Exploring new avenues of growth and secondary metabolite production by antibiotic-producing Streptomyces bacteria

• Applicant: Dr. Tina Netzker
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; Microbial Ecology and Applied Microbiology
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418836285

• Final Report Year: 2022

Final Report Abstract

The genus Streptomyces, which contains the largest number of known species within the domain bacteria, is of major scientific interest due to their extraordinary life cycle and their prolific secondary metabolism. Recently, it was shown that the model organism Streptomyces venezuelae can escape from its classical life cycle when confronted with fungi or a nutrientpoor environment, using a newly described growth behaviour called exploration. Explorer cells grow much more rapidly than classically-growing cells, and the resulting ‘motile’ colony adopts a complex architecture that is reminiscent of biofilms in other bacterial systems. To understand the underlying molecular and genetic basis of exploratory growth we examined the role of nucleotide second messengers cAMP, c-di-GMP, and (p)ppGpp during exploration. We have found that a Crp mutant fails to explore and this is independent of increased cAMP concentrations. Screening of S. venezuelae mutants deficient in either synthesis or degradation of c-di-GMP revealed the diguanylate cyclase CdgB and the phosphodiesterase RmdB as being the most important for exploratory growth. Analysis of c-di-GMP concentrations during exploration revealed constant c-di-GMP concentrations in the wildtype and increased levels during early exploration in the crp and cdgB mutant strains. Overexpression of cdgB in the crp deletion mutant restored wildtype-like exploration, confirming a link between the two. In parallel, we discovered that the (p)ppGpp synthetase RelA is the major (p)ppGpp producer in S. venezuelae and that a relA deletion mutant explores faster than the wildtype, which suggests that (p)ppGpp may function to inhibit early exploration. RNAseq analysis of the relA mutant strain revealed ramC as one of the most upregulated genes. ramC belongs to an operon, required for production of the surfactant SapB. We hypothesise that SapB promotes rapid colony spread through its surfactant activity; further experimental analyses will provide insight into its role during exploration.

Publications

• (2020). Bacterial volatile compounds: Functions in communication, cooperation, and competition. Annu Rev Microbiol 74, 409-430
  Netzker T, Shepherdson EMF, Zambri MP, Elliot MA
  
• (2020). Lichen-like association of Chlamydomonas reinhardtii and Aspergillus nidulans protect algal cells from bacteria. ISME J 14 (11), 2794-2805
  Krespach MKC, García-Altares M, Flak M, Schoeler H, Scherlach K, Netzker T, Schmalzl A, Mattern DJ, Schroeckh V, Komor A, Mittag M, Hertweck C, Brakhage AA
  
• (2020). Targeted induction of silent fungal gene cluster encoding the bacteria-specific germination inhibitor fumigermin. eLife 9, e52541
  Stroe MC, Netzker T, Scherlach K, Krüger T, Hertweck C, Valiante V, Brakhage AA
  
• (2021) Exploratory growth in Streptomyces venezuelae involves a unique transcriptional program, enhanced oxidative stress response, and profound acceleration in response to glycerol
  Shepherdson EMF, Netzker, T, Stoyanov, Y, Elliot MA