Assessing the involvement of BslA in plant-root associated biofilms

Abstract

Many pathogens are capable of causing plant diseases that can decimate yields of important food crops. The increasing demand for food production, driven by an ever growing human population, has made the prevention of plant diseases an extremely important and pressing issue. Current methods for promoting plant growth and preventing plant diseases include various petrochemical derived fertilisers and pesticides. In addition to the harmful effects many of these chemicals can have on the environment and human health, pathogens are increasingly developing resistances to these methods. As such there is an urgent requirement to find effective alternatives to current disease control methods. One such promising alternative is the practice of biological control, the process by which microorganisms are used to prevent plant diseases. The formation of biofilms on plant roots is often vital for biocontrol. Biofilms are complex multicellular communities of bacteria interacting with each other, and encased in a self-produced extracellular matrix. The matrix is composed of exopolysaccharides, proteins and nucleic acids, and provides protection to the cells from various stresses. One microorganism that relies on biofilm formation for biocontrol, is the Gram-positive soil-dwelling bacterium Bacillus subtilis. B. subtilis biofilm formation is regulated by signalling networks that result in the production of two essential matrix components; an exopolysaccharide (EPS) and a fibrous protein (TasA), in addition to a bacterial hydrophobin (BslA). TasA and EPS have previously been shown to be required for biofilm formation and biocontrol by B. subtilis on many different plant species. However, no previous work has investigated a possible role for BslA in plant-associated biofilm formation. The work presented in this thesis aimed to assess the role of BslA in the plant-associated life style of B. subtilis. The first part of this study looked to investigate the potential involvement of BslA in plant-associated biofilm formation. Results from this section indicated that BslA is not required for initial plant root colonisation or the early stages of biofilm formation on plant roots, but that it may be required for persistence of the biofilm on the root over longer time periods. The second part of this study aimed to examine the potential role of BslA in biocontrol by a commercially available B. subtilis biocontrol strain. Before any role for BslA could be elucidated in this system, a bslA mutation must first be introduced into the chosen B. subtilis strain. Attempts to introduce a bslA mutation into commercial biocontrol isolates led to the surprising identification of reportedly B. subtilis commercial biocontrol strains as B. amyloliquefaciens strains, raising speculation as to whether there are any truly B. subtilis commercial biocontrol strains. Together these results hint at some role for BslA in the plant-associated system but more work is required to clearly elucidate the involvement of BslA in this environment.

Date of Award	2016
Original language	English
Awarding Institution	University of Dundee
Supervisor	Nicola Stanley-Wall (Supervisor)