Deletion of TerD-domain-encoding genes: effect on Streptomyces coelicolor development

A terD domain-encoding gene (SCO2368) is involved in calcium homeostasis and participates in calcium regulation of a DosR-like regulon in Streptomyces coelicolor

Although Streptomyces coelicolor is not resistant to tellurite, it possesses several TerD domain-encoding (tdd) genes of unknown function. To elucidate the function of tdd8, the transcriptomes of S. coelicolor strain M145 and of a tdd8 deletion mutant derivative (the Δtdd8 strain) were compared. Several orthologs of Mycobacterium tuberculosis genes involved in dormancy survival were upregulated in the deletion mutant at the visual onset of prodiginine production. These genes are organized in a putative redox stress response cluster comprising two large loci. A binding motif similar to the dormancy survival regulator (DosR) binding site of M. tuberculosis has been identified in the upstream sequences of most genes in these loci. A predicted role for these genes in the redox stress response is supported by the low NAD(+)/NADH ratio in the Δtdd8 strain. This S. coelicolor gene cluster was shown to be induced by hypoxia and NO stress. While the tdd8 deletion mutant (the Δtdd8 strain) was unable to maintain calcium homeostasis in a calcium-depleted medium, the addition of Ca(2+) in Δtdd8 culture medium reduced the expression of several genes of the redox stress response cluster. The results shown in this work are consistent with Tdd8 playing a significant role in calcium homeostasis and redox stress adaptation.

Acinetobacter baylyi long-term stationary-phase protein StiP is a protease required for normal cell morphology and resistance to tellurite

We investigated the Acinetobacter baylyi gene ACIAD1960, known from previous work to be expressed during long-term stationary phase. The protein encoded by this gene had been annotated as a Conserved Hypothetical Protein, surrounded by putative tellurite resistance ("Ter") proteins. Sequence analysis suggested that the protein belongs to the DUF1796 putative papain-like protease family. Here, we show that the purified protein, subsequently named StiP, has cysteine protease activity. Deletion of stiP causes hypersensitivity to tellurite, altered population dynamics during long-term batch culture, and most strikingly, dramatic alteration of normal cell morphology. StiP and associated Ter proteins (the StiP-Ter cluster) are therefore important for regulating cell morphology, likely in response to oxidative damage or depletion of intracellular thiol pools, triggered artificially by tellurite exposure. Our finding has broad significance because while tellurite is an extremely rare compound in nature, oxidative damage, the need to maintain a particular balance of intracellular thiols, and the need to regulate cell morphology are ubiquitous.