Modern approaches for isolation, selection, and improvement of bacterial strains for fermentation applications

Johansen, Eric; Øregaard, Gunnar; Sørensen, Kim I.; Derkx, Patrick

doi:10.1016/b978-1-78242-015-6.00010-4

Cited by 14 publications

(18 citation statements)

References 31 publications

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“…However, the use of recombinant DNA technology in the food industry is controversial, and genetically modified lactic acid bacteria for yoghurt production have not been brought to market. The reasons are numerous and include a general skepticism among consumers, the burdensome regulatory landscape, and the labeling requirements imposed as part of consumer information in some parts of the world (38). Classic mutants, on the other hand, can be used without additional regulatory approval and without requiring specific labeling.…”

Section: Discussionmentioning

confidence: 99%

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Enhancing the Sweetness of Yoghurt through Metabolic Remodeling of Carbohydrate Metabolism in Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus

Sørensen

Curic-Bawden²,

Junge

et al. 2016

Appl Environ Microbiol

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Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus are used in the fermentation of milk to produce yoghurt. These species normally metabolize only the glucose moiety of lactose, secreting galactose and producing lactic acid as the main metabolic end product. We used multiple serial selection steps to isolate spontaneous mutants of industrial strains of S. thermophilus and L. delbrueckii subsp. bulgaricus that secreted glucose rather than galactose when utilizing lactose as a carbon source. Sequencing revealed that the S. thermophilus strains had mutations in the galKTEM promoter, the glucokinase gene, and genes encoding elements of the glucose/mannose phosphotransferase system (PTS). These strains metabolize galactose but are unable to phosphorylate glucose internally or via the PTS. The L. delbrueckii subsp. bulgaricus mutants had mutations in genes of the glucose/mannose PTS and in the pyruvate kinase gene. These strains cannot grow on exogenous glucose but are proficient at metabolizing internal glucose released from lactose by ␤-galactosidase. The resulting strains can be combined to ferment milk, producing yoghurt with no detectable lactose, moderate levels of galactose, and high levels of glucose. Since glucose tastes considerably sweeter than either lactose or galactose, the sweetness of the yoghurt is perceptibly enhanced. These strains were produced without the use of recombinant DNA technology and can be used for the industrial production of yoghurt with enhanced intrinsic sweetness and low residual levels of lactose. IMPORTANCEBased on a good understanding of the physiology of the lactic acid bacteria Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, we were able, by selecting spontaneously occurring mutants, to change dramatically the metabolic products secreted into the growth medium. These mutants consume substantially more of the lactose, metabolize some of the galactose, and secrete the remaining galactose and most of the glucose back into the milk. This allows production of yoghurt with very low lactose levels and enhanced natural sweetness, because humans perceive glucose as sweeter than either lactose or galactose. Modern yoghurt production begins with pasteurization of milk, followed by inoculation and fermentation by commercially prepared starter cultures containing strains of the lactic acid bacteria Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (1). In order to satisfy consumer demands regarding appearance, sweetness, texture, and flavor, a number of additional ingredients may be added, including natural or artificial colors, sucrose or artificial sweeteners, texturizing agents, and fruit preparations (2). Today, yoghurt may contain 5 to 12% (wt/vol) added sucrose in addition to the natural sugars (lactose and galactose) already present, resulting in sugar contents that rival those of soft drinks and tarnishing the image of yoghurt as a healthy food. In addition, the potential for gastrointestinal discom...

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Section: Discussionmentioning

confidence: 99%

“…Metabolic rerouting does not necessarily require the use of recombinant DNA technology (38,39). Based on a good understanding of the physiology of the lactic acid bacteria S. thermophilus and L. delbrueckii subsp.…”

Section: Discussionmentioning

confidence: 99%

Enhancing the Sweetness of Yoghurt through Metabolic Remodeling of Carbohydrate Metabolism in Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus

Sørensen

Curic-Bawden²,

Junge

et al. 2016

Appl Environ Microbiol

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“…Conventional strain safety assessments are based on culture-dependent methods like serotyping and phage typing or molecular techniques like PCR amplification and restriction digestion [21], and additional insights into the genetic basis of strain safety can be provided by WGS [22]. For this assessment, different tools are developed to screen for genomes with the presence of virulence factors and for antibiotic resistance genes.…”

Section: Other Available Tools To Assess the Safety Of Fcmentioning

confidence: 99%

Regulatory and Safety Requirements for Food Cultures

et al. 2017

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The increased use of food cultures to ferment perishable raw materials has potentiated the need for regulations to assess and assure the safety of food cultures and their uses. These regulations differ from country to country, all aimed at assuring the safe use of food cultures which has to be guaranteed by the food culture supplier. Here we highlight national differences in regulations and review a list of methods and methodologies to assess the safety of food cultures at strain level, at production, and in the final product.

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“…Changes in consumer preferences toward less additives and artificial ingredients in fermented products put pressure on companies engaged in the production of starters to expand their strain portfolio to satisfy these demands ( Johansen et al, 2015 ). However, there is a general consensus that the biodiversity of available commercial starters is relatively small to develop defined starter blends for novel applications.…”

Section: Introductionmentioning

confidence: 99%

Adaptive Evolution of Industrial Lactococcus lactis Under Cell Envelope Stress Provides Phenotypic Diversity

et al. 2018

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Lactococcus lactis is widely used as a starter in the manufacture of cheese and fermented milk. Its main role is the production of lactic acid, but also contributes to the sensory attributes of cheese. Unfortunately, the diversity of suitable strains to be commercialized as dairy starters is limited. In this work, we have applied adaptive evolution under cell envelope stress (AE-CES) as means to provide evolved L. lactis strains with distinct physiological and metabolic traits. A total of seven strains, three of industrial origin and four wild nisin Z-producing L. lactis, were exposed to subinhibitory concentrations of Lcn972, a bacteriocin that triggers the cell envelope stress response in L. lactis. Stable Lcn972 resistant (Lcn972R) mutants were obtained from all of them and two mutants per strain were further characterized. Minimal inhibitory Lcn972 concentrations increased from 4- to 32-fold compared to their parental strains and the Lcn972R mutants retained similar growth parameters in broth. All the mutants acidified milk to a pH below 5.3 with the exception of one that lost the lactose plasmid during adaptation and was unable to grow in milk, and two others with slower acidification rates in milk. While in general phage susceptibility was unaltered, six mutants derived from three nisin Z producers became more sensitive to phage attack. Loss of a putative plasmid-encoded anti-phage mechanism appeared to be the reason for phage susceptibility. Otherwise, nisin production in milk was not compromised. Different inter- and intra-strain-dependent phenotypes were observed encompassing changes in cell surface hydrophobicity and in their autolytic profile with Lcn972R mutants being, generally, less autolytic. Resistance to other antimicrobials revealed cross-protection mainly to cell wall-active antimicrobials such as lysozyme, bacitracin, and vancomycin. Finally, distinct and shared non-synonymous mutations were detected in the draft genome of the Lcn972R mutants. Depending on the parental strain, mutations were found in genes involved in stress response, detoxification modules, cell envelope biogenesis and/or nucleotide metabolism. As a whole, the results emphasize the different strategies by which each strain becomes resistant to Lcn972 and supports the feasibility of AE-CES as a novel platform to introduce diversity within industrial L. lactis dairy starters.

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Modern approaches for isolation, selection, and improvement of bacterial strains for fermentation applications

Cited by 14 publications

References 31 publications

Enhancing the Sweetness of Yoghurt through Metabolic Remodeling of Carbohydrate Metabolism in Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus

Enhancing the Sweetness of Yoghurt through Metabolic Remodeling of Carbohydrate Metabolism in Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus

Regulatory and Safety Requirements for Food Cultures

Adaptive Evolution of Industrial Lactococcus lactis Under Cell Envelope Stress Provides Phenotypic Diversity

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