Co-regulation of β-lactam resistance, alginate production and quorum sensing in Pseudomonas aeruginosa

The legend and labels for Fig. 1 on page 151 are incorrect. The last line of the legend should read one milliunit (mU) of β-lactamase is defined as 1 nmol nitrocefin hydrolysed min⁻¹ (µg protein)⁻¹, not one Miller unit of β-lactamase is defined as 1 nmol nitrocefin hydrolysed min⁻¹ (µg protein)⁻¹. The y-axis of Fig. 1 should be labelled β-lactamase activity (mU), not β-lactamase activity (Miller units).

Fig. 1.

β-Lactamase expression in the Alg⁺ PDOampR mutant. Assays were performed using the parent strain Alg⁺ PDO300, the mutant Alg⁺ PDOampR and Alg⁺ PDOampR (pAmpR) in the absence (−) and presence (+) of an inducer. The plasmid pAmpR carries the wild-type ampR gene on a broad-host-range low-copy-number plasmid pME6030 (Heeb et al., 2000). Fresh cultures of OD₆₀₀ 0.6–0.8 were induced with 100 µg benzylpenicillin ml⁻¹ for 3 h before harvesting. Assays were performed on sonicated lysate using nitrocefin as a chromogenic substrate. Assays were performed in triplicate. One milliunit (mU) of β-lactamase is defined as 1 nmol nitrocefin hydrolysed min⁻¹ (µg protein)⁻¹.

The labels for Fig. 2 on page 151 are incorrect. The y-axis of Fig. 2 should be labelled β-galactosidase activity (Miller units), not β-lactamase activity (Miller units).

Fig. 2.

The effects of the ampR mutation on algT/U transcription. The promoter fusion P_algT/U-lacZ was introduced into Alg⁻ PAO1, Alg⁻ PAOampR, Alg⁺ PDO300 and Alg⁺ PDOampR. Induction was carried out using 500 µg benzylpenicillin ml⁻¹ and the β-galactosidase activity was determined in Miller units after 30 min incubation. The basal level of expression was detected in the promoterless lacZ vector, pLP170.

The labels for Fig. 3 on page 152 are incorrect. The y-axis of Fig. 3 should be labelled β-galactosidase activity (Miller units), not β-lactamase activity (Miller units). The correct figures are reproduced below.

Fig. 3.

The effects of the ampR mutation on QS las and rhl gene transcription. The alteration in the transcription of the QS systems in Alg⁻ PAO1 (hatched bars), Alg⁻ PAOampR (grey bars), Alg⁺ PDO300 (white bars) and Alg⁺ PDOampR (black bars) was monitored using four transcriptional fusions, P_lasI-lacZ, P_lasR-lacZ, P_rhlI-lacZ and P_rhlR-lacZ. The promoterless lacZ vector has a low basal level of activity of <20 Miller units.