title: RNA extraction from cheese for analysis of in situ gene expression of Lactococcus lactis.
abstract: OBJECTIVE
  The isolation of high-quality RNA from cheese is a prerequisite for analysis of in situ gene expression of dairy micro-organisms.
  
  
  RESULTS
  A method for rapid isolation of bacterial cells from cheese using cold citrate buffer followed by mechanical cell disruption was developed. RNA was extracted from experimental ultrafiltration (UF) cheeses (at 2, 8, 24 h, 7 and 14 days) and from Cheddar cheese (from 1 day to 1 year). The quantity and quality of the extracted RNA was assessed. The transcript abundance of seven genes (tuf, gapB, purM, cysK, ldh, cit and gyrA) was estimated by reverse transcription real-time PCR. In UF cheeses, the quantity of RNA extracted increased from 0.2 to 24 microg g(-1), with an RNA Integrity Number (RIN) above 9. In the experimental Cheddar cheeses, the RNA extraction yield decreased from 67.7 microg g(-1) after 1 day to 23.7 microg g(-1) after 6 months, with RIN value above 9 during the first month. The transcript abundance of the seven genes demonstrated metabolic activity of lactococci after several weeks of ripening in both cheeses.
  
  
  CONCLUSIONS
  The method described produced large quantities of high-quality RNA for future whole genome expression studies in cheese.
authors.affiliation: UMR1253, Science et Technologie du Lait et de l'OEuf, INRA, Rennes, France.
authors.forename: V M
authors.initials: VM
authors.lastname: Ulve
authors.forename: C
authors.initials: C
authors.lastname: Monnet
authors.forename: F
authors.initials: F
authors.lastname: Valence
authors.forename: J
authors.initials: J
authors.lastname: Fauquant
authors.forename: H
authors.initials: H
authors.lastname: Falentin
authors.forename: S
authors.initials: S
authors.lastname: Lortal
mesh_terms: D053000:Analytic Sample Preparation Methods / Q000379:methods*; D002611:Cheese / Q000032:analysis* / Q000382:microbiology; D005516:Food Microbiology; D015870:Gene Expression; D005798:Genes, Bacterial / Q000235:genetics; D013294:Lactococcus lactis / Q000235:genetics*; D012329:RNA, Bacterial / Q000032:analysis / Q000302:isolation & purification*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D012329:RNA, Bacterial