title: Storage conditions of intestinal microbiota matter in metagenomic analysis.
abstract: BACKGROUND
  The structure and function of human gut microbiota is currently inferred from metagenomic and metatranscriptomic analyses. Recovery of intact DNA and RNA is therefore a critical step in these studies. Here, we evaluated how different storage conditions of fecal samples affect the quality of extracted nucleic acids and the stability of their microbial communities.
  
  
  RESULTS
  We assessed the quality of genomic DNA and total RNA by microcapillary electrophoresis and analyzed the bacterial community structure by pyrosequencing the 16S rRNA gene. DNA and RNA started to fragment when samples were kept at room temperature for more than 24 h. The use of RNAse inhibitors diminished RNA degradation but this protection was not consistent among individuals. DNA and RNA degradation also occurred when frozen samples were defrosted for a short period (1 h) before nucleic acid extraction. The same conditions that affected DNA and RNA integrity also altered the relative abundance of most taxa in the bacterial community analysis. In this case, intra-individual variability of microbial diversity was larger than inter-individual one.
  
  
  CONCLUSIONS
  Though this preliminary work explored a very limited number of parameters, the results suggest that storage conditions of fecal samples affect the integrity of DNA and RNA and the composition of their microbial community. For optimal preservation, stool samples should be kept at room temperature and brought at the laboratory within 24 h after collection or be stored immediately at -20°C in a home freezer and transported afterwards in a freezer pack to ensure that they do not defrost at any time. Mixing the samples with RNAse inhibitors outside the laboratory is not recommended since proper homogenization of the stool is difficult to monitor.
authors: Digestive System Research Unit, Vall d'Hebron Institut de Recerca, Ciberehd, Barcelona, Spain.
authors: Silvia
authors: S
authors: Cardona
authors: Anat
authors: A
authors: Eck
authors: Montserrat
authors: M
authors: Cassellas
authors: Milagros
authors: M
authors: Gallart
authors: Carmen
authors: C
authors: Alastrue
authors: Joel
authors: J
authors: Dore
authors: Fernando
authors: F
authors: Azpiroz
authors: Joaquim
authors: J
authors: Roca
authors: Francisco
authors: F
authors: Guarner
authors: Chaysavanh
authors: C
authors: Manichanh
mesh_terms: D058448:Biota; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D019075:Electrophoresis, Capillary; D005243:Feces / Q000382:microbiology; D041981:Gastrointestinal Tract / Q000382:microbiology*; D006801:Humans; D054892:Metagenome / Q000235:genetics*; D056186:Metagenomics / Q000379:methods* / Q000592:standards; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013048:Specimen Handling / Q000379:methods*; D013696:Temperature; D013997:Time Factors
chemical_list: D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S