The transcriptomes of logarithmic-and stationary-phase Pseudomonas aeruginosa planktonic cultures and static biofilms of different stages of development were compared. Developing and confluent biofilm transcriptomes were found to be related to those of logarithmic-and stationary-phase planktonic cultures, respectively. In addition, a number of novel genes were up-regulated in developing and confluent biofilms, including genes encoding putative solute transport proteins and transcriptional regulators, respectively.Pseudomonas aeruginosa is a versatile organism that can survive in soil, marshes, and marine habitats, on plant and animal tissue, and on nonliving surfaces (24). At 6.3 million base pairs (5,570 open reading frames [ORFs]), the genome of P. aeruginosa is one of the largest bacterial genomes that have been sequenced (24), and its size and complexity are thought to enable survival in diverse environments. Central to this survival is the ability to adopt and switch between free-living (planktonic) and biofilm (surface-attached) lifestyles. Biofilms are populations of microorganisms adhered to a surface or interface, and P. aeruginosa biofilms arise in a variety of clinical settings, including the cystic fibrosis lung, urinary catheters, and contact lenses (22,23,29). Biofilm infections are notoriously difficult to eradicate, even after prolonged antimicrobial therapy, and it is well documented that biofilms are less susceptible to antimicrobial agents than free-living (planktonic) bacteria and provide protection from the host immune response (5, 9, 11).Control of gene expression in P. aeruginosa is the key determinant of its flexibility, and a variety of highly integrated regulatory mechanisms have been described previously. These include the LasR-LasI and RhlR-RhlI cell density-dependent quorum-sensing (QS) systems and a large number of twocomponent regulatory systems (6,13,16,24,27). Knowledge of the specific genes required by P. aeruginosa for survival under different environmental conditions will improve our understanding of the biology of this organism and form the basis for the rational design of novel therapeutic approaches. The recent development of an Affymetrix GeneChip microarray representing 5,549 ORFs on the P. aeruginosa chromosome now enables the analysis of global gene expression of this organism under defined growth conditions and the comparison of different growth states. Here we provide the first study in which the transcriptional profiles of two bacterial planktonic phases (logarithmic phase [LP] and stationary phase [SP]) and multiple biofilm time points (8,14,24, and 48 h) are compared.Biofilm characterization. Previous studies using continuous culture biofilm systems (10, 17) have shown that biofilms form in a sequential process: (i) attachment, (ii) microcolony formation, and (iii) biofilm maturation. Using a Zeiss LSM510 confocal laser scanning microscope (40ϫ magnification), we characterized biofilm development of wild-type P. aeruginosa strain PAO1 (7) tagged with green fluores...

SummaryThe molecular genetic basis of high-frequency serotype 3 capsule phase variation in Streptococcus pneumoniae (the pneumococcus) was investigated. Pneumococci were grown in sorbarod biofilms at 348C to mimic nasopharyngeal carriage. Different type 3 pneumococci commonly associated with invasive disease generated apparently random tandem duplications of 11-239 bp segments within the cap3A gene of the type 3 capsule locus. These duplications alone were found to be responsible for high-frequency capsule phase variation, in which (phase off) acapsular variants possessed duplications within cap3A, and (phase on) capsular revertants possessed wildtype cap3A genes, indicating the precise excision of the duplication. Additionally, the frequency of phase reversion (off to on) was found to exhibit a linear relationship between (log) frequency of reversion and (log) length of duplication. This apparently random duplication giving rise to phase variation is in stark contrast to the 'preprogrammed' contingency genes in many Gram-negative organisms that possess homopolymeric sequence repeats or motifs for sitespecific recombination.

Background: Pseudomonas aeruginosa is a genetically complex bacterium which can adopt and switch between a free-living or biofilm lifestyle, a versatility that enables it to thrive in many different environments and contributes to its success as a human pathogen.

Transcriptomic and phenotypic studies showed that pyocins are produced in Pseudomonas aeruginosa PAO1 aerobic and anaerobic biofilms. Pyocin activity was found to be high in slow-growing anaerobic biofilms but transient in aerobic biofilms. Biofilm coculture of strain PAO1 and a pyocin-sensitive isolate showed that pyocin production had a significant impact on bacterial population dynamics, particularly under anaerobic conditions.