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A novel lanC-like sequence was identified from the dominant human gut bacterium Blautia obeum strain A2-162. This sequence was extended to reveal a putative lantibiotic operon with biosynthetic and transport genes, two sets of regulatory genes, immunity genes, three identical copies of a nisin-like lanA gene with an unusual leader peptide, and a fourth putative lanA gene. Comparison with other nisin clusters showed that the closest relationship was to nisin U. B. obeum A2-162 demonstrated antimicrobial activity against Clostridium perfringens when grown on solid medium in the presence of trypsin. Fusions of predicted nsoA structural sequences with the nisin A leader were expressed in Lactococcus lactis containing the nisin A operon without nisA. Expression of the nisA leader sequence fused to the predicted structural nsoA1 produced a growth defect in L. lactis that was dependent upon the presence of biosynthetic genes, but failed to produce antimicrobial activity. Insertion of the nso cluster into L. lactis MG1614 gave an increased immunity to nisin A, but this was not replicated by the expression of nsoI. Nisin A induction of L. lactis containing the nso cluster and nisRK genes allowed detection of the NsoA1 pre-peptide by Western hybridization. When this heterologous producer was grown with nisin induction on solid medium, antimicrobial activity was demonstrated in the presence of trypsin against C. perfringens, Clostridium difficile and L. lactis. This research adds to evidence that lantibiotic production may be an important trait of gut bacteria and could lead to the development of novel treatments for intestinal diseases.

A previously reported gene cluster encoding four nisin-like peptides, three with the same sequence (NsoA1-3) and the unique NsoA4, produced antimicrobial activity in the presence of trypsin after heterologous expression in Lactococcus lactis. Protein extracts were separated by SDS gel electrophoresis or immunoprecipitation using an antibody to the NsoA2 leader. Tryptic peptides observed by LC-MS/MS covered the complete sequence of preNsoA1-3 and part of the leader sequence of preNsoA4 and confirmed the expression and the predicted sequences of the preNsoA peptides. Further, the data revealed that the preNsoA1-3 peptides were partly modified with dehydrations and formation of lanthionine rings. A certain amount of fully modified preNsoA1-3 was observed. Details of modifications of the core peptide and the C-terminal tryptic peptide TATCGCHITGK covering rings D and E indicated that 22% of these preNsoA1-3 peptides were completely modified. A lower amount of ring formation is estimated for rings A-C. Intact masses of immunoprecipitation-derived peptides determined by LC-MS accurately matched the expected preNsoA precursor peptides. The most abundant peptides detected were preNsoA2-3-8H2O followed by preNsoA1-8H2O and other states of dehydration. The results confirm incomplete processing of preNsoA peptides in the heterologous system, with the formation of a certain amount of fully modified peptides.