title: Oxygen-transfer strategy and its regulation effects in serine alkaline protease production by Bacillus licheniformis.
abstract: The effects of oxygen transfer on the production and product distribution in serine alkaline protease (SAP) fermentation by Bacillus licheniformis and oxygen-transfer strategy in relation to the physiology of the bacilli were investigated on a defined medium with citric acid as sole carbon source in 3.5-dm(3) batch bioreactor systems. By forming a 3 x 3 matrix with the parameters air-inlet rates of Q(O)/V(R) = 0.2, 0.5, 1.0 vvm, and agitation rates of N = 150, 500, 750 min(-1), the effects of oxygen transfer were investigated at nine different conditions. The concentrations of the product SAP and by-products, i.e., neutral protease, alpha-amylase, amino acids, and organic acids, and SAP activities were determined throughout the bioprocess. Among the constant air-flow and agitation-rate fermentations, Q(O)/V(R) = 0.5 vvm, N = 750 min(-1) oxygen-transfer conditions produced maximum SAP activity that was 500 U cm(-3), at t = 37 h. With the increase in Q(O)/V(R) and/or N, Damköhler number that is the oxygen-transfer limitation decreases; and the process passes from oxygen-transfer limited conditions to biochemical-reaction limited conditions. Further increase in SAP activity, A = 680 U cm(-3) was achieved by applying an oxygen-transfer strategy based on the analysis of the data obtained with the constant oxygen-transfer condition experiments, with a step increase in air-inlet rate, from Q(O)/V(R) = 0.2 to Q(O)/V(R) = 0.5 vvm at N = 750 min(-1) constant agitation rate at t = 24 h. Organic acids and amino acids that were excreted to the fermentation medium varied depending on the oxygen-transfer conditions. With the increase in oxygen-transfer rate acetic acid concentration increased; contrarily, with the decrease in the oxygen-transfer rate the TCA-cycle organic acids alpha-ketoglutaric and succinic acids, and gluconic acid were excreted to the fermentation broth; nevertheless, the application of the oxygen-transfer strategy prevented the increase in acetic acid concentration between t = 35-38 h. Under all the oxygen-transfer conditions, the amino acid having the highest concentration and the amino acid that was not excreted to the fermentation broth were lysine and asparagine, respectively; both of which belong to the aspartic acid-group amino acids. Further, this result indicates the requirement of the genetic regulation directed to the aspartic acid-group enzymes for the progress in SAP production in B. licheniformis.
authors.affiliation: Industrial Biotechnology Department of Biotechnology Research Center, Ankara University, Tandoğan, Turkey.
authors.forename: P
authors.initials: P
authors.lastname: Calik
authors.forename: G
authors.initials: G
authors.lastname: Calik
authors.forename: T H
authors.initials: TH
authors.lastname: Ozdamar
mesh_terms: D019342:Acetic Acid / Q000378:metabolism; D000388:Air; D000596:Amino Acids / Q000378:metabolism; D001407:Bacillus / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D018533:Biomass; D019149:Bioreactors; D019343:Citric Acid / Q000378:metabolism; D002952:Citric Acid Cycle / Q000187:drug effects; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism; D005285:Fermentation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism; D010100:Oxygen / Q000008:administration & dosage* / Q000378:metabolism* / Q000494:pharmacology; D019289:Pyruvic Acid / Q000378:metabolism; D012697:Serine Endopeptidases / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D003470:Culture Media; D019343:Citric Acid; D019344:Lactic Acid; D019289:Pyruvic Acid; D012697:Serine Endopeptidases; D019342:Acetic Acid; D010100:Oxygen