coli strain derived from K-12, could grow in in M9-TMAO media, whereas the mutants N169-dtatABC and N169-dtatABCE could not grow after being cultured at 37°C for 24 h (Fig. 2). However, when pBAD-TatABC was restored into the mutants N169-dtatABC and pBAD-TatABC Torin 2 was restored into N169-dtatABCE, the complementary strains could grow well in the M9-TMAO media, indicating that the tatABC cluster is essential in the function of the Tat system. N169-dtatE and N169-dtatABC-BCcp could grow in M9-TMAO media, although the OD600 values of these strains were slightly lower than that of N16961 (Fig. 2). In addition, the OD600 of N169-dtatB and N169-dtatC was noticeably lower than that of N16961 in M9-TMAO media

(Fig. 2). Therefore, the tatB and tatC genes appear to be necessary for the V. cholerae Tat system, and tatA and tatE may functionally overlap in V. cholerae. Figure 2 find more growth of V. cholerae tat mutants and complement strains in M9-TMAO media. The OD600 was measured when the strains were cultured at 37°C for 24 h. The OD600 value for each strain was Eltanexor the average of three samples. We also transformed pBAD-TatABC and pBAD-TatE, plasmids containing V. cholerae-derived tatABC and tatE, into the E. coli tat gene mutants [34] to assess if TatA or TatE is essential to Tat system. As shown in Table

2, pBAD-TatABC restored the growth of E. coli tatAE, tatB, tatC, and tatABCDE mutants in M9-TMAO media, whereas pBAD-TatE only restored

the growth of the tatAE mutant. Therefore, V. cholerae tat genes can replace their E. coli counterparts to reconstitute a heterologous functional Tat system. Here it was also shown that tatE, located on chromosome II, may functionally overlap Ergoloid tatA in V. cholerae. The functionality of the Tat system was also confirmed by the subcellular distribution of TMAO reductase activity in the wild type strain N16961, the tatABC mutant strain N169-dtatABC, and strain N169-dtatABC-cp, N169-dtatABC restored with pBAD-TatABC. The prepared fractions of periplasm and cytoplasm were confirmed with the control of western blot assay, using the antibodies to β-lactamase and GroEL. It was shown that β-lactamase was predominantly in the extractd periplasmic fraction, while GroEL was mainly in the extracted cytoplasmic fraction [see Additional file 2]. As anticipated, the TMAO reductase activity was detected in the periplasm of the wild type strain N16961 and N169-dtatABC-cp, but it accumulated in the cytoplasm of N169-dtatABC (Fig. 3). Table 2 Using M9-TMAO media to detect the function of the Tat system in E. coli Tat mutant strains complemented with plasmids containing V. cholerae tat genes Strains pBAD24 pTatABC-301 pBAD-TatABC pBAD-TatE JARV16A (dtatAE) -a + + + MCMTAA(dtatB) – + + – B1LK0A (dtatC) – + + – DADEA(dtatABCDE) – + + – a: “”-”" or “”+”" means no-growth or successful growth of the strain in TMAO minimal media under anaerobic conditions, respectively.