Complementary approaches were employed to characterize transitional episodes in Pseudomonas aeruginosa biofilm development using direct observation and whole-cell protein analysis. Microscopy and in situ reporter gene analysis were used to directly observe changes in biofilm physiology and to act as signposts to standardize protein collection for two-dimensional electrophoretic analysis and protein identification in chemostat and continuous-culture biofilm-grown populations. Using these approaches, we characterized five stages of biofilm development: (i) reversible attachment, (ii) irreversible attachment, (iii) maturation-1, (iv) maturation-2, and (v) dispersion. Biofilm cells were shown to change regulation of motility, alginate production, and quorum sensing during the process of development. The average difference in detectable protein regulation between each of the five stages of development was 35% (approximately 525 proteins). When planktonic cells were compared with maturation-2 stage biofilm cells, more than 800 proteins were shown to have a sixfold or greater change in expression level (over 50% of the proteome). This difference was higher than when planktonic P. aeruginosa were compared with planktonic cultures of Pseudomonas putida. Las quorum sensing was shown to play no role in early biofilm development but was important in later stages. Biofilm cells in the dispersion stage were more similar to planktonic bacteria than to maturation-2 stage bacteria. These results demonstrate that P. aeruginosa displays multiple phenotypes during biofilm development and that knowledge of stage-specific physiology may be important in detecting and controlling biofilm growth.

Pseudomonas aeruginosa Displays Multiple Phenotypes during Development as a Biofilm

A 10-min method for preparation of highly electrocompetent Pseudomonas aeruginosa cells: Application for DNA fragment transfer between chromosomes and plasmid transformation

Bacteria become highly tolerant to antibiotics when nutrients are limited. The inactivity of antibiotic targets caused by starvation-induced growth arrest is thought to be a key mechanism producing tolerance. Here we show that the antibiotic tolerance of nutrient-limited and biofilm Pseudomonas aeruginosa is mediated by active responses to starvation, rather than by the passive effects of growth arrest. The protective mechanism is controlled by the starvation-signaling stringent response (SR), and our experiments link SR-mediated tolerance to reduced levels of oxidant stress in bacterial cells. Furthermore, inactivating this protective mechanism sensitized biofilms by several orders of magnitude to four different classes of antibiotics and markedly enhanced the efficacy of antibiotic treatment in experimental infections.

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Active Starvation Responses Mediate Antibiotic Tolerance in Biofilms and Nutrient-Limited Bacteria

Pseudomonas aeruginosa causes chronic biofilm infections, and its ability to attach to surfaces and other cells is important for biofilm formation and maintenance. Mutations in a gene called wspF, part of a putative chemosensory signal-transduction operon, have been shown to result in cell aggregation and altered colony morphology. The WspF phenotypes depend on the presence of WspR, which is a member of a family of signal transduction proteins known as response regulators. It is likely that the effect of the wspF mutation is to cause constitutive activation of WspR by phosphorylation. WspR contains a GGDEF domain known to catalyze formation of a cytoplasmic signaling molecule cyclic diguanylate (c-diGMP). We determined that purified WspR catalyzed the formation of c-diGMP in vitro and phosphorylation stimulated this activity. We observed increased cellular levels of c-diGMP and increased biofilm formation in a wspF mutant. Expression of a protein predicted to catalyze degradation of c-diGMP reversed the phenotypes of a wspF mutant and inhibited biofilm initiation by wild-type cells, indicating that the presence of c-diGMP is necessary for biofilm formation. A transcriptome analysis showed that expression levels of at least 560 genes were affected by a wspF deletion. The psl and pel operons, which are involved in exopolysaccharide production and biofilm formation, were expressed at high levels in a wspF mutant. Together, the data suggest that the wsp signal transduction pathway regulates biofilm formation through modulation of cyclic diguanylate levels.

https://www.pnas.org/content/pnas/102/40/14422.full.pdf

A chemosensory system that regulates biofilm formation through modulation of cyclic diguanylate levels.

Iron serves as a signal in Pseudomonas aeruginosa biofilm development We examined the influence of mutations in known and putative iron acquisition-signaling genes on biofilm morphology In iron-sufficient medium, mutants that cannot obtain iron through the high-affinity pyoverdine iron acquisition system form thin biofilms similar to those formed by the parent under low iron conditions If an iron source for a different iron acquisition system is provided to a pyoverdine mutant, normal biofilm development occurs This enabled us to identify iron uptake gene clusters that likely serve in transport of ferric citrate and ferrioxamine We suggest that the functional iron signal for P aeruginosa biofilm development is active transport of chelated iron or the level of internal iron If the signal is internal iron levels, then a factor likely to be involved in iron signaling is the cytoplasmic ferric uptake regulator protein, Fur, which controls expression of iron-responsive genes In support of a Fur involvement, we found that with low iron a Fur mutant was able to organize into more mature biofilms than was the parent The two known Fur-controlled small regulatory RNAs (PrrF1 and F2) do not appear to mediate iron control of biofilm development This information establishes a mechanistic basis for iron control of P aeruginosa biofilm formation

https://www.pnas.org/content/pnas/102/31/11076.full.pdf

Iron and Pseudomonas aeruginosa biofilm formation

A broad-host-range Flp-FRT recombination system for site-specific excision of chromosomally-located DNA sequences: application for isolation of unmarked Pseudomonas aeruginosa mutants.

A DNA fragment containing the Pseudomonas aeruginosa fabD (encoding malonyl-coenzyme A [CoA]:acyl carrier protein [ACP] transacylase), fabG (encoding beta-ketoacyl-ACP reductase), acpP (encoding ACP), and fabF (encoding beta-ketoacyl-ACP synthase II) genes was cloned and sequenced. This fab gene cluster is delimited by the plsX (encoding a poorly understood enzyme of phospholipid metabolism) and pabC (encoding 4-amino-4-deoxychorismate lyase) genes; the fabF and pabC genes seem to be translationally coupled. The fabH gene (encoding beta-ketoacyl-ACP synthase III), which in most gram-negative bacteria is located between plsX and fabD, is absent from this gene cluster. A chromosomal temperature-sensitive fabD mutant was obtained by site-directed mutagenesis that resulted in a W258Q change. A chromosomal fabF insertion mutant was generated, and the resulting mutant strain contained substantially reduced levels of cis-vaccenic acid. Multiple attempts aimed at disruption of the chromosomal fabG gene were unsuccessful. We purified FabD as a hexahistidine fusion protein (H6-FabD) and ACP in its native form via an ACP-intein-chitin binding domain fusion protein, using a novel expression and purification scheme that should be applicable to ACP from other bacteria. Matrix-assisted laser desorption-ionization spectroscopy, native polyacrylamide electrophoresis, and amino-terminal sequencing revealed that (i) most of the purified ACP was properly modified with its 4'-phosphopantetheine functional group, (ii) it was not acylated, and (iii) the amino-terminal methionine was removed. In an in vitro system, purified ACP functioned as acyl acceptor and H(6)-FabD exhibited malonyl-CoA:ACP transacylase activity.

Characterization of a pseudomonas aeruginosa fatty acid biosynthetic gene cluster : purification of acyl carrier protein (acp) and malonyl-coenzyme a :acp transacylase (fabd)

High-plex imaging of RNA and proteins at subcellular resolution in fixed tissue by spatial molecular imaging.


 As T-cells mature, genes encoding T-cell receptor (TCR) segments are somatically recombined to generate a diverse repertoire of receptors specific to unique antigens. The resultant TCR diversity, and subsequent clonal expansion events, are critical in understanding the adaptive immune response to pathogens and cancers. While many methods have been developed to determine specific clonotypes and overall TCR diversity present in various tissues, these methods to date have failed to capture spatial orientation and arrangement of T-cells engaging with their microenvironment. Tracking T-cell migration and infiltration into the tumor has thus been limited to post-hoc low-plex profiling methods. To better understand T-cell localization during tumor development, we have developed a TCR profiling panel for the GeoMx® Digital Spatial Profiler that can be combined with the GeoMx Cancer Transcriptome Atlas (CTA) or Human Whole Transcriptome Atlas (WTA). This novel spatial assay enables simultaneous quantification of all functional TCR constant, variable and joining segments in situ along with transcriptome-wide gene expression profiling in spatially defined regions of a tissue. We validated the performance of the TCR probe pool in inflamed tonsil and cell pellet arrays, demonstrating comparable sensitivity and specificity relative to orthogonal methods. We next used the GeoMx TCR spike-in panel to characterize intra- and inter-patient TCR heterogeneity in a cohort of 68 T-cell lymphomas to track clonal interactions between the malignant and non-malignant immune microenvironment. We demonstrate the ability to link the spatial context of TCR segment expression to activation of malignant signaling cascades as well as non-cancerous T-cell response to the presence of other immune cells and cancer-associated signaling. Together, the combination of our TCR spike-in panel with the CTA or WTA illuminates spatial distribution of T-cell clones paving the way for studies to comprehensively link TCR clonality changes to the tumor microenvironment.
 FOR RESEARCH USE ONLY. Not for use in diagnostic procedures.
 Citation Format: Michelle A. Kriner, Katrina van Raay, Jason W. Reeves, Kit A. Fuhrman, Andrew Klock, Alecksandr Kutchma, Erin Piazza, Joseph Beechem. Spatially resolved T-cell receptor profiling elucidates relationships between TCR diversity, immune infiltration, and cancer-associated pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1364.

Abstract 1364: Spatially resolved T-cell receptor profiling elucidates relationships between TCR diversity, immune infiltration, and cancer-associated pathways

Alecksandr J. Kutchma

Papers

A broad-host-range Flp-FRT recombination system for site-specific excision of chromosomally-located DNA sequences: application for isolation of unmarked Pseudomonas aeruginosa mutants.

Characterization of a pseudomonas aeruginosa fatty acid biosynthetic gene cluster : purification of acyl carrier protein (acp) and malonyl-coenzyme a :acp transacylase (fabd)

High-plex imaging of RNA and proteins at subcellular resolution in fixed tissue by spatial molecular imaging.

Abstract 1364: Spatially resolved T-cell receptor profiling elucidates relationships between TCR diversity, immune infiltration, and cancer-associated pathways