title: Effect of natamycin on the enumeration, genetic structure and composition of bacterial community isolated from soils and soybean rhizosphere.
abstract: Natamycin is commonly used to control fungal growth on agar media used for bacterial enumeration or strain isolation. However, there is no conclusive report on the possible effect of this antibiotic on bacterial growth or on the diversity of the recovered soil bacteria. Therefore, the possible effects of natamycin on the numbers of bacteria isolated at 12 degrees C from three different soils and soybean rhizosphere soil were investigated using natamycin concentrations ranging from 0 to 200 mg l(-1). Our results demonstrate that natamycin concentrations, which inhibit the growth of fungi on the media, have a small but significant inhibitory effect on the number of bacterial colony forming units. A natamycin concentration of 50-200 mg l(-1) is required for an efficient control of fungal growth on media in our experimental conditions depending on the soil type. Bacterial community structure was assessed on culturable cells (cells washed from enumeration plates: plate-wash approach) obtained at 12 degrees C from soybean rhizosphere soil by performing Ribosomal Intergenic Spacer Analysis (RISA) fingerprinting. We demonstrate that all natamycin concentrations used alter the structure of the recovered, culturable bacterial community, compared to control without natamycin. Using ARDRA (amplification of the 16S rDNA gene and restriction analysis) genotyping of individual isolates, some differences were observed between the bacterial isolates obtained in the presence or absence of natamycin. Bacterial isolates recovered in the presence of natamycin are more tolerant (maximal growth rate and lag phase) to this compound than those isolated without natamycin, indicating a possible selection of resistant strains. Therefore, high concentration of natamycin cannot be used for isolation of bacterial strains with the aim of studying biodiversity and could bias a selection of strains for practical applications.
authors.affiliation: INRA/CMSE, UMR 1229 Microbiologie et Géochimie des Sols, 17 rue de Sully, BP 86510, 21065 Dijon, France.
authors.forename: Mohamed Ahmed Nasr
authors.initials: MA
authors.lastname: Mohamed
authors.forename: Lionel
authors.initials: L
authors.lastname: Ranjard
authors.forename: Colette
authors.initials: C
authors.lastname: Catroux
authors.forename: Gérard
authors.initials: G
authors.lastname: Catroux
authors.forename: Alain
authors.initials: A
authors.lastname: Hartmann
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D015169:Colony Count, Microbial; D016172:DNA Fingerprinting; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D014644:Genetic Variation; D010866:Natamycin / Q000494:pharmacology*; D018517:Plant Roots / Q000382:microbiology; D025341:Principal Component Analysis; D012336:RNA, Ribosomal, 16S / Q000737:chemistry / Q000235:genetics; D012988:Soil Microbiology; D013025:Glycine max / Q000382:microbiology
chemical_list: D000935:Antifungal Agents; D004269:DNA, Bacterial; D021903:DNA, Ribosomal Spacer; D012336:RNA, Ribosomal, 16S; D010866:Natamycin; D004262:DNA Restriction Enzymes