of Pseudomonas aeruginosa (P42512)
1.B.14.1.9	Ferric-catecholate siderophore (dihydroxybenzoylserine, dihydroxybenzoate) uptake receptor, Fiu or YbiL (Hantke, 1990; Curtis et al., 1988). Plays roles in cefiderocol and ceftazidime resistance (Ito et al. 2018). It can also transport catechol-substituted cephalosporins and is a receptor for microcins M, H47 and E492 (Patzer et al. 2003; Destoumieux-Garzón et al. 2006).	Bacteria	Pseudomonadota	Fiu of E. coli (P75780)
1.B.14.1.10	The outer membrane ferrioxamine/desferrioxamine receptor, FoxA(1) (most like TC# 1.B.14.1.4 and 9) (Wei et al., 2007)	Bacteria	Pseudomonadota	FoxA(1) of Nitrosomonas europaea (Q82VI7)
1.B.14.1.11	The outer membrane ferric-anguibactin receptor/transporter, FatA (Lopez and Crosa, 2007)	Bacteria	Pseudomonadota	FatA of Vibrio anguillarum (P11461)
1.B.14.1.12	FecA ferric-citrate receptor (PA3901) (Marshall et al., 2009) (62% identical to the E. coli FecA).	Bacteria	Pseudomonadota	FecA of Pseudomonas aeruginosa (Q9HXB2)
1.B.14.1.13	CfrA ferric receptor (Carswell et al., 2008).	Bacteria	Campylobacterota	CfrA of Campylobacter jejuni (A3ZKG8)
1.B.14.1.14	Ferric-pseudobactin 358 receptor	Bacteria	Pseudomonadota	PupA of Pseudomonas putida
1.B.14.1.15	Ferrichrome receptor FcuA	Bacteria	Pseudomonadota	FcuA of Yersinia enterocolitica
1.B.14.1.16	Probable TonB-dependent receptor BfrD (Virulence-associated outer membrane protein Vir-90)	Bacteria	Pseudomonadota	BfrD of Bordetella pertussis
1.B.14.1.17	Ferrioxamine receptor, FoxA. Transports a variety of Ferrioxamine B analogues (Kornreich-Leshem et al. 2005).	Bacteria	Pseudomonadota	FoxA of Yersinia enterocolitica
1.B.14.1.18	TonB-dependent receptor (Bhat et al. 2011).	Bacteria	Myxococcota	TonB-dependent receptor of Myxococcus xanthus
1.B.14.1.19	TonB-dependent receptor	Bacteria	Myxococcota	TonB-dependent receptor of Myxococcus xanthus
1.B.14.1.20	The iron-citrate receptor/transporter, FecA. TonB mediates both signaling and transport by unfolding portions of the transporter (Mokdad et al. 2012). The ferric citrate regulator, FecR, is translocated across the bacterial inner membrane via a unique Twin-arginine transport dependent mechanism (Passmore et al. 2020).	Bacteria	Pseudomonadota	FecA of E. coli
1.B.14.1.21	Ferrioxamine receptor	Bacteria	Pseudomonadota	Ferrioxamine receptor of Pseudovibrio sp. JE062
1.B.14.1.22	FepA ferri-enterobactin (also Colicins B and D) receptor for the 37 aas disulfide-containing K⁺ channel toxin, BgK (Braud et al., 2004). Functions by a "ball and chain" mechanism; The transport process involves expulsion of the N-terminal globular domain from the C-terminal beta-barrel (Ma et al. 2007). Conformational rearrangements occur in the N-terminus of FepA during FeEnt transport, but disengagement of the N-domain, out of the rigid channel suggests that it remains within the transmembrane pore as FeEnt enters the periplasm (Majumdar et al. 2020).	Bacteria	Pseudomonadota	FepA of E. coli
1.B.14.1.23	OMR of 938 aas	Bacteria	Myxococcota	OMR of Myxococcus xanthus
1.B.14.1.24	Putative TonB-dependent siderophore receptor, Sde_3611	Bacteria	Pseudomonadota	Sde3611 of Saccharophagus degradans
1.B.14.1.25	Nickel uptake receptor/channel of 724 aas (Benoit et al. 2013).	Bacteria	Campylobacterota	HH0418 of Helicobacter hepaticus
1.B.14.1.26	Iron siderophore (ferripyoverdine) receptor and importer, FpvA of 808 aas (Ye et al. 2014). The crystal structure of FpvA has been solved at 3.6 Å resolution. It is folded in two domains: a transmembrane 22-stranded beta-barrel domain occluded by an N-terminal domain containing a mixed four-stranded beta-sheet (the plug). The beta-strands of the barrel are connected by long extracellular loops and short periplasmic turns (Cobessi et al. 2005).	Bacteria	Pseudomonadota	FpvA of Pseudomonas aeruginosa
1.B.14.1.27	Iron(III) dicitrate transport protein, FecA1: iron dicitrate uptake receptor of 767 aas. Regulated by the ferric uptake regulator transcription factor, Fur (van Vliet et al. 2002) in response to iron availability (Danielli et al. 2009). Involved in iron deficiency anemia in children (Kato et al. 2017).	Bacteria	Campylobacterota	FecA1 of Helicobacter pylori
1.B.14.1.28	FecA3 of 843 aas. Probable receptor for nickel. Shows 50% identiy with TC# 1.B.14.1.27. Repressed by nickel in the medium, mediated by NikR (Danielli et al. 2009). NikR seems to interact in an asymmetric mode with the fecA3 target to repress its transcription (Romagnoli et al. 2011).	Bacteria	Campylobacterota	FecA3 of Helicobacter pylori
1.B.14.1.29	Iron-deficiency-induced (2x) iron siderophore uptake outer membrane receptor, FhuA, of 828 aas and 1 N-terminal TMS (Qiu et al. 2018).	Bacteria	Cyanobacteriota	FhuA of Synechocystis sp. (strain PCC 6803 / Kazusa)
1.B.14.1.30	Outer membrand iron siderophore uptake receptor of 853 aas and 1 N-terminal TMS, Slr1490.	Bacteria	Cyanobacteriota	Slr1490 of Synechocystis sp. (strain PCC 6803 / Kazusa)
1.B.14.1.31	Outer membrane porin, PiuA, of 753 aas. A deficiency of this iron transporter, PiuA in P. aeruginosa, caused 16-fold increases in cefiderocol resistance, suggesting that it contribute to the permeation of cefiderocol into the cell (Ito et al. 2018).	Bacteria	Pseudomonadota	PiuA of Pseudomonas aeruginosa
1.B.14.1.32	Catechol iron-siderophore uptake system, IrgA, an iron-regulated outer membrane virulence protein, of 652 aas and 1 N-terminal TMS (Wyckoff et al. 2015). It is involved in the initial step of iron uptake by binding ferric vibriobactin, an iron chelatin siderophore that allows V. cholerae to extract iron from the environment and takes up linear enterobactin derivatives (Wyckoff et al. 2015).	Bacteria	Pseudomonadota	IrgA of Vibrio cholerae
1.B.14.1.33	Heme/hemin outer membrane TonB-related receptor of 708 aas, Tlr (Slakeski et al. 2000).	Bacteria	Bacteroidota	Tlr of Porphyromonas gingivalis
1.B.14.2.1	HmbR Hemoglobin receptor	Bacteria	Pseudomonadota	HmbR of Neisseria meningitidis
1.B.14.2.2	HemR Heme (Hemin) receptor	Bacteria	Pseudomonadota	HemR of Yersinia enterocolitica
1.B.14.2.3	HpuAB hemoglobin-haptoglobin receptor; porphyrin transporter (HpuA=lipoprotein; HpuB=OMR porin). Surface exposed loops in the gonococcal HpuB transporter are important for hemoglobin binding and utilization (Awate et al. 2023).	Bacteria	Pseudomonadota	HpuAB of Neisseria meningitidis
1.B.14.2.4	Lactoferrin receptor (A=OMR porin; B=lipoprotein), LbpAB or IroAB. This two-component system extracts iron from the host glycoproteins lactoferrin and transferrin. Homologous iron-transport systems consist of a membrane-bound transporter and an accessory lipoprotein. The crystal structure of the N-terminal domain (N-lobe) of the accessory lipoprotein, lactoferrin-binding protein B (LbpB) is homologous to the structures of the accessory lipoproteins, transferrin-binding protein B (TbpB) and LbpB from the bovine pathogen Moraxella bovis. Docking the LbpB with lactoferrin reveals extensive binding interactions with the N1 subdomain of lactoferrin. The nature of the interaction precludes apolactoferrin from binding LbpB, ensuring the specificity for iron-loaded lactoferrin, safeguarding proper delivery of iron-bound lactoferrin to the transporter LbpA. The structure also reveals a possible secondary role for LbpB in protecting the bacteria from host defences. Following proteolytic digestion of lactoferrin, a cationic peptide derived from the N-terminus is released. This peptide, called lactoferricin, exhibits potent antimicrobial effects. The docked model of LbpB with lactoferrin reveals that LbpB interacts extensively with the N-terminal lactoferricin region (Brooks et al. 2014).	Bacteria	Pseudomonadota	LbpAB of Neisseria meningitidis
1.B.14.2.5	TbpA single component transferrin receptor	Bacteria	Pseudomonadota	TbpA of Pasteurella multocida
1.B.14.2.6	HugA heme receptor/porin	Bacteria	Pseudomonadota	HugA of Plesiomonas shigelloides (Q93SS7)
1.B.14.2.7	Hemin (Heme)-binding receptor, ShmR (also transports the toxic heme analog, gallium protoporphyrin) (Amarelle et al., 2008).	Bacteria	Pseudomonadota	ShmR of Sinorhizobium meliloti (Q92N43)
1.B.14.2.8	The heme-iron (from hemin and hemoglobin) utilization receptor, BhuR (Brickman et al., 2006; Vanderpool and Armstrong, 2004).	Bacteria	Pseudomonadota	BhuR of Bordetella pertussis (Q7VSQ4)
1.B.14.2.9	Probable TonB-dependent receptor NMB0964	Bacteria	Pseudomonadota	Y964 of Neisseria meningitidis MC58
1.B.14.2.10	Heme transporter BhuA (Brucella heme uptake protein A)	Bacteria	Pseudomonadota	BhuA of Brucella abortus
1.B.14.2.11	Heme/hemopexin utilization protein C	Bacteria	Pseudomonadota	HxuC of Haemophilus influenzae
1.B.14.2.12	The transferrin receptor/lipoprotein complex, TbpAB (TbpA receptor, 912aas; TbpB lipoprotein, 625aas). The plug domain can fold independently of the beta-barrel, but extracellular loops of the beta-barrel are required for ferritin binding (Oke et al. 2004).	Bacteria	Pseudomonadota	TbpAB of Haemophilus influenzae TbpA (P44970) TbpB (P44971)
1.B.14.2.13	Hemoglobin receptor, HgbA. Residues for hemoglobin binding and utilization differ (Fusco et al. 2013).	Bacteria	Pseudomonadota	HgbA of Haemophilus ducreyi
1.B.14.2.14	Heme/hemoglobin receptor of 660 aas and 22 C-terminal β-strands with an N-terminal "plug" domain, ShuA. The 3-d structure is known to 2.6 Å resolution, revealing the histidyl residues in the barrel and plug that can interact with heme (Cobessi et al. 2010).	Bacteria	Pseudomonadota	ShuA of Shigella dysenteriae
1.B.14.2.15	Uncharacterized outer membrane receptor, probably for iron transport.	Bacteria	Pseudomonadota	OMR of Xanthomonas oryzae
1.B.14.2.16	Transferrin binding protein A, TbpA of 914 aas. A 3-D model revealed a narrow channel through the entire length of the protein. The spatial arrangement of external loops, and their relevance to the mechanism of iron translocation is presented (Oakhill et al. 2005).	Bacteria	Pseudomonadota	TbpA of Neisseria meningitidis
1.B.14.2.17	The iron-catechol siderophore uptake/receptor, VctA, of 659 aas. Linear enterobactin derivatives are substrates, but it also transports the synthetic siderophore MECAM [1,3,5-N,N',N″-tris-(2,3-dihydroxybenzoyl)-triaminomethylbenzene] (Wyckoff et al. 2015).	Bacteria	Pseudomonadota	VctA of Virbio cholerae
1.B.14.3.1	BtuB cobalamin receptor (also transports phage C1 DNA across the outer membrane). Two Ca²⁺ binding sites in BtuB mediate cobalamine binding (Cadieux et al., 2007). Cobalamine uptake into the periplasm is reversible, but efflux is pmf-independent (Cadieux et al., 2007). The 3-d structure is available (PDB#1NQE). The Ton box and the extracellular substrate binding site are allosterically coupled (bidirectional), and TonB binding may initiate a partial round of transport (Sikora et al. 2016). Substrate binding to the extracellular surface of the protein triggers the unfolding of an energy coupling motif at the periplasmic surface. Thus, substrate binding reduces the interaction free energy between certain residues, thereby triggering the unfolding of the energy coupling motif (Lukasik et al. 2007). Multiple extracellular loops contribute to substrate binding and transport by BtuB (Fuller-Schaefer and Kadner 2005).	Bacteria	Pseudomonadota	BtuB of E. coli
1.B.14.3.2	TonB-dependent receptor (Bhat et al. 2011).	Bacteria	Myxococcota	TonB-dependent receptor of Myxococcus xanthus
1.B.14.3.3	TonB-dependent receptor (Bhat et al. 2011).	Bacteria	Myxococcota	TonB receptor of Myxococcus xanthus
1.B.14.3.4	TonB-dependent receptor (Bhat et al. 2011).	Bacteria	Myxococcota	TonB-dependent receptor of Myxococcus xanthus
1.B.14.3.5	TonB-dependent receptor (Bhat et al. 2011).	Bacteria	Myxococcota	TonB-dependent receptor of Myxococcus xanthus
1.B.14.3.6	Probable siderophore-specific outer membrane receptor of 869 aas, MxcH	Bacteria	Myxococcota	MxcH of Stigmatella aurantiaca
1.B.14.3.7	TonB-dependent receptor	Bacteria	Pseudomonadota	OMR of Shewanella oneidensis
1.B.14.4.1	Cu²⁺-transporting, Cu²⁺-regulated outer membrane protein C, OprC (Yoneyama and Nakae 1996). OprC impairs host defense by increasing the quorum-sensing-mediated virulence of P. aeruginosa (Gao et al. 2020).	Bacteria	Pseudomonadota	OprC of Pseudomonas aeruginosa
1.B.14.4.2	Cu²⁺-transporting, outer membrane protein, NosA	Bacteria	Pseudomonadota	NosA of Pseudomonas stutzeri
1.B.14.4.3	TonB-dependent receptor/channel for substrate uptake across the outer membrane of 656 aas	Bacteria	Pseudomonadota	Receptor of E. coli
1.B.14.5.1	HasR receptor-HasA haemophore heme receptor complex (HasA, an extracellular heme binding protein, binds one heme and transfers it directly to HasR, which uses HasB (2.C.1.1.2) (a TonB homologue) instead of TonB (2.C.1.1.1) for energization) (Benevides-Matos et al., 2008; Izadi-Pruneyre et al., 2006; Lefèvre et al., 2008; Benevides-Matos and Biville, 2010). A signaling domain in HasR interacts with a partially unfolded periplasmic domain of an antisigma factor, HasS, to control transcription by an ECF sigma factor (Malki et al. 2014). The HasR domain responsible for signal transfer is highly flexible in two stages of signaling, extends into the periplasm at about 70 to 90 A from the HasR beta-barrel and exhibits local conformational changes in response to the arrival of signaling activators (Wojtowicz et al. 2016).	Bacteria	Pseudomonadota	HasR-HasA of Serratia marcescens
1.B.14.5.2	The heme receptor HxuC (PA1302) serves as a pyocin M4 (Colicin M-type; PaeM4) target at the cellular surface.	Bacteria	Pseudomonadota	HxuC of Pseudomonas aeruginosa
1.B.14.6.1	SusC receptor/porin for maltooligosaccharides (up to maltoheptaose). Forms a complex with and functions with SusD porin (TC# 8.A.46.1.1) as well as SusE and SusF porins (TC#s 1.B.38.1.1 and 1.2) as well as the SusG α-amylase (TC#8.A.9.1.3). These proteins are all involved in starch utilization (Shipman et al. 2000; Reeves et al. 1997; Cho and Salyers 2001; Foley et al. 2018).	Bacteria	Bacteroidota	SusC of Bacteroides thetaiotaomicron
1.B.14.6.2	The Omp200 porin complex (consists of Omp121 [an OMR family member] and Omp71 [a protein nonhomologous to other proteins in the databases])	Bacteria	Bacteroidota	Omp121/Omp71 complex of Bacteroides fragilis
1.B.14.6.3	Outer membrane porin required for intercellular signalling via C-signal (CsgA), Oar (Bhat et al. 2011).	Bacteria	Myxococcota	Oar of Myxococcus xanthus
1.B.14.6.4	TonB-dependent outer membrane porin/receptor, Oar	Bacteria	Pseudomonadota	Oar of Stenotrophomonas maltophila
1.B.14.6.5	TonB-dependent outer membrane receptor of 792 aas.	Bacteria	Bacteroidota	TonB receptor of Bacteroides caccae
1.B.14.6.6	TonB-dependent receptor of 970 aas	Bacteria	Spirochaetota	TonB receptor of Leptospira interrogans
1.B.14.6.7	TonB-dependent receptor	Bacteria	Bacteroidota	TonB receptor of Pedobacter heparinus
1.B.14.6.8	Putative OMR (DUF4480) of 709 aas and one N-terminal TMS. The first 120 residues show sequence similarity with TC#1.B.14.6.2.	Bacteria	Bacteroidota	Putative OMR of Bacteroides fragilis
1.B.14.6.9	Putative OMR (DUF4480) of 828 aas, and N-terminal TMS and 32 predicted TM β-strands.	Bacteria	Bacteroidota	Putative OMR of Croceibacter atlanticus
1.B.14.6.10	DUF4480 putative OMR of 835 aas.	Bacteria	Bacteroidota	OMR of Capnocytophaga canimorsus
1.B.14.6.11	OMR (DUF4480) of 976 aas	Bacteria	Bacteroidota	OMR of Zobellia galactanivorans
1.B.14.6.12	OMR (DUF4480) of 775 aas	Bacteria	Bacteroidota	OMR of Saprospira grandis
1.B.14.6.13	SusC homologue of 940 aas. Functions with SusD homolgoue TC# 8.A.46.1.2.	Bacteria	Bacteroidota	SusC homologue of Bacteroides thetaiotaomicron
1.B.14.6.14	Putative porin of 830 aas and 16 predicted TMSs. The β-barrel domain is the N-terminal ~250 aas which corresponds to the DUF4480 or Peptidase M14NE family in Pfam. The large hydrophilic C-terminal domain is of unknown function.	Bacteria	Bacteroidota	Putative porin of Aequorivita sublithincola
1.B.14.6.15	TonB-dependent collagenase (proteinase) of 1047 aas (Bhattacharya et al. 2017). The primary pathogen of the Great Barrier Reef sponge, Rhopaloeides odorabile, identified as a unique strain (NW4327) of Pseudoalteromonas agarivorans. It produces collagenases which degrade R. odorabile skeletal fibers.	Bacteria	Proteobacteria	Collagenase of Pseudoalteromonas agarivolans NW4327 (a marine sponge parasite)
1.B.14.6.16	Possible Iron receptor, RagA of 1036 aas. Its gene forms part of a small operon which may have arisen via horizontal gene transfer into the genome. The 55 kDa antigen (RagB; TC# 8.A.46.3.5), encoded within the same operon, may act in concert at the surface of the bacterium to facilitate active transport, mediated through the periplasmic spanning protein, TonB (Curtis et al. 1999).	Bacteria	Bacteroidota	RagAB of Porphyromonas gingivalis
1.B.14.6.17	SusC of 1041 aas and 1 N-terminal TMS (Joglekar et al. 2018).	Bacteria	Bacteroidota	SusC of Bacteroides thetaiotaomicron
1.B.14.6.18	TonB-dependent receptor/transporter of 909 aas	Bacteria	Acidobacteriota	Receptor of Granulicella mallensis
1.B.14.7.1	CjrC outer membrane receptor of 753 aas. It is iron and temperature regulated, and functions with CjrB, a distant TonB homologue (TC# 2.C.1.1.3). Together these two proteins are required for uptake of colicin J in Shigella and enteroinvasive E. coli strains (Smajs and Weinstock 2001).	Bacteria	Pseudomonadota	CjrC of E. coli
1.B.14.7.2	Probable TonB-dependent receptor NMB1497	Bacteria	Pseudomonadota	NMB1497 of Neisseria meningitidis
1.B.14.7.3	Probable TonB-dependent receptor HI_1217	Bacteria	Pseudomonadota	HI_1217 of Haemophilus influenzae
1.B.14.8.1	Putative salicin/arbutin (aromatic β-glucoside) receptor, SalC	Bacteria	Pseudomonadota	SalC of Azospirillum irakense
1.B.14.8.2	The iron (Fe³⁺) · pyridine-2,6-bis(thiocarboxylic acid) (PDTC) receptor, PdtK. Functions with the MFS carrier, PdtE (TC #2.A.1.55.1) (Leach and Lewis, 2006).	Bacteria	Pseudomonadota	PdtK of Pseudomonas putida (ABC68350)
1.B.14.8.3	Vibriobactin receptor, VuiA or VuuA of 687 aas and 1 N-terminal TMS. There is conserved, global coordinate iron regulation in V. cholerae by the Fur transcription factor, responsive to iron (Butterton et al. 1992). V. cholerae synthesizes and uses the catechol siderophore vibriobactin and also uses siderophores secreted by other species, including enterobactin produced by E. coli (Wyckoff et al. 2015). ViuB, a putative V. cholerae siderophore-interacting protein (SIP), functionally substituted for the E. coli ferric reductase YqjH, which promotes the release of iron from the siderophore in the bacterial cytoplasm. In V. cholerae, ViuB is required for the use of vibriobactin but is not required for the use of MECAM, fluvibactin, ferrichrome, or the linear derivatives of enterobactin, all substrates of ViuA (Wyckoff et al. 2015).	Bacteria	Pseudomonadota	ViuA of Vibrio cholerae serotype O1
1.B.14.8.4	The thiamine receptor (SO2715) (energized by TonB/ExbBD) (Rodionov et al. 2002)	Bacteria	Pseudomonadota	SO2715 of Shewanella oneidensis (Q8EDM8)
1.B.14.8.5	TonB-dependent receptor of 726 aas.	Bacteria	Pseudomonadota	Receptor of Colwellia psychrerythraea
1.B.14.8.6	The (thio)quinolobactin receptor, QbsI, of 669 aa	Bacteria	Pseudomonadota	QbsI of Pseudomonas fluorescens
1.B.14.8.7	FyuA Fe³⁺-yersiniabactin and pesticin (Psn; a bacteriocin) receptor and uptake protein of 673 aas. It contributes to biofilm formation and infection (Hancock et al., 2008). It is similar to FrpA, an outer membrane protein involved in piscibactin secretion in Vibrio anguillarum (Lages et al. 2022).	Bacteria	Pseudomonadota	FyuA of Yersinia enterocolitica (P0C2M9)
1.B.14.9.1	RhtA Rhizobactin 1021 (siderophore) receptor/porin	Bacteria	Pseudomonadota	RhtA of Sinorhizobium meliloti
1.B.14.9.2	Acr ferric achromobactin (hydroxycarboxylate siderophore) receptor/porin (Franza et al., 2005)	Bacteria	Pseudomonadota	Acr of Erwinia chrysanthemi (AAL14566)
1.B.14.9.3	The ferric ferrichrome/aerobactin receptor/porin, IutA (Forman et al., 2007)	Bacteria	Pseudomonadota	IutA of Yersinia pestis (Q7CGN6)
1.B.14.9.4	Putative TonB-dependent heme receptor	Bacteria	Campylobacterota	TonB-dependent heme receptor of Campylobacter jejuni
1.B.14.9.5	TonB-dependent receptor of 700 aas, YncD, a probable iron transporter/receptor in the outer membrane. Deletion of the orthologous yncD genes in Salmonella strains leads to attenuated strains, potentially useful for vaccine development (Xiong et al. 2012; Xiong et al. 2015). Its synthesis is depressed by inclusion of high glucose concentrations in the medium (Yang et al. 2011). YncD is a receptor for a T1-like Escherichia coli phage named vB_EcoS_IME347 (IME347) (Li et al. 2018).	Bacteria	Pseudomonadota	YncD of E. coli
1.B.14.9.6	SchT (IutA) is capable of using dihydroxamate xenosiderophores, either ferric schizokinen (FeSK) or a siderophore of the filamentous cyanobacterium Anabaena variabilis ATCC 29413 (SAV), as the sole source of iron in a TonB-dependent manner (Obando S et al. 2018). Functions with the ABC uptake system having the TC# 3.A.1.14.24.	Bacteria	Cyanobacteriota	SchT of Synechocystis sp. PCC 6803
1.B.14.10.1	Heme/hemoglobin receptor, HmuR (also binds the Cu²⁺, Zn²⁺ and Fe²⁺ derivatives of protoporphyrin IX). Functions with the O.M. heme binding lipoprotein, HmuY (AAQ66587; Olczak et al., 2007).	Bacteria	Bacteroidota	HmuR of Porphyromonas gingivalis
1.B.14.10.2	TonB-dependent receptor	Bacteria	Myxococcota	TonB receptor of Myxococcus xanthus
1.B.14.10.3	TonB-dependent receptor	Bacteria	Myxococcota	TonB recpetor of Myxocuccus xanthus
1.B.14.10.4	Putative TonB-dependent receptor	Bacteria	Cyanobacteriota	OMR of Gloeobacter violaceus
1.B.14.10.5	Probable TonB-dependent long chain alkane receptor of 699 aas (Gregson et al. 2018).	Bacteria	Pseudomonadota	TonB-dependent receptor of Thalassolituus oleivorans
1.B.14.10.6	Cobalt cation concentration sensitive Btu-like system, Btu1, of 698 aas and 1 N-terminal TMS. It facilitates cobalamin uptake in Anabaena sp. PCC 7120 (Graf et al. 2024). The regulation by cobalt and cobalamin as well as their uptakes are described for Anabaena sp. PCC 7120, a model filamentous heterocyst-forming cyanobacterium. Anabaena contains at least three cobalamin riboswitches in its genome, for one of which the functionality was confirmed (Graf et al. 2024). Two outer membrane-localized cobalamin TonB-dependent transporters, namely BtuB1 and BtuB2, were identified. BtuB2 is important for fast uptake of cobalamin under conditions with low external cobalt, whereas BtuB1 appears to function in cobalamin uptake under conditions of sufficient cobalt supply. While the general function is comparable, the specific function of the two genes differs and mutants thereof show distinct phenotypes. The uptake of cobalamin depends further on the TonB and a BtuFCD machinery, as mutants of tonB3 and btuD show reduced cobalamin uptake rates.	Bacteria	Cyanobacteriota	BtuB1 of Anabaena sp. PCC 7120
1.B.14.11.1	The Nickel (Ni²⁺) receptor (FrpB4; Hp1512) of 877 aas. Energized by the TonB/ExbBD complex (Schauer et al., 2007). Capable of binding both haem and haemoglobin but shows greater affinity for haem. The mRNA levels of frpB1 were repressed by iron and lightly modulated by haem or haemoglobin. Overexpression of the frpB1 gene supported cellular growth when haem or haemoglobin were supplied as the only iron source (Carrizo-Chávez et al. 2012).	Bacteria	Campylobacterota	FrpB4 of Helicobacter pylori (Q9ZJA8)
1.B.14.12.1	The TonB-dependent maltooligosaccharide OM receptor/porin, MalA (Lohmiller et al., 2008).	Bacteria	Pseudomonadota	MalA of Caulobacter crescentus (Q9A608)
1.B.14.12.2	The N-acetyl glucosamine/chitin oligosaccharide OM receptor porin, NagA (Eisenbeis et al., 2008).	Bacteria	Pseudomonadota	NagA of Caulobacter crescentus (Q9AAZ6)
1.B.14.12.3	TonB-dependent receptor	Bacteria	Myxococcota	TonB-dependent receptor of Myxococcus xanthus
1.B.14.13.1	TonB-dependent receptor of 763 aas	Bacteria	Pseudomonadota	Receptor of Xanthomonas campestris
1.B.14.14.1	The thiamine receptor (BT2390) (energized by TonB/ExbBD) (Rodionov et al. 2002).	Bacteria	Bacteroidota	BT2390 of Bacteroides thetaiotaomicron (Q8A552)
1.B.14.15.1	Putative porin of the DUF4289 family; 655 aas and 32 putative transmembrane beta strands.	Bacteria	Bacteroidota	PP of Psychroflexus torquis
1.B.14.15.2	Putative porin of 776 aas	Bacteria	Bacteroidota	PP of Provotella ruminicola
1.B.14.15.3	Putative porin of 631 aas	Bacteria	Bacteroidota	PP of Amoebophilus asiaticus
1.B.14.15.4	Putative DUF4289 family porin of 687 aas	Bacteria	Bacteroidota	PP of Niastella koreensis
1.B.14.15.5	Putative porin of 627 aas	Bacteria	Ignavibacteriota	PP of Melioribacter roseus
1.B.14.15.6	Putative porin of 650 aas	Bacteria	Ignavibacteriota	PP of Ignavibacterium album
1.B.14.15.7	Putative porin of 621 aas	Bacteria	Bacteroidota	PP of Cryptocercus punctulatus
1.B.14.16.1	DUF940 homologue of 720 aas, one signal sequence and 30 putative β-strands. Homologous to proteins designated YmcA, WbfB and YjbH.	Bacteria	Chlamydiota	DUF940 homologue of Protochlamydia amoebophila
1.B.14.16.2	DUF940 homologue of 953 aas, one N-terminal signal sequence and 30 putative beta strands.	Bacteria	Pseudomonadota	DUF940 homologue of Chromobacterium violaceum
1.B.14.16.3	DUF940 homologue of 689 aas, one N-terminal signal sequence and 28 putative TM β-strands.	Bacteria	Pseudomonadota	DUF940 homologue of Psychromonas ingrahamii
1.B.14.16.4	DUF940 homologue of 940 aas, one N-terminal signal sequence and 32 putative TM β-strands.	Bacteria	Pseudomonadota	DUF940 homologue of E. coli
1.B.14.16.5	DUF940 homologue of 716 aas with one N-terminal signal sequence and 27 putative beta strands.	Bacteria	Chlamydiota	DUF940 homologue of Parachlamydia acanthamoebae
1.B.14.16.6	DUF940 homologue of 718 aas, an N-terminal signal sequence and 33 putative beta strands.	Bacteria	Pseudomonadota	DUF940 homologue of Photobacterium angustum
1.B.14.16.7	Putative polysaccharide exporter of 690 aas and 34 predicted TMSs, WbfB. Encoded in a gene cluster with polysaccharide biosynthetic enzymes and a putative periplasmic polysaccharide export protein.	Bacteria	Thermodesulfobacteriota	Putative OMR concerned with polysaccharide export of Syntrophus aciditrophicus
1.B.14.16.8	Putative polysaccharide/glycolipid/glycoprotein export receptor of 736 aas and 30 predicted β-strands, WbfB. The gene encoding this protein is in a cluster with UDP-N-acetyl D-quinovosamine -4 epimerase.	Bacteria	Pseudomonadota	Putative exporter of Vibrio anguillarum
1.B.14.16.9	Putative lipopolysaccharide export receptor, WbfB. It is encoded in a gene cluster with LPS biosynthetic genes.	Bacteria	Pseudomonadota	WbfB of Vibrio parahaemolyticus
1.B.14.16.10	Putative LPS exporter receptor, OtuG. It's gene is in a cluster with several LPS biosynthetic enzymes.	Bacteria	Pseudomonadota	OtuG of Vibrio parahaemolyticus
1.B.14.16.11	OMR of 698 aas and 1 N-terminal TMS, GlfD or YmcA. Probably involved in capsular polysaccharide export (Peleg et al. 2005).	Bacteria	Pseudomonadota	GlfD of E. coli
1.B.14.17.1	Uncharacterized protein of 922 aas	Bacteria	Bacteroidota	UP of Dyadobacter fermentans
1.B.14.17.2	Putative Planctomycetes OMR of 799 aas	Bacteria	Planctomycetota	Putative OMR of Planctomyces brasiliensis
1.B.14.17.3	Putative Planctomycetes OMR of 1101 aas	Bacteria	Planctomycetota	Putative OMR of Isosphaera pallida
1.B.14.17.4	Uncharacterized protein of 1055 aas	Bacteria	Lentisphaerota	UP of Lentisphaera araneosa
1.B.14.18.1	Putative Verucomicrobial OMP of 676 aas	Bacteria	Verrucomicrobiota	Putative OMR of Optutus terrae
1.B.14.18.2	Uncharacterized OM channel superfamily member of 791 aas	Bacteria	Verrucomicrobiota	UP of Pedosphaera parvula
1.B.14.19.1	Putative TonB-dpenedent receptor of 790 aas, YddB. It is encoded by a gene adjacent to the YddA-encoding gene (TC# 3.A.1.203.11). YddA is a probable fatty acid exporter. the yddB gene is adjacent to a gene encoding a putative Zn²⁺ protease, PqqL.	Bacteria	Pseudomonadota	YddB of E. coli
1.B.14.19.2	TonB-dependent receptor of 843 aas.	Bacteria	Pseudomonadota	Receptor of Rhodobacter capsulatus
1.B.14.19.3	TonB-dependent receptor/transporter of 834 aas.	Bacteria	Verrucomicrobiota	Receptor of Verrucomicrobiaceae bacterium