, 2003; Avonce et al., 2006; Cardoso et al.,

2007). It is tempting to speculate that A. baumannii trehalose production contributes to the organism’s ability to tolerate desiccation and thus may contribute to its transmission in the hospital setting. RT-PCR confirmed that members of the trehalose metabolic pathway are dramatically upregulated during stationary as opposed to exponential phase growth (Fig. 2). A hallmark of biofilm assembly is the transition from surface attachment to biofilm accumulation and maintenance. In that regard, our data also indicated that genes that are known to be associated with the initial stages of biofilm formation are Cilomilast in vivo predominantly expressed during exponential growth, whereas genes associated with biofilm maintenance are upregulated during stationary phase. More specifically, during the initial stages of A. baumannii biofilm formation, the csu operon is thought to modulate pili formation and, consequently, contribute to pilus-mediated attachment to abiotic surfaces (Tomaras et al., 2003). We found Stem Cell Compound Library that two members of the csu operon, csuA/B (A1S_2218) and csuC (A1S_2215), as well as a putative pili assembly chaperone (A1S_1509), were upregulated during exponential phase of growth. Conversely, during stationary

phase of growth, putative members of the second messenger cyclic diguanylate (c-di-GMP; A1S-1949) and exopolysaccharide (A1S_1987) synthesis machinery were upregulated. In Pseudomonas aeruginosa, a close A. baumannii relative, c-di-GMP is hypothesized to play a role in the latter stages of biofilm formation. C-di-GMP augments biofilm maturation in two ways:

(1) it activates extracellular polysaccharide production, leading to a thickening of biofilm matrices, BCKDHA and (2) it suppresses twitching motility and swimming (Tamayo et al., 2007). Collectively, these results indicate that exponential and stationary phase-induced ORFs would allow A. baumannii to initiate attachment to a surface, produce exopolysaccharide, and then mature into a hardy biofilm. Gram-negative bacterial secretion systems are responsible for the translocation of proteins across the double membrane. During exponential phase, a putative general secretion pathway protein (A1S_0269), with homology to type II secretion system (T2SS) proteins, was upregulated. Additionally, five loci from the Sec pathway were also induced; this pathway is essential in transporting proteins across the inner membrane before they can be excreted by the T2SS. In several bacterial species, including Vibrio cholerae and P. aeruginosa, the T2SS secretes toxins, proteases, phospholipases, and other virulence-associated proteins (Sandkvist, 2001). A putative type III effector protein (A1S_0390) was also induced during exponential phase of growth.