Absence Of Yeast Extract Research Articles

Lutispora saccharofermentans sp. nov., a mesophilic, non-spore-forming bacterium isolated from a lab-scale methanogenic landfill bioreactor digesting anaerobic sludge, and emendation of the genus Lutispora to include species which are non-spore-forming and mesophilic.

A novel anaerobic, mesophilic, non-spore-forming bacterium (strain m25T) was isolated from methanogenic enrichment cultures obtained from a lab-scale methanogenic landfill bioreactor containing anaerobic digester sludge. Cells were Gram-stain-negative, catalase-positive, oxidase-negative, rod-shaped, and motile by means of a flagellum. The genomic DNA G+C content was 40.11 mol%. The optimal NaCl concentration, temperature and pH for growth were 2.5 g l-1, 35 °C and at pH 7.0, respectively. Strain m25T was able to grow in the absence of yeast extract on glycerol, pyruvate, arginine and cysteine. In the presence of 0.2 % yeast extract, strain m25T grew on carbohydrates and was able to use glucose, cellobiose, fructose, raffinose and galactose. The novel strain could utilize glycerol, urea, pyruvate, peptone and tryptone. The major fatty acids were iso-C15 : 0, C14 : 0, C16 : 0 DMA (dimethyl acetal) and iso-C15 : 0 DMA. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the new isolate was closely related to Lutispora thermophila EBR46T (95.02 % 16S rRNA gene sequence similarity). Genome relatedness was determined using both average nucleotide identity and amino acid identity analyses, the results of which both strongly supported that strain m25T belongs to the genus Lutispora. Based on its unique phylogenetic features, strain m25T is considered to represent a novel species within the genus Lutispora. Moreover, based on its unique physiologic features, mainly the lack of spore formation, a proposal to amend the genus Lutispora is also provided to include the non-spore-forming and mesophilic species. Lutispora saccharofermentans sp. nov. is proposed. The type strain of the species is m25T (=DSM 112749T=ATCC TSD-268T).

Comparison of peaks in the matrix-assisted laser desorption ionization time-of-flight mass spectrometry spectra of Staphylococcus aureus grown on various blood agar plates

Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) is routinely used for bacterial identification in clinical laboratories. Bacterial protein expression may differ according to their growth conditions, especially the culture medium composition. We aimed to study the peak variations of Staphylococcus aureus grown on various blood agar plates (BAP), especially phenol-soluble modulin-mec (PSM-mec) peak (m/z 2409) associated with mecA gene conferring methicillin resistance. Methicillin-resistant S. aureus (MRSA) ATCC 43300 and eight clinical MRSA isolates were cultured on various commercial BAPs including tryptic soy agar-based BAPs, Columbia agar-based BAP and in-house BAPs with the addition of yeast extract. Analysis of the MALDI-TOF peaks of S. aureus, cultured on various BAPs, revealed the peak intensities of low-molecular weight proteins to vary depending on the composition of BAPs, especially the presence or absence of yeast extract. Especially, the PSM-mec and delta-toxin peaks showed low intensity for S. aureus ATCC 43300 and clinical isolates. No significant differences were found in the number of peaks, but some peaks had lower intensity, corresponding to the medium containing yeast extract, in low-mass region (<m/z 4000). BAPs based on tryptic soy agar rather than Columbia agar seems to be appropriate for the detection of PSM-mec, a methicillin resistance marker of S. aureus and delta-toxin, an agr function indicator.

Production of rhamnolipids by the Thermoanaerobacter sp. CM-CNRG TB177 strain isolated from an oil well in Mexico.

This study aimed to produce and characterize biosurfactants using the Thermoanaerobacter sp. CM-CNRG TB177 strain isolated from an oil field in Mexico, as well as assessing the influence of different carbon and nitrogen sources on the capacity of the produced surfactant to reduce the surface tension of water. The thin-layer chromatography (TLC) revealed that the obtained extract corresponds to a mono-rhamnolipid; the results of the ultra-performance-liquid chromatography/mass spectrometry (UPLC/MS) analysis revealed that the Thermoanaerobacter sp. CM-CNRG TB177 strain produces a mixture of three rhamnolipids, whose masses correspond to mono-rhamnolipid. The rhamnolipids mixture obtained using 2.5% molasses as carbon source diminished the surface tension of water to 29.67 mNm-1, indicating that the concentration of molasses influenced the capacity of the produced surfactant to reduce the surface tension of water. Also, the microorganism was not capable of growing in the absence of yeast extract as nitrogen source. To the best of our knowledge, the presented results describe for the first time the nature of the biosurfactant produced by a bacterium of the Thermoanaerobacter genus.Key points• Thermoanaerobacter sp. CM-CNRG TB177 produces biosurfactants, and its glycolipid nature is described for the first time.• The HPLC analysis revealed a mixture of three rhamnolipid congeners, and UPLC/MS analysis determined that two of the congeners are the rhamnolipids Rha-C8-C10 and Rha-C12-C10.• The lowest surface tension of 29.67 mNm-1 was obtained with molasses as source of carbon at a 2.5% concentration.

Machine learning predicts and provides insights into milk acidification rates of Lactococcus lactis.

Lactococcus lactis strains are important components in industrial starter cultures for cheese manufacturing. They have many strain-dependent properties, which affect the final product. Here, we explored the use of machine learning to create systematic, high-throughput screening methods for these properties. Fast acidification of milk is such a strain-dependent property. To predict the maximum hourly acidification rate (Vmax), we trained Random Forest (RF) models on four different genomic representations: Presence/absence of gene families, counts of Pfam domains, the 8 nucleotide long subsequences of their DNA (8-mers), and the 9 nucleotide long subsequences of their DNA (9-mers). Vmax was measured at different temperatures, volumes, and in the presence or absence of yeast extract. These conditions were added as features in each RF model. The four models were trained on 257 strains, and the correlation between the measured Vmax and the predicted Vmax was evaluated with Pearson Correlation Coefficients (PC) on a separate dataset of 85 strains. The models all had high PC scores: 0.83 (gene presence/absence model), 0.84 (Pfam domain model), 0.76 (8-mer model), and 0.85 (9-mer model). The models all based their predictions on relevant genetic features and showed consensus on systems for lactose metabolism, degradation of casein, and pH stress response. Each model also predicted a set of features not found by the other models.

Production and Nutritional Composition of King Oyster Culinary-Medicinal Mushroom Pleurotus eryngii (Agaricomycetes) Biomass from Brazil

The present study aimed to evaluate the nutritional composition and production of mycelial biomass of Pleurotus eryngii in different culture media, formulated with infusion of purple-skinned sweet potato, glucose concentrations, and the presence or absence of yeast extract. The mushroom was grown for 15 days at 25°C and 150 rpm. The best production of mycelial biomass occurred in the culture medium with 40 g/L of glucose plus yeast extract. At the second cultivation, the fungus entered the exponential growth phase from days 6 until 14. These results indicate that the insertion of nutritional sources in purple-skinned sweet potato media positively influences mycelial biomass production and its nutritional characteristics make it useful for food industry applications.

Effect of inoculum history, growth substrates and yeast extract addition on inhibition of Sulfobacillus thermosulfidooxidans by NaCl

This study reports on the effect of inoculum history, growth substrates, and yeast extract on sodium chloride tolerance of Sulfobacillus thermosulfidooxidans DSM 9293T. The concentrations of NaCl for complete inhibition of Fe2+ oxidation by cells initially grown with ferrous iron sulfate, or tetrathionate, or pyrite as energy sources were 525 mM, 725 mM, and 800 mM, respectively. Noticeably, regardless of NaCl concentrations, oxygen consumption rates of S. thermosulfidooxidans with 20 mM tetrathionate were higher than with 50 mM FeSO4. NaCl concentrations of higher than 400 mM strongly inhibited the iron respiration of S. thermosulfidooxidans. In contrast, the presence of NaCl was shown to stimulate tetrathionate oxidation. This trend was especially pronounced in NaCl-adapted cells where respiration rates at 200 mM NaCl were threefold of those in the absence of NaCl. In NaCl-adapted cultures greater respiration rates for tetrathionate were observed than in non-NaCl-adapted cultures, especially at concentrations ≥ 200 mM NaCl. At concentrations of ≤ 200 mM NaCl, cell growth and iron oxidation were enhanced with the addition of increasing concentrations of yeast extract. Thus, cell numbers in cultures with 0.05% yeast extract were ∼5 times higher than without yeast extract addition. At NaCl concentration as high as 400 mM, however, iron oxidation rates improved compared to control assays without yeast extract, but there was no clear dependence on yeast extract concentrations. The initial growth of bacteria with and without yeast extract in the presence of different NaCl concentrations was shown to impact leaching of copper from chalcopyrite. Copper dissolution was enhanced in the presence of 200 mM NaCl and absence of yeast extract, while the addition of 0.02% yeast extract was shown to promote copper solubilization in the presence of 500 mM NaCl.

Biobutanol production from lignocellulosic biomass using immobilized Clostridium acetobutylicum

Biobutanol produced by acetone-biobutanol-ethanol (ABE) fermentation process has been revisited in the light of its use as “drop in” liquid biofuel to be blended with gasoline. In this study, renewable feedstock like rice straw, sugarcane bagasse and microalgal hydrolysate were used in ABE fermentation via separate hydrolysis and fermentation. Clostridium acetobutylicum ATCC 824 was used as the fermenting organism. Alkali pretreatment followed by enzymatic hydrolysis was used for rice straw and sugarcane bagasse. In batch fermentation, a biobutanol titer and yield of 9.10 g/L and 0.42 mol/mol glucose (0.17 g biobutanol/g glucose), respectively was obtained from rice straw, while sugarcane bagasse achieved a biobutanol titer and yield of 8.40 g/L and 0.40 mol/mol glucose (0.16 g biobutanol/g glucose), respectively. Higher microalgal biomass loading with 3% acid pretreatment severely inhibited fermentation performance. Unhydrolyzed microalgal biomass at a loading of 180 g/L in ABE fermentation resulted in 4.32 g/L biobutanol and 0.09 g biobutanol/g microalgae as yield. C. acetobutylicum was immobilized in polyvinyl alcohol (PVA) for improving the cell loading in fermentation and protect the cells from biobutanol toxicity. With rice straw hydrolysate as a feedstock and in the absence of yeast extract, a biobutanol titer, yield and productivity of 13.80 g/L, 0.90 g/L/h, and 0.58 mol biobutanol/mol glucose (0.23 g biobutanol/g glucose), respectively were obtained. Hence, rice straw is a potential feedstock for biobutanol production for fuel use.

Physiological responses of Chinese hamster ovary cells to a productivity-enhancing yeast extract

Hydrolysates play important roles in enhancing the productivity of recombinant proteins in mammalian cell cultures. Lacking of detailed understanding of the mechanisms, hydrolysate is commonly regarded as an unstable factor which should be used with cautions. A yeast extract (YE) was approved to improve the Fc-fusion protein productivity in a recombinant Chinese hamster ovary (CHO) cell line. To elucidate the responses of cells to hydrolysates, we further elaborate their physiological changes during the processes in the presence and absence of YE. Firstly, cell sizes and the cellular components including dry cell weight, cellular fatty acid, and total cellular protein were increased in the presence of YE. Then, by comparing the extracellular and intracellular concentrations of the main metabolites and their consumption rates, we excluded the possibility of nutrient depletion in the absence of YE and observed a distinct improvement on the net consumption rates of metabolites in the presence of YE. Furthermore, the increase on the contents of intracellular nucleotides illustrated an abundance of the nucleic acid precursors and energy charge for recombinant protein synthesis in the presence of YE. In conclusion, this study systematically elucidated YE enhanced cell mass and capacity, activated substrate and energy metabolism of cells in addition to a boost in product synthesis process. The findings provide valuable information for process optimization and cell engineering.

From waste to treasure: turning activated sludge into bioplastic poly-3-hydroxybutyrate

Large quantity of activated sludge is generated from wastewater treatment but without yet an appropriate deposition. High temperature can lyse the activate sludge so that nitrogen and phosphorus containing nutrients are released. Halomonas CJN was found to grow on the heat lysed activated sludge and glucose for production of bioplastic poly-3-hydroxybutyrate (PHB) in the absence of yeast extract, nitrogen and phosphorus sources as well as trace elements. This reduces the PHB production cost significantly. Furthermore, acetic acid formed from anaerobic fermentation of heat lysed activated sludge can be used to replace glucose for cell growth but not much for PHB production. After construction of an additional PHB synthesis pathway in Halomonas CJN, we can produce PHB entirely from heat lysed activated sludge, reducing production cost of PHB roughly from ¥ 30 000 Yuan/ton to ¥ 20 000 Yuan/ton, thus turning waste activated sludge to valuable raw material resource.

Impact of Phosphate, Potassium, Yeast Extract, and Trace Metals on Chitosan and Metabolite Production by Mucor indicus

In this study the effects of phosphate, potassium, yeast extract, and trace metals on the growth of Mucor indicus and chitosan, chitin, and metabolite production by the fungus were investigated. Maximum yield of chitosan (0.32 g/g cell wall) was obtained in a phosphate-free medium. Reversely, cell growth and ethanol formation by the fungus were positively affected in the presence of phosphate. In a phosphate-free medium, the highest chitosan content (0.42 g/g cell wall) and cell growth (0.66 g/g sugar) were obtained at 2.5 g/L of KOH. Potassium concentration had no significant effect on ethanol and glycerol yields. The presence of trace metals significantly increased the chitosan yield at an optimal phosphate and potassium concentration (0.50 g/g cell wall). By contrast, production of ethanol by the fungus was negatively affected (0.33 g/g sugars). A remarkable increase in chitin and decrease in chitosan were observed in the absence of yeast extract and concentrations lower than 2 g/L. The maximum chitosan yield of 51% cell wall was obtained at 5 g/L of yeast extract when the medium contained no phosphate, 2.5 g/L KOH, and 1 mL/L trace metal solution.

Production of bacteriocin-like inhibitory substance by Bifidobacterium lactis in skim milk supplemented with additives.

Bacteriocins are natural compounds used as food biopreservatives instead of chemical preservatives. Bifidobacterium animalis subsp. lactis (Bifid. lactis) was shown to produce a bacteriocin-like inhibitory substance (BLIS) able to inhibit the growth of Listeria monocytogenes selected as an indicator microorganism. To enhance this production by the strain Bifid. lactis BL 04, skim milk (SM) was used as a fermentation medium either in the presence or in the absence of yeast extract, Tween 80 or inulin as stimulating additives, and the results in terms of bacterial growth and BLIS production were compared with those obtained in a traditional high cost complex medium such as Man, Rogosa and Sharpe (MRS). To this purpose, all the cultivations were carried out in flasks at 200 rpm under anaerobic conditions ensured by a nitrogen flowrate of 1.0 L/min for 48 h, and BLIS production was quantified by means of a modified agar diffusion assay at low values of both temperature and concentration of List. monocytogenes. Although all these ingredients were shown to exert positive influence on BLIS production in both media, yeast extract and SM were by far the best ingredient and the best medium, respectively, allowing for a BLIS production at the late exponential phase of 2000 AU/ml.

Optimization of the performance of a thermophilic biotrickling filter for α-pinene removal from polluted air

Biodegradation of α-pinene was investigated in a biological thermophilic trickling filter, using a lava rock and polymer beads mixture as packing material. Partition coefficient (PC) between α-pinene and the polymeric material (Hytrel G3548 L) was measured at 50°C. PCs of 57 and 846 were obtained between the polymer and either the water or the gas phase, respectively. BTF experiments were conducted under continuous load feeding. The effect of yeast extract (YE) addition in the recirculating nutrient medium was evaluated. There was a positive relationship between α-pinene biodegradation, CO2 production and YE addition. A maximum elimination capacity (ECmax) of 98.9 g m−3 h−1 was obtained for an α-pinene loading rate of about 121 g m−3 h−1 in the presence of 1 g L−1 YE. The ECmax was reduced by half in the absence of YE. It was also found that a decrease in the liquid flow rate enhances α-pinene biodegradation by increasing the ECmax up to 103 g m−3 h−1 with a removal efficiency close to 90%. The impact of short-term shock-loads (6 h) was tested under different process conditions. Increasing the pollutant load either 10- or 20-fold resulted in a sudden drop in the BTF's removal capacity, although this effect was attenuated in the presence of YE.

Ranking the significance of fermentation conditions on the volatile organic compounds of Tuber melanosporum fermentation system by combination of head-space solid phase microextraction and chromatographic fingerprint similarity analysis

Tuber melanosporum is highly appreciated in culinary contexts due to its unique and characteristic aroma. T. melanosporum fermentation has been established as a promising alternative for fruiting bodies to produce volatile organic compounds (VOCs). In this work, a technique using a combination of chromatographic fingerprint similarity analysis, head-space solid phase microextraction and gas chromatography was developed to rank the significance of fermentation conditions on the VOCs profile during T. melanosporum fermentation. Omission tests indicated that the absence of major carbon source (i.e., sucrose) in the fermentation media had the most significant effect on the profile of VOCs, followed by the absence of yeast extract or peptone. Consideration of the culture conditions revealed that VOCs produced was the most significantly affected by temperature. These results indicated that it is possible to adjust the aroma of truffles via fermentation process control.

Characterization of the extracellular biodemulsifier of Bacillus mojavensis XH1 and the enhancement of demulsifying efficiency by optimization of the production medium composition

The demulsifying bacterium XH1 was identified as a Bacillus mojavensis by the 16S rDNA gene. The extracellular biodemulsifier produced by this species was purified by ethanol extraction and column chromatography through a sephadex and silicon gel column. Preliminary investigation using UV–vis and TLC indicated that the biodemulsifier had two components a protein and a lipopeptide. All major components of the medium, including the sources of soluble and insoluble carbon, nitrogen, phosphate, and metal ions were investigated to improve the biosynthesis and efficiency of the biodemulsifier. The optimal carbon sources were glucose and liquid paraffin. Glucose participated in the biosynthesis of the demulsifier, while liquid paraffin promoted the lipophilicity and secretion of biosurfactants. The absence of yeast extract, ammonium chloride or phosphate (K2HPO4/KH2PO4) had a negative effect on the production of the biodemulsifier and significantly inhibited its activity. To further enhance the biodemulsifier efficiency, the optimal medium composition was determined using the response surface methodology (RSM) based on the central composite rotation design (CCRD). Using the optimized biodemulsifier production medium: 8.5g/l glucose; 3% (v/v) liquid paraffin; 1.5g/l yeast extract; 3.36g/l NH4Cl and15g/l phosphate, the demulsifying ratio increased 35.5% and biodemulsifier yield increased to 2.07g/l.

Uso de extrato de levedura como fonte de carbono e de mediadores redox, para a degradação anaeróbia de corante azo

O trabalho investigou a influência do uso do extrato de levedura, fonte dos mediadores redox riboflavina e nicotinamida, na remoção de cor de solução de corante azo Drimaren Azul HF-RL em condições anaeróbias. O trabalho envolveu a execução de ensaios em batelada, em frascos-reatores mantidos a 25 ºC, incubados com o azo-corante e lodo anaeróbio na presença e ausência de fontes de carbono (extrato de levedura ou glicose) e de mediadores redox (riboflavina ou extrato de levedura). O monitoramento da variação temporal de cor, a demanda química de oxigênio (DQO) e ácidos graxos voláteis (AGV) mostraram que a adição de extrato de levedura (0,5 g/L) resultou em eficiências de remoção de cor de 80 a 85% nas primeiras 24 horas de incubação, e que os produtos da degradação do azo-corante foram tóxicos para todo o consórcio anaeróbio, o que resultou em baixas eficiências de remoção de DQO na presença e ausência do extrato de levedura. Os resultados indicaram, ainda, que as eficiências de remoção de cor foram inferiores a 30% na presença de apenas glicose (fonte de carbono) ou riboflavina (mediador redox), indicando que o extrato de levedura atuou simultaneamente como fonte de carbono e de mediadores redox.

Enhancing pozzolana colonization by As(III)-oxidizing bacteria for bioremediation purposes

The colonization of pozzolana by an As(III)-oxidizing bacterial consortium was monitored from the first hours of bacterial adhesion to 6 weeks of development under fed-batch conditions, using adapted ultrasonic dislodging and crystal-violet staining procedures to determine the biofilm adhering to the complex surfaces. The effect of temperature, arsenic concentration, and presence or absence of yeast extract (YE) on the amount of biofilm biomass and on the As(III)-oxidation were assessed to test the biofilm's resilience and optimize the colonization. Fed-batch cultures allow twice as much pozzolana colonization as that obtained under batch conditions. In addition, As(III) oxidation and the quantities of biomass under fed-batch culture conditions were the same at 14 degrees C and 25 degrees C. Whereas YE improves (+150%) bacterial adhesion during the first 2 h, its impact in the longer term appears to be less significant-biofilm formation in presence of YE after 5 weeks was no greater than biofilm formation in the absence of YE. Finally, YE involves a drastic (-70%) decrease of As(III) oxidation. Preliminary tests for drinking-water bioremediation revealed the ability of Chéni Arsenic Oxidizing 1 biofilms to remain and retain As(III) oxidation activity at low As(III) concentrations (50 microg l(-1)).

Ferroplasma cupricumulans sp. nov., a novel moderately thermophilic, acidophilic archaeon isolated from an industrial-scale chalcocite bioleach heap

A new species of Archaea was isolated from an industrial mineral sulphide bioleach heap. Strain BH2, a non-motile pleomorphic coccus, was capable of chemomixotrophic growth on ferrous sulphate and yeast extract. Growth was not supported in the absence of yeast extract. Phylogenetic analysis based on the 16S rRNA gene showed that strain BH2 was most closely related to the species Ferroplasma acidiphilum; however, it showed only 95% sequence similarity with this species. Strain BH2 had a temperature optimum of 53.6 degrees C and a temperature range for growth between 22 and 63 degrees C. Thus, it is the first moderately thermophilic member of the genus Ferroplasma. The optimum pH for the growth of the strain occurred between pH 1.0 and 1.2 and the lowest pH at which growth was observed was 0.4. Based on 16S rRNA gene sequence analysis and other physiological characteristics, strain BH2 constitutes a new species within the genus Ferroplasma. The name Ferroplasma cupricumulans is proposed for the new species and strain BH2 (DSM 16651) is proposed as the type strain.

Repressive effects of yeast extract on photoreactivation of Escherichia coli

Photoreactivation of Escherichia coli K12 (IFO 3301), in the presence or absence of yeast extract (YE), was investigated after inactivation by low-pressure UV lamp. An endonuclease sensitive site (ESS) assay was used to determine the UV-induced pyrimidine dimers in the genome of E. coli, while a colony-forming ability (CFA) test was also used to examine the survival ratio of E. coli. The YE solution reduced the CFA recovery at a final concentration of 125 mg/L. A dialysis of the YE solution indicated that the YE fraction (with nominal molecular weight >1,000 and <3,500) was effective at repressing the CFA recovery. Interestingly, the repair of ESS was equivalent regardless of the presence of the YE dialysate, while the CFA recovery was significantly repressed in the presence of YE. It was, therefore, suggested that YE components, probably with molecular weights of 1,000-3,500, were effective at repressing the CFA recovery of E. coli without affecting the ESS repair during photoreactivation.

Effect of yeast extract on growth and metabolism of H2-utilizing acetogenic bacteria from the human colon.

The aim of this work was to determine the effect of yeast extract and of its vitamin contents on autotrophic and heterotrophic growth and metabolism of four acetogenic bacteria from the human colon. Yeast extract exerted a stimulatory effect on autotrophic growth of the colonic acetogens, but concentration of this compound above 1-2 g. L-1 in the medium did not enhance utilization of H2/CO2. Vitamins provided by yeast extract were shown to be essential cofactors of the reductive pathway of acetate synthesis except for one Clostridium strain. Yeast extract was also necessary to maintain heterotrophic growth and acetate synthesis from glucose in acetogenic species, except in the Streptococcus strain. In the absence of yeast extract, vitamins could efficiently restore glucose fermentation via acetate. The reductive and oxidative pathways of acetate synthesis might, therefore, depend on vitamin cofactors supplied by yeast extract in most of the human acetogenic bacteria. Non-vitaminic factors appeared also to be involved in the metabolism of some of these acetogenic species.

L-lactic acid production from whole wheat flour hydrolysate using strains of Lactobacilli and Lactococci

A whole wheat flour containing bran and gluten was hydrolyzed by a commercial mixed-amylase preparation and fermented to lactic acid by two Lactococcus lactis strains and two Lactobacillus delbrueckii strains. All fermentations were kept at a constant pH of 6.0 except for one case in which the initial pH was 5.85 and then was not controlled further, thereby resulting in only 3.3 g l −1 of lactate produced. The yield of lactate based on total sugar was 80–90% for three of the strains whereas the yield for L. delbrueckii ssp. bulgaricus was much lower. The productivities and yields increased with the addition of yeast extract for all strains, but the effect varied. Lactococcus lactis ssp. lactis ATCC 19435 showed almost the same productivity (3.0 and 3.3 g l −1 h −1) without and with yeast extract, respectively. All four organisms produced mainly l-lactate. The Lactococci produced 100% l-lactate in the presence of yeast extract and Lactococcus lactis ssp. lactis ATCC 19435 produced exclusively l-lactate also in the absence of yeast extract.