Streptococcus uberis transposon mutant screen reveals a negative role for LiaR homologue in biofilm formation

AIMS: The environmental pathogen Streptococcus uberis causes intramammary infections in dairy cows. Because biofilm growth might contribute to Strep. uberis mastitis, we conducted a biological screen to identify genes potentially involved in the regulation of biofilm growth. METHODS AND RESULTS: By screening a transposon mutant library of Strep. uberis, we determined that the disruption of 13 genes (including hasA, coaC, clpP, miaA, nox and uidA) led to increased biofilm formation. One of the genes (SUB1382) encoded a homologue of the LiaR response regulator (RR) of the Bacillus subtilis two‐component signalling system (TCS). Electrophoretic mobility shift assays revealed that DNA binding by LiaR was greatly enhanced by phosphorylation. Two‐dimensional differential in‐gel electrophoresis analyses of the liaR mutant and the parental Strep. uberis strain revealed five differentially produced proteins with at least a 1·5‐fold change in relative abundance (P