Award details

Coordination of chromosome segregation and hyphal growth in Streptomyces coelicolor

Reference	BB/D521657/1
Principal Investigator / Supervisor	Dr Paul Herron
Co-Investigators / Co-Supervisors
Institution	University of Strathclyde
Department	Bioscience
Funding type	Research
Value (£)	221,103
Status	Completed
Type	Research Grant
Start date	01/11/2005
End date	31/10/2008
Duration	36 months

Abstract

The integration of DNA replication, segregation and cell division in combination with other cellular processes is fundamental to the growth of any organism. This proposal describes a programme aimed at understanding the coordination of chromosome segregation with hyphal growth and cytokinesis in the bacterium, S. coelicolor. Not only are streptomyces one of the most commercially important groups of bacteria, producing over 70 per cent of antibiotics, but they are also among the most unusual: they have a linear chromosome and grow by means of multinucleate vegetative hyphae, before differentiating to form unigenomic spores. As a result, comparison of streptomycete cell division mechanisms with those of unicellular bacteria may well shed light on the fundamental practices shared between all prokaryotes. Recent work, in other laboratories, has suggested that streptomycetes differ from many other bacteria in that their growth appears to be monodirectional and occurs primarily by incorporation of peptidoglycan at the hyphal tip. However, earlier studies indicated that peptidoglycan is also incorporated along the hyphal walls. In other bacteria, bidirectional chromosome segregation can be accommodated within the latter mode of cell wall synthesis and thus contained within a mechanism for cell division by binary fission. Unless streptomycetes possess a novel system for chromosome positioning, segregation and division site selection, it is not possible to reconcile bidirectional chromosome segregation with monodirectional hyphal extension. However, recent work by the applicant suggests that streptomycete cell division is actually more similar to other bacteria than previously imagined and indicates the existence of a primary cellular positioning mechanism. In order to resolve this apparent paradox I intend to demonstrate unequivocally the manner in which streptomycetes segregate daughter chromosomes and incorporate cell wall material in growing hyphae. In recent years the study of complex processes in streptomycetes has become more tractable following the implementation of advanced genomic techniques. Despite this, the mechanisms of chromosome segregation and cell division are still not understood in streptomycetes. I aim to characterise these processes and complement these techniques by developing strains and imaging systems that will allow the coordination of chromosome segregation with hyphal growth and cytokinesis to be studied in Streptomyces. This will be done by the microscopic analysis of fixed cells using fluorescent in situ hybridisation, tagging of key cell division proteins with GFP and localisation of sites of murein incorporation in cell walls. In addition I will also tag the S. coelicolor chromosome with fluorescence reporter operator systems to allow chromosome segregation of individual hyphal lineages to be tracked by time lapse microscopy and a precise order of the key events during cell division described.

Summary

Streptomyces are an unusual and commercially important group; they are filamentous and form a tangled mass of hyphae before sporulating. They also make over 70 per cent of naturally produced antibiotics. The aim of this research is to characterise streptomycete growth and cell division which will allow us to design improvements to strains and processes to generate increased yields of antibiotics through enhanced growth or better morphology of the organism. Cell division is a process that is required for proliferation of all organisms. In rod shaped bacteria, cell division occurs after cell growth by addition of new material along the walls, but not at the ends of the cell. This causes lengthening of the cell away from the cell¿s equator in both directions. Eventually a point is reached where DNA replication is triggered and the two copies of the chromosome are moved towards opposite ends of the cell. At the centre of the cell, a crosswall is laid down and divides the mother cell into two daughter cells, each containing a copy of the chromosome. Recent work has made it possible to explain how the movement of daughter chromosomes to opposite ends of the cell is coordinated with growth of the cell in both directions. This is a highly complex and coordinated procedure; for the cell to successfully divide, each component of the cell division process must be directed to the correct cellular address at the appropriate time. Under normal circumstances, each streptomycete hyphal compartment contains many chromosomes, so only occasionally is DNA replication linked with the formation of a cross wall. Streptomyces grow in one direction only by extension of the hyphal tip and, following DNA replication, daughter chromosomes are able to populate the extending tip by an unknown mechanism. It is the aim of this research to characterise this mechanism. Streptomycetes can also divide by sporulation where a ladder of cross walls is laid down along a hyphal compartment. This divides the hypha into a string of spores, each one containing a single chromosome. Spores can eventually germinate to produce another hypha that grows by tip extension. Seemingly, both forms of cell division operate by an entirely different mechanism to that which operates in rod-shaped bacteria, although new evidence, produced by the applicant, suggests that streptomycetes may divide in a similar fashion to other bacterial after all. In order to investigate this, streptomycete cell division will be examined by videoing growth and chromosome population of the tips of growing hyphae. This will allow the exact order and location of key proteins and chromosomal regions during growth and sporulation of this organism to be identified. By comparison of the events and processes that take place during cell division of this unusual filamentous organism with those of rod-shaped microbes a better understanding of the practices that are shared between all bacterial will be obtained.

Committee	Closed Committee - Genes & Developmental Biology (GDB)
Research Topics	Microbiology
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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