Initial Phases of Starvation and Activity of Bacteria at Surfaces

Abstract

The activity of the hydrophilic Vibrio sp. strain DW1 and the hydrophobic Pseudomonas sp. strain S9, which both undergo starvation-induced responses, was examined at nutrient-enriched and nutrient-deficient interfaces. The initial period of response to a starvation regime ("dwarfing" phase) is a sequence of two processes: fragmentation and continuous size reduction of the fragmented cells. This dwarfing phase is also one of intense metabolic activity as supported by 02 uptake measurements of the endogenous metabolism and the use of inhibitors of the proton flow, the electron transport chain, and membrane-bound ATPase. Hydrophilic bacteria become even smaller at nutrient-deficient surfaces than in the liquid phase upon starvation, and this is reflected in a higher endogenous metabolism exhibited by surface-associated cells compared with those in the liquid phase. On the other hand, hydrophobic bacteria dwarfing at surfaces did not exhibit a greater size reduction and exhibited an endogenous metabolism that was only slightly higher than that of cells in the liquid phase. Bacterial scavenging of surface-localized nutrients is related to the degree of irreversible binding of dwarf and starved bacteria, which in turn may be related to the degree of cell surface hydrophobicity.

The role of motility in the in vitro attachment of Pseudomonas putida PaW8 to wheat roots

“…This contrasted with the results from non-competitive attachment studies in phosphate bu¡er. Here, overall, the motile cells attached in signi¢cantly greater numbers than non-motile cells at each time point when present at 10 6 and 10 7 cfu ml 31 in the attachment solution, but not at 10 8 cfu ml 31 in the attachment solution ( Fig. 1D^F).…”

“…Pseudomonas strains were inoculated on to the surface of NA (containing antibiotics where appropriate at 50 Wg ml 31 ) and incubated at 30³C for 18 h. Cells were resuspended in attachment solution (0.01 M phosphate bu¡er containing 2.25 g l 31 NaCl, pH 7.0, or LB) and the optical density of the suspension adjusted to 0.23 at OD 600 nm (equivalent to 3U10 8 cfu ml 31 ). Optical density was measured in 1-cm path-length cuvettes using a Philips 8720 UV/VIS scanning spectrophotometer (Philips, UK).…”

“…Individual root pieces were placed in 1 ml LB containing 1 Wl of n-decylaldehyde in a cuvette, vortexed for 10 s, and RLU measured immediately in the luminometer. RLU ml 31 and cfu ml 31 of attachment solution were also measured at each sample point in order to determine the RLU cell 31 . An average value for the motile or nonmotile strain could not be used as the RLU cell 31 varied between sample points during the 2 h experiment.…”

“…In non-competitive studies, motile and non-motile cells were present as single strains in LB or phosphate bu¡er at densities of 10 6 , 10 7 and 10 8 cfu ml 31 . In competitive studies, motile and non-motile strains were mixed in equal numbers in phosphate bu¡er.…”

“…Using such mutants we would be able to test the e¡ect of £agella, rather than motility per se on attachment. Using insertional inactivation by homologous recombination a series of non-motile strains were Table 1 Number of motile and non-motile cells attached to sterile wheat roots after 120 min incubation in LB and phosphate bu¡er at three inoculation densities cfu root 31 obtained (mot 3 £a 3 ), and one mutant retained its £agella (mot 3 £g ) but was defective in motility. The £agella that were observed by TEM attached to these cells appeared to be longer than normal, however the reason for the lack of motility of this strain was not determined.…”