Table 1.

Cues, signals and agents linked to the different modes of escapes from the biofilm. PDE, phosphodiesterase; DGC, diguanylate cyclase; batch-grown biofilms, biofilms grown in microtiter plates, petri dishes or other containers without medium being replaced over the course of biofilm growth; CV staining, biofilm biomass was stained with crystal violet; CFU, viability count based on colony forming units; SNP, sodium nitroprusside.

Cue, Signal, factors	Species	Biofilm growth method/ Biofilm age and treatment	Effector Regulatory System	Source
Conditions linked to induction of biofilm dispersion
Oxygen depletion	Pseudomonas aeruginosa	Semi-batch growth system using polystyrene surface; 2d biofilms; detection of biomass reduction by CV staining	PDE RbdA	[59]
Oxygen depletion, cessation of flow	Shewanella oneidensis	Flow cell 16 hr biofilms; dispersion noted by microscopy within 5 min post cessation of flow	Transcriptional regulators ArcA and CRP	[42,74]
Hydrogen peroxide	a. actinomycetemco mitans	6 hr microtiter dish biofilms or 4 -hr colony biofilms, and murine abscess infection model	Up-regulation of dspB expression encoding Dispersin B	[70]
Starvation, cessation of flow	P. putida	Flow cell 4d biofilms; detachment observed 15 min post flow cessation		[53]
Starvation, cessation of flow	P. aeruginosa P. fluorescens	Drip flow or capillary flow biofilm reactors; 4 d biofilms; dispersion assessed 3 d post flow cessation by spectroscopy		[75-78]
Sudden step-increase of carbon source concentration (glucose, glutamate, succinate, citrate)	P. aeruginosa	Continuous flow reactors (tube reactors, flow cells); 4-5 d biofilms; monitoring biofilm by CFU and microscopy for up to 60 min, with release of cells from the surface observable within 10 min Acute and chronic murine virulence model, using dispersion-deficient mutants	• Phosphorylation-dependent signaling (response inhibited with phosphatase inhibitor) • Increased cellular PDE activity • Decreased cellular c-di-GMP levels • Chemotaxis transducer BdlA • Heme-associated BdlA may be involved in redox/energy state sensing; BdlA cleavage and activation modulated by c-di-GMP • PDE DipA • DGC GcbA • Sensory protein NicD, DGC activity • Sensory protein NbdA, PDE activity • Release of matrix degrading enzymes • Virulence gene expression • Dispersion phenotype • Transcriptomic analysis	[27,38,39,44,49-52,79]
Sudden step-increase of carbon source concentration	Acinetobacter sp	Continuous-flow slide culture; dispersion response monitored by microcopy		[80]
Sudden step-increase of carbon source concentration	S. pneumoniae	72 hr biofilms grown on human respiratory epithelial cells (HRECs); 2 hr treatment		[54]
Ammonium chloride	P. aeruginosa	Continuous flow reactors (tube reactors, flow cells); 4-5 d biofilms; monitoring biofilm by CFU, microscopy, and biofilm effluent measurements for up to 60 min, with release of cells from the surface observable within 10 min	• Phosphorylation-dependent signaling (response inhibited with phosphatase inhibitor) • Chemotaxis transducer BdlA • PDE DipA	[44,51,52]
Heavy metals (mercury chloride, sodium arsenate), silver nitrate	P. aeruginosa	Continuous flow reactors (tube reactors, flow cells); 4-5 d biofilms; monitoring biofilm by CFU, microscopy, and biofilm effluent measurements for up to 60 min, with release of cells from the surface observable within 10 min	• Chemotaxis transducer BdlA • PDE DipA • DGC GcbA	[50-52]
Nitric oxide (via SNP)	P. aeruginosa	Batch-grown 24 hr biofilms attached to slides in petri dishes; biofilms exposed to NO for 24 hr; SYTO staining and microscopy	• Increased cellular PDE activity • Decreased cellular c-di-GMP levels • Chemotaxis transducer BdlA • Transcriptomic analysis	[40]
Nitric oxide (via SNP)	P. aeruginosa	Continuous flow reactors; 6 d biofilms; dispersion assessed via effluent measurement and microscopy under flowing conditions	• Sensory protein NbdA, PDE activity • MucR, dual activity (PDE, DGC) • Chemotaxis transducer BdlA • Release of matrix degrading enzymes • Virulence gene expression • Dispersion phenotype	[27,39]
Nitric oxide (via SNP)	Nitrosomonas europaea Ammonia oxidizer	Batch-grown 24 hr biofilms attached to wells of microtiter plate; biofilms treated for additional 24 hr; biomass detected by CV staining		[81]
Cis-2 decenoic acid (fatty acid signaling molecule)	P. aeruginosa E. coli K. pneumonia B.subtilis P. mirabilis S. aureus S. pyogenes C.albicans	Continuous flow reactors and microtiter plate biofilms; 4-7 d biofilms; endogenous and exogenous addition of cis-2 decenoic acid; direct microscopic evaluation of dispersion response under flowing conditions and microtiter plate dispersion assays	Fatty acid synthase DspI	[32]
Iron	P. aeruginosa	Batch-grown 48 hr biofilms in microtiter plate; co-treatment for 48 hrs; biomass evaluation by CV staining Continuous flow reactors (tube reactors, flow cells); 4-5 d biofilms; monitoring biofilm by microscopy and biofilm effluent measurements for up to 60 min, with release of cells from the surface observable within 10 min		[37,82]
Bile salt taurocholate	Vibrio cholerae	Prevents 24 hr biofilm formation in glass tubes when present in growth medium; Causes cell detachment from 24 hr glass tube biofilms within 1-2 hr; CV staining and microscopy		[55]
Factors linked to biofilm detachment (Enzymatic degradation of matrix components)
Cellulase	P. putida	2-3 d biofilms;1hr treatment	Cellulose-like matrix component	[41]
Proteinase K	P. putida	Batch-grown 2-3 d pellicle biofilms;1hr treatment	Proteolysis of adhesin LapA	[41]
Proteinase K	S. lugdunensis S. aureus Listeria monocytogenes	Batch-grown 24-72 hr biofilms in microtiter plates or petri dish systems; 2-6 hr treatment	Biofilm-associated protein Bap	[19,83,84]
Periodate	P. putida	Batch-grown 2-3 d pellicle biofilms; 1hr treatment	Cellulose-like matrix component	[41]
Periodate	S. epidermidis	Batch-grown 24 hr biofilms in microtiter plates or petri dish systems; 2 hr treatment	Cellulose-like matrix component	[19]
Dispersin B	A. actinomycetemco mitans A. pleuropneumoniae S. epidermidis	Batch grown 24 hr biofilms attached to polystyrene; 2hr treatment Batch grown 18-24 hr biofilms in microtiter plate; 2hr treatment	linear polymers of N-acetyl-D-glucosamines, matrix component	[17-19]
DNase	L. monocytogenes	72-hr polystyrene peg biofilms; 24 hr treatment		[84]
Alginate lyase	P. aeruginosa	Biofilms grown in petri dish system		[85]
Biosurfactant (viscosin)	P. fluorescens	1-d flow cell-grown biofilms; 7.5-17.5-hr microtiter biofilms; 9.5 hr treatment		[16]
Biosurfactant (rhamnolipids)	S. epidermidis	18-hr flow cell biofilms; 1 hr treatment		[16]
Conditions linked to desorption
Proteinase K	P. putida	Batch-grown 2-3 d pellicle biofilms; 1hr treatment	Adhesion LapA	[41]
Nitric oxide (via SNP)	Serratia marcescens V. cholerae E. coli Bacillus licheniformis S. epidermidis Fusobacterium nucleatum Candida albicans	Cell grown anaerobically in Schaedler Broth to an OD600 of 0.1; SNP added and cells allowed to attach for 4 h on a sterile glass slide; Slides washed and stained with CV; Microscopy for number of cells		[86]
Cis-2 decenoic acid (fatty acid signaling molecule)	P. aeruginosa	Continuous flow reactors; Microscopy under flowing conditions		[32]
Conditions linked to dispersion or biofilm architectural collapse
Reduction of c-di-GMP	P. aeruginosa	Overexpression of rcsB impairs formation of biofilms grown in microfermentors for 4 days. Cells attached to 24 well plates after 6 hr, induction of rscB, and dispersion (reduction in CV biomass) apparent within 45 min, with experiment taken out to 18 hr for complete biofilm removal	• Response regulator RcsB • Induction of PDE PvrR	[67]
Reduction of c-di-GMP	P. aeruginosa	4d drip flow or capillary flow biofilm reactors; dispersion assessed 3d post flow cessation		[77]
Reduction of c-di-GMP	P. putida	Batch-grown 10-24 hr biofilms, in microtiter plates; biofilm biomass evaluation by CV staining	• PDE YhjH • Adhesion LapA • Protease LapG	[41]
Cell-to-cell signaling molecules, mechanism of escape unclear
Quorum sensing: Acylated homoserine lactones (AHLs)	Yersinia pseudotuberculosis Rhodobacter sphaeroides	Aggregation in batch culture	Mutant of LuxR homolog YpsR are hyperaggreagative Inactivation of cerI, encoding a 7,8-cis-N-(tetradecenoyl)homoserine lactone synthase, results in mucoid colony phenotype and hyperaggregation in liquid	[87] [88]
Quorum sensing, Agr	S. aureus	Flow cells; 2-day old biofilms; loss of biofilm biomass monitored 1-2 d post glucose depletion	No biofilm biomass loss noted in agr mutant post 2 days of glucose depletion	[89]
DSF	Xanthamonas campestris	Aggregates in batch medium after overnight growth of rpfF mutants; Enzyme causes disaggregation within 30 min; DSF can prevent aggregate formation or cause complete disaggregation within 3 hr Aggregates in batch medium after overnight growth; DSF causes disaggregation within 3 hr	DSF and Rpf genes positively control synthesis of manA-encoded endo-β-1,4-mannanase which degrades the matrix	[35]
AI-2	V. vulnificus	12 hr biofilms in microtiter plates; CV staining to quantify attached cells; CFU counts to quantify detached cells	Host cells increase smcR (LuxR homolog) expression; SmcR downregulates genes associated with biofilm formation and up-regulates those associated with detachment including vvpE encoding an elastolytic protease	[71]