Impact of protozoan grazing on bacterial community structure in soil microcosms

R. Ronn, A. E. McCaig, James Ivor Prosser, B. S. Griffiths

Research output: Contribution to journalArticle

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Abstract

The influence of grazing by a mixed assemblage of soil protozoa (seven flagellates and one amoeba) on bacterial community structure was studied in soil microcosms amended with a particulate resource (sterile wheat roots) or a soluble resource (a solution of various organic compounds). Sterilized soil was reinoculated with mixed soil bacteria (obtained by filtering and dilution) or with bacteria and protozoa. Denaturing gradient gel electrophoresis (DGGE) of PCR amplifications of 16S rRNA gene fragments, as well as community level physiological profiling (Biolog plates), suggested that the mixed protozoan community had significant effects on the bacterial community structure. Excising and sequencing of bands from the DGGE gels indicated that high-G+C gram-positive bacteria closely related to Arthrobacter spp. were favored by grazing, whereas the excised bands that decreased in intensity were related to gram-negative bacteria. The percentages of intensity found in bands related to high G+C gram positives increased from 4.5 and 12.6% in the ungrazed microcosms amended with roots and nutrient solution, respectively, to 19.3 and 32.9% in the grazed microcosms. Protozoa reduced the average bacterial cell size in microcosms amended with nutrient solution but not in the treatment amended with roots. Hence, size-selective feeding may explain some but not all of the changes in bacterial community structure. Five different protozoan isolates (Acanthamoeba sp., two species of Cercomonas, Thaumatomonas sp., and Spumella sp.) had different effects on the bacterial communities. This suggests that the composition of protozoan communities is important for the effect of protozoan grazing on bacterial communities.

Original languageEnglish
Pages (from-to)6094-6105
Number of pages11
JournalApplied and Environmental Microbiology
Volume68
Issue number12
DOIs
Publication statusPublished - 2002

Keywords

  • 16S RIBOSOMAL-RNA
  • FRESH-WATER
  • NAKED AMEBAS
  • RELATIVE ABUNDANCE
  • BARLEY ROOTS
  • POPULATIONS
  • SIZE
  • DIGESTION
  • RATES
  • PCR

Cite this

Impact of protozoan grazing on bacterial community structure in soil microcosms. / Ronn, R.; McCaig, A. E.; Prosser, James Ivor; Griffiths, B. S.

In: Applied and Environmental Microbiology, Vol. 68, No. 12, 2002, p. 6094-6105.

Research output: Contribution to journalArticle

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AU - Griffiths, B. S.

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AB - The influence of grazing by a mixed assemblage of soil protozoa (seven flagellates and one amoeba) on bacterial community structure was studied in soil microcosms amended with a particulate resource (sterile wheat roots) or a soluble resource (a solution of various organic compounds). Sterilized soil was reinoculated with mixed soil bacteria (obtained by filtering and dilution) or with bacteria and protozoa. Denaturing gradient gel electrophoresis (DGGE) of PCR amplifications of 16S rRNA gene fragments, as well as community level physiological profiling (Biolog plates), suggested that the mixed protozoan community had significant effects on the bacterial community structure. Excising and sequencing of bands from the DGGE gels indicated that high-G+C gram-positive bacteria closely related to Arthrobacter spp. were favored by grazing, whereas the excised bands that decreased in intensity were related to gram-negative bacteria. The percentages of intensity found in bands related to high G+C gram positives increased from 4.5 and 12.6% in the ungrazed microcosms amended with roots and nutrient solution, respectively, to 19.3 and 32.9% in the grazed microcosms. Protozoa reduced the average bacterial cell size in microcosms amended with nutrient solution but not in the treatment amended with roots. Hence, size-selective feeding may explain some but not all of the changes in bacterial community structure. Five different protozoan isolates (Acanthamoeba sp., two species of Cercomonas, Thaumatomonas sp., and Spumella sp.) had different effects on the bacterial communities. This suggests that the composition of protozoan communities is important for the effect of protozoan grazing on bacterial communities.

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KW - FRESH-WATER

KW - NAKED AMEBAS

KW - RELATIVE ABUNDANCE

KW - BARLEY ROOTS

KW - POPULATIONS

KW - SIZE

KW - DIGESTION

KW - RATES

KW - PCR

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SP - 6094

EP - 6105

JO - Applied and Environmental Microbiology

JF - Applied and Environmental Microbiology

SN - 0099-2240

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ER -