Biofilm formation in Escherichia coli is affected by 3-(N-morpholino)propane sulfonate (MOPS)

An iTRAQ-Based Comparative Proteomics Analysis of the Biofilm and Planktonic States of Aeromonas veronii TH0426

Aeromonas veronii is a virulent fish pathogen that causes extensive economic losses in the aquaculture industry worldwide. In this study, a virulent strain of A. veronii TH0426 was used to establish an in vitro biofilm model. The results show that the biofilm-forming abilities of A. veronii TH0426 were similar in different media, peaking under conditions of 20 °C and pH 6. Further, isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics methods were used to compare the differential expression of A. veronii between the biofilm and planktonic cells. The results show alterations in 277 proteins, with 130 being upregulated and 147 downregulated. Pathway analysis and GO (Gene Ontology) annotations indicated that these proteins are mainly involved in metabolic pathways and the biosynthesis of secondary metabolites and antibiotics. These proteins are the main factors affecting the adaptability of A. veronii to its external environment. MRM (multiple reaction 27 monitoring) and qPCR (qPCR) were used to verify the differential proteins of the selected A. veronii. This is the first report on the biofilm and planktonic cells of A. veronii, thus contributing to studying the infection and pathogenesis of A. veronii.

Spent media from cultures of environmental isolates of Escherichia coli can suppress the deficiency of biofilm formation under anoxic conditions of laboratory E. coli strains

The prevailing lifestyle of bacteria is sessile and they attach to surfaces in structures known as biofilms. In Escherichia coli, as in many other bacteria, biofilms are formed at the air-liquid interface, suggesting that oxygen has a critical role in the biofilm formation process. It has been reported that anaerobically growing E. coli laboratory strains are unable to form biofilms even after 96 h of incubation on Luria Bertani (LB) medium. After analyzing 22,000 transposon-induced and 26,000 chemically-induced mutants we failed to isolate an E. coli laboratory strain with the ability to form biofilm under anaerobic growth conditions. Notably, seven strains from a collection of E. coli isolated from different hosts and the environment had the ability to form biofilm in the absence of oxygen. Interestingly, spent medium from cultures of one strain, Souza298, can promote biofilm formation of E. coli laboratory strains growing under anaerobic conditions. Our results led us to propose that laboratory E. coli strains do not release (or synthesize) a molecule needed for biofilm formation under anoxic conditions but that they bear all the required machinery needed for this process.

The lipopeptides mycosubtilin and surfactin enhance spreading of Bacillus subtilis strains by their surface-active properties

The colonizing behaviour and the pellicle formation of Bacillus subtilis strains producing different families of lipopeptides were evaluated under several cultural conditions. The pattern of lipopeptides produced determined the architecture of the colony on a swarming medium as well as the flotation and the thickness of the pellicle formed at the air/liquid interface. The overproduction of mycosubtilin, a lipopeptide of the iturin family, led to increased spreading but had no effect on pellicle formation. A physico-chemical approach was developed to gain an insight into the mode of action of the biosurfactants facilitating the colonization. A relationship between surface tension of the culture medium and spreading of a lipopeptide non-producing strain, B. subtilis 168, was established. Goniometry was used to highlight the modification of the in situ wettability in the area where spreading was enhanced. On a solid medium, co-cultures of a surfactin producing with other strains showed a diffusion ring of the surfactin around the colony. This ring characterized by a higher wettability favoured the propagation of other colonies.

Effect of oxygen and growth medium onin vitrobiofilm formation byEscherichia coli

The effects of oxygen availability onin vitrobiofilm formation by anEscherichia coliK-12 strain and 13 clinicalE. colistrains were compared. AllE. colistrains were capable of forming monospecies biofilm on polystyrene in aerobic media. The K-12 strain produced biofilm in both aerobic glucose minimal medium (ABTG), and aerobic trypticase soy broth (TSB) whereas the majority of the clinical strains produced significant biofilm only in aerobic TSB (9 of 13). In anaerobic media,E. coliK-12 and 9 of the 13 clinical strains were capable of forming biofilmin vitro. Only three clinical strains formed biofilm in anaerobic TSB whereas six clinical strains produced detectable biofilm in anaerobic ABTG. None of the strains tested were capable of forming biofilm in both anaerobic ABTG and anaerobic TSB. Strains that were good biofilm formers in aerobic ABTG also produced the highest amount of biofilm in anaerobic ABTG (R2= 0.90). Image analysis revealed notable differences in architecture for biofilms grown in the presence and in the absence of oxygen. In aerobic ABTG, the biofilm was dominated by tall, mushroom-shaped microcolonies with pores and channels whereas biofilm in anaerobic ABTG was thinner and less heterogeneous, resulting in reduced maximum thickness and biovolume. Analysis of phospholipid fatty acid (PLFA) profiles fromE. coliK-12 and three clinical strains did not reveal a specific pattern associated with the biofilm phenotypes. Interestingly, the clinicalE. colistrains adjusted their PLFA composition much more than didE. coliK-12 in response to changes in growth regimens. Collectively, the results indicate that oxygen availability may affectE. colibiofilm formation in minimal and complex media. The results confirm thatE. coliK-12 and some clinicalE. colistrains are capable of formingin vitrobiofilm under anaerobic conditions. However, the data also suggest that this attribute is highly strain dependent and may vary significantly among clinical isolates.

Anaerobic growth does not support biofilm formation in Escherichia coli K-12

Association with a surface in a structure known as biofilm is the prevailing microbial lifestyle. Here we show the kinetics of biofilm formation of Escherichia coli W3110 in static cultures growing under aerobic or anaerobic conditions. Aerobically growing cells in LB medium started to produce detectable amounts of biofilm after 4 to 8 h, displaying maximal accumulation of formed biofilm at 24 h, corresponding to the onset of stationary phase. Then an abrupt reduction in the biomass of the biofilm was observed. This decrease was not prevented by external addition of fresh nutrients and coincided with the depletion of oxygen as measured by the enzymatic activity of the AdhE protein. No biofilm formation was detected in cultures grown anaerobically in LB or LB supplemented with nitrate, nitrite, DMSO or fumarate, even after 72 h of incubation, well inside the stationary phase, suggesting that under anaerobic growth conditions E. coli cannot form biofilms.