In the few organisms where it has been studied in detail, the single circular chromosome of a rod-shaped bacterium is highly organized and regions of the chromosome have particular subcellular addresses;origins of replication are located at the old cell poles, replication termini are near the new poles derived from cell division. Other loci are arranged in the cell in the order that they appear on the chromosome, origin to terminus. In contrast, the filamentous soil-dwelling bacterium Streptomyces coelicolor has a large linear genome. Little is known about the architecture of the linear chromosome within the Streptomyces spore and the mechanisms which govern its segregation during synchronous division of specialized aerial hyphae are poorly understood. These mycelial organisms are of particular and vital importance to health and biotechnology industries because they produce many biologically active compounds such as antibiotics, antifungals, antihelminthics, herbicides and antitumor drugs. For years researchers have assumed that there is a single copy of the genome per spore compartment of S. coelicolor. Strong preliminary evidence suggests that conventional wisdom is incorrect. First, there is genetic evidence. Mutants of certain genes involved in DNA segregation and condensation appear to produce spores containing DNA that is decondensed showing two lobes of DNA. In addition, apparent genetic diploids can be isolated from the wild type strain. Second, there is cytological evidence. Confocal laser scanning microscopy was used to measure the intensity of fluorescent dye bound to the wild type nucleoid, and the analysis supports the hypothesis of two genome copies per spore. Similarly, preliminary analysis of fluorescent in situ hybridization (FISH) results point to two copies of the genome per wild type spore. Hybridizing a probe to the origin region shows two fluorescent foci located at opposite ends of the spore. Furthermore, a partition protein- EGFP fusion, with binding sites near the origin, localizes in two foci to the poles of maturing spores, as was observed for the origin region using FISH. A candidate gene, encoding a Walker-type ATPase, involved in the establishment of the chromosome position within the spore has been identified. This study proposes experiments to complete the preliminary genetic experiments and extend the cytological analysis of the genome architecture in the spore. Additional genes encoding proteins required for development-associated genome segregation will be identified by bacterial two hybrid analyses. Transcription of several known genes encoding segregation proteins will be tested for their dependence on developmental regulatory genes.
We wish to understand how DNA is segregated and packaged in the special filamentous organisms that produce the majority of biologically active compounds used to treat infection and cancer. These are major producers of the compounds we all rely on for our health and quality of life. Basic knowledge of fundamental cell functions of these organisms may lead to better production of known and novel compounds and lower the cost of buying medicines.
|Santos-Beneit, Fernando; Roberts, David M; Cantlay, Stuart et al. (2017) A mechanism for FtsZ-independent proliferation in Streptomyces. Nat Commun 8:1378|
|McCormick, Joseph R; Flardh, Klas (2012) Signals and regulators that govern Streptomyces development. FEMS Microbiol Rev 36:206-31|