MreB of Streptomyces coelicolor is not essential for vegetative growth but is required for the integrity of aerial hyphae and spores

Mol Microbiol. 2006 May;60(4):838-52. doi: 10.1111/j.1365-2958.2006.05134.x.

Abstract

MreB forms a cytoskeleton in many rod-shaped bacteria which is involved in cell shape determination and chromosome segregation. PCR-based and Southern analysis of various actinomycetes, supported by analysis of genome sequences, revealed mreB homologues only in genera that form an aerial mycelium and sporulate. We analysed MreB in one such organism, Streptomyces coelicolor. Ectopic overexpression of mreB impaired growth, and caused swellings and lysis of hyphae. A null mutant with apparently normal vegetative growth was generated. However, aerial hyphae of this mutant were swelling and lysing; spores doubled their volume and lost their characteristic resistance to stress conditions. Loss of cell wall consistency was observed in MreB-depleted spores by transmission electron microscopy. An MreB-EGFP fusion was constructed to localize MreB in the mycelium. No clearly localized signal was seen in vegetative mycelium. However, strong fluorescence was observed at the septa of sporulating aerial hyphae, then as bipolar foci in young spores, and finally in a ring- or shell-like pattern inside the spores. Immunogold electron microscopy using MreB-specific antibodies revealed that MreB is located immediately underneath the internal spore wall. Thus, MreB is not essential for vegetative growth of S. coelicolor, but exerts its function in the formation of environmentally stable spores, and appears to primarily influence the assembly of the spore cell wall.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / analysis
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology*
  • Cell Wall / genetics
  • Cell Wall / ultrastructure
  • Gene Deletion
  • Gene Order
  • Green Fluorescent Proteins / analysis
  • Green Fluorescent Proteins / genetics
  • Hyphae / chemistry
  • Hyphae / physiology
  • Hyphae / ultrastructure
  • Microfilament Proteins / analysis
  • Microfilament Proteins / genetics
  • Microfilament Proteins / physiology*
  • Mutation
  • Polymerase Chain Reaction
  • Recombinant Fusion Proteins / analysis
  • Recombinant Fusion Proteins / genetics
  • Spores, Bacterial / chemistry
  • Spores, Bacterial / physiology
  • Spores, Bacterial / ultrastructure
  • Streptomyces coelicolor / chemistry
  • Streptomyces coelicolor / physiology*
  • Streptomyces coelicolor / ultrastructure

Substances

  • Bacterial Proteins
  • Microfilament Proteins
  • Recombinant Fusion Proteins
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins