1 mM). Compared with cells harboring the control vector, increased expression find more of YmdB inhibited biofilm formation by up to 80% in the presence or absence of IPTG (Figure 1A). The effect was linearly correlated
with IPTG concentration (10-6 to 10-1 mM), with no further reduction observed above 1 mM IPTG (data not shown). The physiological relevance of this inhibitory effect of YmdB is shown in Figure 1B. The total relative level of YmdB protein was assessed by Western Blotting  and was found to increase by 2.2- to 5.7-fold in the presence of increasing concentrations of IPTG (Figure 1B) (increased YmdB expression in the absence of IPTG results from the leaky lac promoter in the ASKA plasmids) . The changes in YmdB levels are similar to those observed in vivo following growth- or cold-stress (2- to 8-fold)
 and are thus physiologically relevant. Figure 1 YmdB inhibits biofilm formation. (A) Inhibition of biofilm formation by YmdB overexpression. E. coli cells containing either pCA24N (−gfp) or ASKA-ymdB (−) were grown at 37°C for 24 h in LB medium containing 0 to 10-1 mM IPTG. Biofilm formation was analyzed, and mean values calculated HTS assay (n = 10, p = 0.05). (B) Western blot analysis of YmdB expression levels. Total cellular proteins from the cells described in (A) were reacted with antibodies against YmdB or S1. Changes in YmdB protein levels from ASKA-ymdB induced by IPTG were determined relative to the levels of chromosomally-encoded YmdB protein derived from pCA24N (-gfp) vector-containing cells Isotretinoin (indicated below). RNase III does not affect biofilm inhibition by YmdB The YmdB protein regulates RNase
III activity through the formation through the proposed formation of an RNase III/YmdB heterocomplex ; hence, it was important to clarify whether the biofilm phenotype mediated by ectopic expression of YmdB is similar to that mediated by RNase III inhibition. Biofilm formation in the absence of RNase III (rnc14) increased by ~52% (Figure 2A), implying that inhibition of biofilm formation is independent of RNase III/YmdB heterocomplex, and that an alternative, hitherto uncharacterized, function of YmdB exists. To verify this possibility, we measured the inhibition of biofilm formation in the presence of YmdB overexpression (confirmed in Figure 2B) against an rnc + and rnc14 background. The results showed that inhibition was almost the same between the wild-type strain (~70%) and the strain lacking RNase III (~67%) (Figure 2A). By contrast, processing of pnp’-‘lacZ mRNA, a known target for YmdB-mediated inhibition of RNase III activity , is fully dependent on RNase III (Additional file 1: Figure S2). Taken together, these results indicate that YmdB overexpression inhibits biofilm formation via an RNase III-independent pathway.