title: Top-down impact of bacterivorous nematodes on the bacterial community structure: a microcosm study.
abstract: The influence of bacterivorous nematodes (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis, Panagrolaimus paetzoldi) on the development of a bacterial community growing on decaying cordgrass detritus was studied in laboratory microcosm experiments. Cordgrass leaves were incubated on a sediment surface with a natural bacterial mixture containing bacteria from sediment, cordgrass detritus and habitat water. The four nematode species were applied separately to the microcosms; controls remained without nematodes. Samples were taken seven times over a 65-day period. The bacterial community structure was analysed by means of DGGE of the 16S rRNA genes. Multi Dimensional Scaling showed grouping of the samples per treatment. Analysis of Similarities indicated that the differences between treatments were significantly larger than differences within treatments. Our results suggest that nematodes can have a significant structuring top-down influence on the 'pool' of bacteria growing on the detritus, even at low densities. Dissimilarities were similar between all treatments. Differences in bacterial community composition within the treatments with monhysterids (D. meyli, D. oschei and D. dievengatensis) can be explained by species-specific food preferences. Panagrolaimus paetzoldi on the other hand feeds unselectively, and thus affects the bacterial community differently. A top-down effect of the nematodes on the diversity of the bacterial community was only evident under high grazing pressure, i.e. in the presence of P. paetzoldi.
authors.affiliation: Marine Biology Section, Biology Department, Ghent University, Krijgslaan 281 (S8), 9000 Gent, Belgium. Ilse.DeMesel@Ugent.be
authors.forename: Ilse
authors.initials: I
authors.lastname: De Mesel
authors.forename: Sofie
authors.initials: S
authors.lastname: Derycke
authors.forename: Tom
authors.initials: T
authors.lastname: Moens
authors.forename: Katleen
authors.initials: K
authors.lastname: Van der Gucht
authors.forename: Magda
authors.initials: M
authors.lastname: Vincx
authors.forename: Jean
authors.initials: J
authors.lastname: Swings
mesh_terms: D000818:Animals; D001419:Bacteria / Q000235:genetics* / Q000254:growth & development* / Q000302:isolation & purification; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D004783:Environmental Microbiology; D005247:Feeding Behavior; D020387:Food Chain; D020459:Genes, rRNA; D005828:Genetics, Population; D008969:Molecular Sequence Data; D009348:Nematoda / Q000502:physiology*; D009691:Nucleic Acid Denaturation; D006109:Poaceae / Q000382:microbiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S