Growth fitness, heme uptake and genomic variants in mutants of oxygen-tolerant Lacticaseibacillus casei and Lactiplantibacillus plantarum strains.

Adaptive Laboratory Evolution (ALE) is a powerful tool to improve the fitness of industrially relevant microorganisms, because it circumvents some of the problems related to the use of genetically modified strains. In this study, we used an ALE strategy involving serial batch cultivations in aerobic and respiratory conditions to generate spontaneous mutants from the respiration-competent strain Lacticaseibacillus casei N87. Genotypic changes in selected mutants were investigated using whole genome sequencing (WGS).

Effect of Respiratory Growth on the Metabolite Production and Stress Robustness of N87 Cultivated in Cheese Whey Permeate Medium.

Cheese whey permeate (WP) is a low-cost feedstock used for the production of biomass and metabolites from several lactic acid bacteria (LAB) strains. In this study, N87 was cultivated in an optimized WP medium (WPM) to evaluate the effect of anaerobic and respiratory conditions on the growth performances (kinetics, biomass yield), consumption of sugars (lactose, galactose, glucose) and citrate, metabolite production [organic acids, volatile organic compounds (VOCs)] and stress survival (oxidative, heat, freezing, freeze-drying). The transcription of genes involved in the main pathways for pyruvate conversion was quantified through Real Time-PCR to elucidate the metabolic shifts due to respiratory state.

Dynamics of bacterial communities and interaction networks in thawed fish fillets during chilled storage in air.

Thawed hake (Merluccius capensis and M. paradoxus) and plaice (Pleuronectes platessa) fillets were used as a model to evaluate the effect of storage temperature (0 or 10 °C) and biological variability (fish species, lot to lot) on bacterial growth kinetics and microbial successions. Both culture dependent methods (plate counts on non-selective and selective media) and culture independent methods (qPCR and 16S rRNA gene metabarcoding) were used.

Aerobic and respirative growth of heterofermentative lactic acid bacteria: A screening study.

Heterofermentative lactic acid bacteria (76 strains) belonging to Lactobacillus, Leuconostoc and Weissella species which are important in fermentation, spoilage or as probiotics were screened in a factorial experiment for their ability to grow, produce catalase and consume oxygen in aerobiosis or in anaerobiosis, with or without supplementation with hemin and/or menaquinone in a medium containing glucose as a carbohydrate source. Aerobiosis improved growth with a few exceptions. The effect of supplementation with heme and/or menaquinone was strain specific and clear evidence of heme-boosted respiration was found in some cases.

Factors affecting gene expression and activity of heme- and manganese-dependent catalases in Lactobacillus casei strains.

Catalases reduce oxidative stress by degrading hydrogen peroxide to molecular oxygen and water. The presence of heme-dependent or manganese-dependent catalases was observed for a long time in lactic acid bacteria (LAB) but, to date, knowledge on the factors affecting gene expression and enzymatic functionality are limited to a very few strains. In this study, the effect of atmosphere of incubation (not aerated static growth vs aerated shaken growth) and supplementation with Fe, hemin, Mn or their combinations on the catalase production of respiration-competent strain Lactobacillus casei N87 was evaluated using a 2 factorial design.