Schematic description of quantifying the biofilm formation capability of single mutants of essential genes for <i>P. aeruginosa</i>.

<p>The genes positively associated with <i>P. aeruginosa</i> biofilm formation are used to determine biofilm-associated reactions in Step 1. The essential gene <i>m</i> (e.g., PA1756 gene) is used as a reference gene in Steps 2 through 3 to illustrate the proposed approach for quantifying the potential of a single mutant to form biofilms. Specifically, reactions associated with gene <i>m</i> are partially mutated, and the flux distributions of all biofilm-associated reactions for both wide-type and mutant strains are quantified in Step 2. The relative change of activity through all biofilm-associated reactions for the gene <i>m</i> mutant is quantified in Step 3. A large enhancement in the activity of biofilm-associated reactions implies a large potential for the single mutant to form biofilms. The profiles for four mutants are given as examples in Step 3. Mutant 4 exhibits the lowest potential to form biofilms. The relative activity change profiles for all single mutants are used to categorize essential genes into different clusters in Step 4. Mutant 4 is assigned to a different cluster from that for the other three mutants, as its relative activity profile is not similar to those for the other mutants in both the shape and the magnitude. The essential planktonic-growth genes whose mutants might not induce biofilm formations are identified from the cluster results and regarded as potential target genes. For example, gene PA1756, which corresponds to mutant 4 in Step 3, is one potential gene target due to the low enhanced activities through those biofilm-associated reactions in its mutant. The biofilm-associated reactions whose activity levels are apparently enhanced in most mutants are identified in Step 5. These reactions indicate the underlying mechanisms for <i>P. aeruginosa</i> biofilm formation.