Effect of relA and spoT deletions on Escherichia coli biofilm formation




Balzer, Grant J.

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Bacteria predominantly grow as surface adherent biofilm communities composed of high cell density aggregates (microcolonies). Within microcolonies, gradients of nutrients and growth rates exist from the outer to inner cells due to diffusion and nutrient uptake. Therefore, in order to grow as a biofilm, cells must possess the capacity to survive under conditions of nutrient depletion. The stringent response is one starvation-survival mechanism that regulates gene expression at the level of RNA transcription. Two major genes whose products control the stringent response in Escherichia coli are relA and spoT. To understand the relationship between the stringent response and biofilm formation, two E.coli K-12 derivatives, DS 291 and its isogenic relA spoT derivative, DS 293, were grown as biofilms using a chemostat coupled to a modified Robbins device (MRD) containing plugs of silicone rubber catheter material. The strains were grown at two dilution rates (0.025 h-1 and 0.25 h-1) in a MOPS minimal medium with serine-limitation. At the low dilution rate, a significant decrease (P < 0.05) was noted with the relA spoT strain only. When evaluating biofilm density as an adherence ratio, significant differences were noted at both dilution rates. Examination of biofilms by scanning confocal laser microscopy illustrated qualitative differences in biofilm structure in the wild type and relA spoT strains. This study indicates that the stringent response is important for E.coli biofilm growth.



Escherichia coli, biofilms, relA spoT


Balzer, G. J. (2000). Effect of relA and spoT deletions on Escherichia coli biofilm formation (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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