Bacteriolytic activities of the free-living soil amoebae,Acanthamoeba castellanii, Acanthamoeba polyphaga andHartmannella vermiformis

Abstract

Bacteriolytic activities of axenically grown free-living soil amoebae Acanthamoeba castellanii, Acanthamoeba polyphaga and Hartmannella vermiformis towards various Gram-positive and Gram-negative bacteria were determined. A spectrophotometric assay revealed that the specific bacteriolytic activities of both Acanthamoeba species were higher as those of the three Hartmannella strains. Bacillus megaterium, Bacillus subtilis, Chromatium vinosum, Micrococcus luteus and Pseudomonas fluorescens were more easily lysed than the other bacteria tested. Agrobacterium tumefaciens, Klebsiella aerogenes and Serratia marcescens were hardly affected at all by the amoebal bacteriolytic activities. Among the Gram-negative bacteria we observed differences in lysis sensitivity while the Gram-positive bacteria tested were sensitive to lysis. Isoelectric focusing (IEF) gel-electrophoresis in the pH range 3-10 was performed to separate the bacteriolytic isoenzymes of amoebae. Bacteriolytic patterns were shown by using an activity assay in which lysis bands were formed in the agar/bacteria gel-overlay. The activity assay revealed remarkable differences in typical banding patterns for bacteriolytic activities among amoebae. Distinct differences between typical pI points of bacteriolytic activities in Acanthamoeba and Hartmannella were shown. Bacteriolytic activities of Hartmannella were more pronounced and observed in the isoelectric points (pI) range of 4.0-9.3 while for Acanthamoeba the range was pI 4.5-8.9.

Enhanced survival but not amplification of Francisella spp. in the presence of free-living amoebae

“…With various Gram-positive and Gram-negative bacteria that are commonly found in soil and water as the sole food source, Ap, Ac, and Vv cells exhibited an increased growth and ammonium production rate, in that order, indicating select Ap and Ac strains are more adept at utilizing bacteria as a food source than Vv [37]. However, the ability to degrade microbial cell wall components, or bacteriolytic activity, of Vv culture lysates were greater than Ac and Ap cultures when evaluating lysis of similar environmental Gram-negative and Gram-positive bacteria [38], indicating that the feeding behavior assessment of FLA may be assay and strain dependent. Pathogenic isolates of Acanthamoeba spp., Ac, Ap, Acanthamoeba palestinensis, Acanthamoeba astronyxis, and Acanthamoeba griffini can produce cytopathic effects on corneal epithelial cells and can tolerate high osmolarity growth media compared to their non-pathogenic counterparts [39].…”

Microorganisms Resistant to Free-Living Amoebae

“…Thus, E. coli, E. aerogenes, and S. maltophilia appear to be better nutrient sources for amoebae than are Staphylococcus epidermidis, Serratia marcescens, and Pseudomonas spp. (243,244). This explains why Enterobacter spp., Klebsiella spp., and E. coli are preferred for amoebal enrichment procedures (193,217).…”

“…(244), explaining why these species are generally preferred to Pseudomonas spp. for axenic cultures of Acanthamoeba and Naegleria spp.…”

“…More importantly P. aeruginosa was shown to inhibit the growth of Acanthamoeba castellanii, especially in PYG and/or in the presence of an high bacterium-toamoeba ratio (243). The presence of toxic pigments possibly explains these observations (243,244). Qureshi et al hypothethized that these pigments or amoebicidal enzymes produced by P. aeruginosa might explain the exclusive recovery of either Pseudomonas or Acanthamoeba from patients with keratitis (198).…”

Microbial-faunal interactions in the rhizosphere and effects on plant growth

“…The stimulation of plant growth in the presence of protozoa may be due to indirect effects since protozoan grazing on the rhizosphere microflora results in significant changes in the composition of the microbial community [130] and associated soil biological processes [103,125]. Protozoa and nematodes are known to feed selectively on certain species of bacteria [17,53,118,123] and it has been demonstrated for flagellates, amoebae and ciliates, that they specifically stimulate nitrifying bacteria [2,52,124] indicating that protozoan grazing facilitates the establishment of certain bacterial species.…”