The gene coding for nigrescin produced by Prevotella nigrescens ATCC 25261

Aim:  To identify the gene that encodes nigrescin, a bacteriocin produced by Prevotella nigrescens ATCC 25261.
Methods and Results:  Each open reading frame (ORF) of the nig gene cluster ( nigA, nigB, nigC and nigD ) was transferred into an expression vector. The recombinant proteins encoded by nigA, nigB, nigC and nigD were purified and assayed for bacteriocin activity against Porphyromonas gingivalis . The ORFs of the nig gene cluster in Pr. nigrescens ATCC 25261 were re-analysed. It revealed that the position of nig ORFs was similar to previously designated locations, except that the start codon of nigC was reassigned. The new nigC gene started at the nucleotide base position 2454 and stopped at position 3608 (the position designated is relative to the first nucleotide base of the nig locus) and putatively encoded a protein with a predicted molecular mass of 41·9 kDa. The N-terminal 6xHistidine-tag recombinant proteins of NigA, NigB, NigC and NigD were overexpressed in Escherichia coli BL21 star (DE3) and were purified using Ni-NTA resins. Only recombinant NigC showed inhibitory activity against P. gingivalis A244 with minimal inhibition concentration (MIC) of 40 μg ml⁻¹.
Conclusion:  These results indicate that nigC is the gene that encodes nigrescin.
Significance and Impact of the study:  This is the first report that indicates that the gene nigC codes for nigrescin, a bacteriocin produced by Pr. nigrescens ATCC 25261.