Application of potential probiotic strain Streptomyces sp. SH5 on anti-Aeromonas infection in zebrafish larvae.

Pre-treatment of Streptomyces sp. SH5 on zebrafish lead to a significant enhancement of larvae survival upon Aeromonas hydrophila challenging. SH5 was able to colonize in zebrafish approximately at 1 × 102.6 cells per fish for at least seven days. The presence of SH5 strongly repelled the A. hydrophila colonization in zebrafish, and maximally, a 67.53% reduction rate was achieved. A more diversified flora was discovered in the SH5-treated zebrafish larvae at both phylum and genus levels. The expression of immune response genes of SH5-treated zebrafish, including TLR3, lysozyme and NOS2α, were enhanced at initial stage, while, that of various inflammatory stimuli genes including 1L-1ß, 1L-6 and MyD88 were decreased at all tested timepoints. SH5 was shown to inhibit virulence factors production and the expression of corresponding virulence genes in A. hydrophila, suggesting its quorum sensing inhibitory potential. These results indicated favorable application perspectives of SH5 in resisting pathogenic infection in aquaculture.

The acetyltransferase SCO0988 controls positively specialized metabolism and morphological differentiation in the model strains Streptomyces coelicolor and Streptomyces lividans.

Streptomycetes are well-known antibiotic producers possessing in their genomes numerous silent biosynthetic pathways that might direct the biosynthesis of novel bio-active specialized metabolites. It is thus of great interest to find ways to enhance the expression of these pathways to discover most needed novel antibiotics. In this study, we demonstrated that the over-expression of acetyltransferase SCO0988 up-regulated the production of specialized metabolites and accelerated sporulation of the weak antibiotic producer, Streptomyces lividans and that the deletion of this gene had opposite effects in the strong antibiotic producer, Streptomyces coelicolor. The comparative analysis of the acetylome of a S. lividans strain over-expressing sco0988 with that of the original strain revealed that SCO0988 acetylates a broad range of proteins of various pathways including BldKB/SCO5113, the extracellular solute-binding protein of an ABC-transporter involved in the up-take of a signal oligopeptide of the quorum sensing pathway. The up-take of this oligopeptide triggers the "bald cascade" that regulates positively specialized metabolism, aerial mycelium formation and sporulation in S. coelicolor. Interestingly, BldKB/SCO5113 was over-acetylated on four Lysine residues, including Lys425, upon SCO0988 over-expression. The bald phenotype of a bldKB mutant could be complemented by native bldKB but not by variant of bldKB in which the Lys425 was replaced by arginine, an amino acid that could not be acetylated or by glutamine, an amino acid that is expected to mimic acetylated lysine. Our study demonstrated that Lys425 was a critical residue for BldKB function but was inconclusive concerning the impact of acetylation of Lys425 on BldKB function.