Tween 80™-induced changes in fatty acid profile of selected mesophilic lactobacilli

Fatty acid profiles are crucial for the functionality and viability of lactobacilli used in food applications. Tween 80™, a common culture media additive, is known to influence bacterial growth and composition. This study investigated how Tween 80™ supplementation impacts the fatty acid profiles of six mesophilic lactobacilli strains (Lacticaseibacillus spp., Limosilactobacillus spp., Lactiplantibacillus plantarum). Analysis of eleven strains revealed 29 distinct fatty acids. Tween 80™ supplementation significantly altered their fatty acid composition. Notably, there was a shift towards saturated fatty acids and changes within the unsaturated fatty acid profile. While some unsaturated fatty acids decreased, there was a concurrent rise in cyclic derivatives like lactobacillic acid (derived from vaccenic acid) and dihydrosterculic acid (derived from oleic acid). This suggests that despite the presence of Tween 80™ as an oleic acid source, lactobacilli prioritize the synthesis of these cyclic derivatives from precursor unsaturated fatty acids. Myristic acid and dihydrosterculic acid levels varied across strains. Interestingly, palmitic acid content increased, potentially reflecting enhanced incorporation of oleic acid from Tween 80™ into membranes. Conversely, cis-vaccenic acid levels consistently decreased across all strains. The observed fatty acid profiles differed from previous studies, likely due to a combination of factors including strain-specific variations and growth condition differences (media type, temperature, harvesting point). However, this study highlights the consistent impact of Tween 80™ on the fatty acid composition of lactobacilli, regardless of these variations. In conclusion, Tween 80™ significantly alters fatty acid profiles, influencing saturation levels and specific fatty acid proportions. This work reveals key factors, including stimulated synthesis of lactobacillic acid, competition for oleic acid incorporation, and strain-specific responses to myristic and dihydrosterculic acids. The consistent reduction in cis-vaccenic acid and the presence of cyclic derivatives warrant further investigation to elucidate their roles in response to Tween 80™ supplementation.

Roles of flavoprotein oxidase and the exogenous heme- and quinone-dependent respiratory chain in lactic acid bacteria

Lactic acid bacteria (LAB) are a type of bacteria that convert carbohydrates into lactate through fermentation metabolism. While LAB mainly acquire energy through this anaerobic process, they also have oxygen-consuming systems, one of which is flavoprotein oxidase and the other is exogenous heme- or heme- and quinone-dependent respiratory metabolism. Over the past two decades, research has contributed to the understanding of the roles of these oxidase machineries, confirming their suspected roles and uncovering novel functions. This review presents the roles of these oxidase machineries, which are anticipated to be critical for the future applications of LAB in industry and comprehending the virulence of pathogenic streptococci.

Formulation of Chemically Defined Media and Growth Evaluation of Ligilactobacillus salivarius ZJ614 and Limosilactobacillus reuteri ZJ625

Lactic acid bacteria are increasingly becoming important dietary supplements due to their health benefits when consumed in adequate quantity. The increasing attention on these important microbes has necessitated an in-depth understanding of their physiological processes, such as nutritional requirements and growth patterns, to better harness their probiotic potentials. This study was carried out to determine the nutritional requirements for the growth of L. salivarius ZJ614 and L. reuteri ZJ625 from a chemically defined medium and evaluate growth kinetics by fitting different sigmoidal growth models. The complete CDM contains 49 nutritional ingredients such as glucose, Tween 80^®, mineral salts, buffers, amino acids, vitamins, and nucleotides at defined concentrations. In addition, the minimal nutritional requirements of the isolates were determined in a series of single-omission experiments (SOEs) to compose the MDM. Growth curve data were generated by culturing in an automated 96-well micro-plate reader at 37°C for 36 h, and photometric readings (optical density: OD₆₀₀) were taken. The data were summarized in tables and charts using Microsoft Excel, while growth evaluation was carried out using open-source software (Curveball) on Python. The results revealed that omission of the amino acids, vitamins, and nucleotides groups resulted in 2.0, 20.17, and 60.24% (for L. salivarius ZJ614) and 0.95, 42.7, and 70.5% (for L. reuteri ZJ625) relative growths, respectively. Elimination of the individual CDM components also indicates varying levels of growth by the strains. The growth curve data revealed LogisticLag2 and Baranyi–Roberts models as the best fits for L. reuteri ZJ625 and L. salivarius ZJ614, respectively. All the strains showed appreciable growth on the CDM and MDM as observed in de Man–Rogosa–Sharpe (MRS) broth. We also described the growth kinetics of L. reuteri ZJ625 and L. salivarius ZJ614 in the CDM, and the best models revealed the estimated growth parameters.

Properties of an acid-tolerant, persistent Cheddar cheese isolate, Lacticaseibacillus paracasei GCRL163

The distinctive flavours in hard cheeses are attributed largely to the activity of nonstarter lactic acid bacteria (NSLAB) which dominate the cheese matrix during maturation after lactose is consumed. Understanding how different strains of NSLAB survive, compete, and scavenge available nutrients is fundamental to selecting strains as potential adjunct starters which may influence product traits. Three Lacticaseibacillus paracasei isolates which dominated at different stages over 63-week maturation periods of Australian Cheddar cheeses had the same molecular biotype. They shared many phenotypic traits, including salt tolerance, optimum growth temperature, growth on N-acetylglucosamine and N-acetylgalactosamine plus delayed growth on D-ribose, carbon sources likely present in cheese due to bacterial autolysis. However, strains 124 and 163 (later named GCRL163) survived longer at low pH and grew on D-tagatose and D-mannitol, differentiating this phenotype from strain 122. When cultured on growth-limiting lactose (0.2%, wt/vol) in the presence of high concentrations of L-leucine and other amino acids, GCRL163 produced, and subsequently consumed lactate, forming acetic and formic acids, and demonstrated temporal accumulation of intermediates in pyruvate metabolism in long-term cultures. Strain GCRL163 grew in Tween 80-tryptone broths, a trait not shared by all L. casei-group dairy isolates screened in this study. Including citrate in this medium stimulated growth of GCRL163 above citrate alone, suggesting cometabolism of citrate and Tween 80. Proteomic analysis of cytosolic proteins indicated that growth in Tween 80 produced a higher stress state and increased relative abundance of three cell envelope proteinases (CEPs) (including PrtP and Dumpy), amongst over 230 differentially expressed proteins.

Effect of Respiratory Growth on the Metabolite Production and Stress Robustness of Lactobacillus casei 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, Lactobacillus casei 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. Cultivation in WPM induced a diauxic growth in both anaerobic and respiratory conditions, and L. casei N87 effectively consumed the lactose and galactose present in WPM. Genomic information suggested that membrane PTS system and tagatose-6-P pathway mediated the metabolism of lactose and galactose in L. casei N87. Respiration did not affect specific growth rate and biomass production, but significantly altered the pyruvate conversion pathways, reducing lactate accumulation and promoting the formation of acetate, acetoin and diacetyl to ensure the redox balance. Ethanol was not produced under either cultivation. Pyruvate oxidase (pox), acetate kinase (ack), α-acetolactate decarboxylase (ald), acetolactate synthase (als) and oxaloacetate decarboxylase (oad) genes were up-regulated under respiration, while L-lactate dehydrogenase (ldh), pyruvate formate lyase (pfl), pyruvate carboxylase (pyc), and phosphate acetyltransferase (pta) were down regulated by oxygen. Transcription analysis was consistent with metabolite production, confirming that POX-ACK and ALS-ALD were the alternative pathways activated under aerobic cultivation. Respiratory growth affected the production of volatile compounds useful for the development of aroma profile in several fermented foods, and promoted the survival of L. casei N87 to oxidative stresses and long-term storage. This study confirmed that the respiration-based technology coupled with cultivation on low-cost medium may be effectively exploited to produce competitive and functional starter and/or adjunct cultures. Our results, additionally, provided further information on the activation and regulation of metabolic pathways in homofermentative LAB grown under respiratory promoting conditions.

Impact of aerobic and respirative life-style on Lactobacillus casei N87 proteome

Lactic acid bacteria (LAB) are used as starter, adjunct and/or probiotic cultures in fermented foods. Several species are recognized as oxygen-tolerant anaerobes, and aerobic and respiratory cultivations may provide them with physiological and technological benefits. In this light, mechanisms involved in the adaptation to aerobic and respiratory (supplementation with heme and menaquinone) growth conditions of the O₂-tolerant strain Lactobacillus casei N87 were investigated by proteomics. In fact, in this bacterial strain, respiration induced an increase in biomass yield and robustness to oxidative, long-term starvation and freeze-drying stresses, while high concentrations of dissolved O₂ (dO₂ 60%) negatively affected its growth and cell survival. Proteomic results well paralleled with physiological and metabolic features and clearly showed that aerobic life-style led to a higher abundance of several proteins involved in carbohydrate metabolism and stress response mechanisms and, concurrently, impaired the biosynthesis of proteins involved in nucleic acid formation and translation processes, thus providing evidence at molecular level of the significant damage to L.casei N87 fitness. On the contrary, the activation of respiratory pathways due to heme and menaquinone supplementation, led to a decreased amount of chaperones and other stress related proteins. These findings confirmed that respiration reduced oxidative stress condition, allowing to positively modulate the central carbohydrate and energy metabolism and improve growth and stress tolerance features. Results of this study could be potentially functional to develop competitive adjunct and probiotic cultures effectively focused on the improvement of quality of fermented foods and the promotion of human health.