L+-lactic acid production from starch by a novel amylolytic Lactococcus lactis subsp. lactis B84.
A new Lactococcus lactis subsp. lactis B84, capable of utilizing starch as a sole carbon source and producing L(+)-lactate, was isolated from spontaneously fermented rye sourdough. Aiming at maximum lactic acid productivity, the components of the media and the cultivation conditions were varied. In MRS-starch medium (with absence of yeast and meat extracts), at 33 degrees C, agitation 200 rpm and pH 6.0 for 6 days complete starch hydrolysis occurred and 5.5 gl(-1) lactic acid were produced from 18 gl(-1) starch. The identification of strain B84 was based on genetic criteria. Amplified ribosomal DNA restriction analysis (ARDRA), PCR with species-specific primers and sequencing of the 16S rDNA proved its species affiliation. Four genes for enzymes, involved in starch degradation were detected in B84 genome: amyL, amyY, glgP and apu, coding cytoplasmic and extracellular alpha-amylases, glycogen phosphorylase and amylopullulanase, respectively. Reverse transcription PCR experiments showed that both genes, encoding alpha-amylases (amyL and amyY) were expressed into mRNAs, whereas apu and glgP were not. Amylase activity assay was performed at different pH and temperatures. The cell-bond amylase proved to be the key enzyme, involved in the starch hydrolysis with maximum activity at 45 degrees C and pH 5.4.
Petrov
Kaloyan
K
Institute of Chemical Engineering, Bulgarian Academy of Sciences, 103 Acad. G. Bonchev Street, 1113 Sofia, Bulgaria.
Urshev
Zoltan
Z
Petrova
Penka
P
D001426:Bacterial Proteins / Q000235:genetics; D003470:Culture Media; D005285:Fermentation; D005433:Flour / Q000382:microbiology; D024981:Glycogen Phosphorylase / Q000235:genetics; D006026:Glycoside Hydrolases / Q000235:genetics; D006868:Hydrolysis; D019344:Lactic Acid / Q000378:metabolism*; D013294:Lactococcus lactis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D015183:Restriction Mapping; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013213:Starch / Q000378:metabolism*; D000516:alpha-Amylases / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D003470:Culture Media; D012336:RNA, Ribosomal, 16S; D019344:Lactic Acid; D013213:Starch; D024981:Glycogen Phosphorylase; D006026:Glycoside Hydrolases; D000516:alpha-Amylases; C082507:amylopullulanase