A NEWLY ANTI-Streptococcus suis BACTERIOCIN PRODUCING STRAIN FROM UNWEANED PIGLETS FECAL MATTER: ISOLATION,PRELIMINARY IDENTIFICATION,AND OPTIMIZATION OF MEDIUM COMPOSITION FOR ENHANCED BACTERIOCIN PRODUCTION

A newly isolated anti-Streptococcus suis bacteriocin-producing strain LPL1-5 was obtained from healthy unweaned piglets' fecal matter, and was designated as Lactobacillus pentosus LPL1-5 based on morphology, biochemical properties, and 16S rDNA sequencing analysis. The medium composition for enhanced bacteriocin production by L. pentosus LPL1-5 was optimized by statistical methodology. Yeast extract, K₂HPO₄ · 3H₂O, and MnSO₄ · H₂O were identified as significant components influencing pentocin LPL1-5 production using the Plackett–Burman method. Response surface methodology was applied for further optimization. The concentrations of medium components for enhanced pentocin LPL1-5 production were as follows (g/L): lactose 20.00, tryptone 10.00, beef extract 10.00, yeast extract 14.00, MnSO₄ · H₂O 0.84, K₂HPO₄ · 3H₂O 4.92, triammonium citrate 2.00, Na-acetate 5.00, MgSO₄ · 7H₂O 0.58, Tween 80 1.00. Under the optimized condition, a value of 3154.65 ± 27.93 IU/mL bacteriocin activity was achieved, which was 4.2-fold that of the original medium.     

Effects of <Emphasis Type="Italic">Lactobacillus buchneri</Emphasis> and <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> on fermentation,aerobic stability,bacteria diversity and ruminal degradability of alfalfa silage

Silages are important feedstuffs. Homofermentative lactic acid bacterial inoculants are often used to control silage fermentation. However, some research pointed out those homofermentative lactic acid bacteria (LAB) impaired the aerobic stability of wheat, sorghum, and corn silages. Adding heterofermentative LAB can produce more acetic acid, thereby stabilizing silages during aerobic exposure. Alfalfa is difficult to ensile. The present work was to study the effects of L. buchneri (heterofermentative LAB), alone or in combination with L. plantarum (homofermentative LAB) on the fermentation, aerobic stability, bacteria diversity and ruminal degradability of alfalfa silage. After 90 days ensiling, the pH, NH₃-N/TN, butyric acid content and molds counts of control were the highest. The inoculated silages had more lactic acid, acetic acid content and more lactic acid bacteria than the control. Inoculating LAB inhibited harmful microorganisms, such as Enterobacterium and Klebsiella pneumoniae. The L. buchneri + L. plantarum-inoculated silage had more acetic acid and less yeasts than other three treatments (P < 0.05), and lower NH₃-N/TN than control (P < 0.05). The CO₂ production of L. buchneri + L. plantarum-inoculated silage was less than that of L. plantarum-inoculated silage (P < 0.05). Inoculating LAB in alfalfa silages can decrease pH, increase the production of lactic and acetic acids, reduce the number of yeasts and molds, and inhibit Enterobacterium and K. pneumoniae. Inoculating with L. buchneri or L. buchneri + L. plantarum can improve aerobic stability of alfalfa silages. A combination of L. buchneri and L. plantarum is preferable because it enhanced alfalfa silage quality and aerobic stability.     

Interaction between lactic acid bacteria and yeasts in sour-dough using a rheofermentometer

Rheofermentometer assays were used to characterize the leavening of sour-doughs produced using species of lactic acid bacteria (LAB) and yeasts, alone or in combination. Saccharomyces cerevisiae 141 produced the most CO₂ and ethanol whereas S. exiguus M14 and Lactobacillus brevis subsp. lindneri CB1 contributed poorly to leavening and gave sour-doughs without porosity. In comparison with that seen in sour-dough produced with yeast alone, yeast fermentation with heterofermentative LAB present was faster whereas that with homofermentative LAB (L. plantarum DC400, L. farciminis CF3) present was slower and produced more CO₂. Combining L. brevis subsp. lindneri CB1 with S. cerevisiae 141 decreased bacterial cell numbers and souring activity. However, addition of fructose to the sour-dough overcame these problems as well as activating S. cerevisiae 141.The authors are with the Institute of Dairy Microbiology, Faculty of Agriculture, University of Perugia, S. Costanzo, 06126 Perugia, Italy     

戊糖乳杆菌发酵培养基氮源条件的优化

对戊糖乳杆菌发酵培养基的氮源条件进行了优化。通过单因素实验及响应面分析优化利用木糖高产乳酸的戊糖乳杆菌发酵培养基的不同氮源组合。优化得到的牛肉膏与柠檬酸氢二铵复合的最佳组成为牛肉膏17.72 g/L,柠檬酸氢二铵1.91 g/L,得到乳酸实际最大产量42.37 g/L。添加玉米浆与酵母粉和无机氮源复合的最佳组成为玉米浆46.54 g/L,酵母粉21.95 g/L,柠檬酸氢二铵9.95 g/L,可得到乳酸最大产量41.06 g/L。通过响应面优化减少了有机氮源的种类。牛肉膏与柠檬酸氢二铵的复合得到了更高的乳酸产量,且减少了有机氮源用量,节约了成本。玉米浆与酵母粉的复合解决了单一玉米浆造成的木糖利用速率过低的问题,同样得到较高浓度的乳酸。     

Characterization of dominant lactic acid bacteria isolated from São Jorge cheese, using biochemical and ribotyping methods

Aims: To identify, using phenotypic and genotypic methods, the dominant lactic acid bacteria (LAB) present in São Jorge cheese – one of the 11 Portuguese cheeses currently bearing an Appéllation d’Origine Protegée status. Methods and Results: A total of 225 isolates from milk, curd and cheeses throughout ripening were identified to the genus level, 108 to the species level and ten to the strain level. Phenotypic methods indicated that lactobacilli, followed by enterococci, were the dominant bacteria. The most frequently isolated species were Lactobacillus paracasei, Lactobacillus rhamnosus, Enterococcus faecalis and Enterococcus faecium. Ribotyping differentiated three L. paracasei, two E. faecalis and one Lactobacillus plantarum types. Enterococcus spp. exhibited the highest esterase and β-galactosidase activities among all isolates. Conclusions: The dominant LAB in São Jorge cheese are L. paracasei, L. rhamnosus, E. faecalis and E. faecium. Enterococcus likely plays a leading role upon acidification and aroma development in said cheese. Significance and Impact of the Study:  Our results support that a combination of conventional biochemical methods with genotypic methods allows for a thorough characterization and identification of isolates. Despite the limited number of isolates subject to molecular subtyping, a few specific Enterococcus and Lactobacillus strains were found that are promising ones for development of a starter culture. Hence, L. paracasei and E. faecalis are good candidates for a tentative starter culture, designed for manufacturing of São Jorge cheese at large – which takes advantage of actual isolates, in attempts to eventually standardize the quality of said cheese variety.     

Aerobic metabolism and oxidative stress tolerance in the Lactobacillus plantarum group

Aerobic metabolism and response to oxidative stress and starvation were studied in 11 Lactobacillus plantarum, L. paraplantarum and L. pentosus strains in order to assess the impact of aerobic metabolism on the growth and on the stress response. The strains were grown in aerobiosis without supplementation (AE), with hemin (AEH) or with hemin and menaquinone (AEHM) supplementation and in anaerobiosis (AN) in a complex buffered substrate. Growth rate, biomass yield, glucose and O₂ consumption, production of lactic acid and H₂O₂, catalase activity, oxidative and starvation stress tolerance were evaluated. Aerobic growth increased biomass yield in late stationary phase. Further increase in yield was obtained with both hemin (H) and menaquinone (M) addition. With few exceptions, the increase in biomass correlated with the decrease of lactic acid which, however, decreased in anaerobic conditions as well in some strains. Addition of H or H + M increased growth rate for some strains but reduced the duration of the lag phase. H₂O₂ production was found only for aerobic growth with no supplementation due to catalase production when hemin was supplemented. To our knowledge this is the first study in which the advantages of aerobic growth with H or H + M in improving tolerance of oxidative stress and long-term survival is demonstrated on several strains of the L. plantarum group. The results may have significant technological consequences for both starter and probiotic production.     

Production of cholera toxin B subunit in Lactobacillus

The intracellular expression of the B subunit of cholera toxin (CTB) was first achieved in Lactobacillus paracasei LbTGS1.4 with an expression cassette including the P25 promoter of Streptococcus thermophilus combined with the translation initiation region from the strongly expressed L. pentosus d-lactate dehydrogenase gene (ldhD). Secretion of CTB was next attempted in L. paracasei LbTGS1.4 and L. plantarum NCIMB8826 with four different signal sequences from exported proteins of lactic acid bacteria (Lactococcus lactis Usp45 and PrtP, Enterococcus faecalis unknown protein and S. pyogenes M6 protein). Host-dependent secretion of CTB was clearly observed: whereas none of the secretion cassettes led to detectable CTB in the extracellular fraction of L. paracasei LbTGS1.4, secretion of CTB molecules was clearly achieved with three of the selected signal sequences in L. plantarum NCIMB8826.     

Molecular characterization of lactic acid bacteria recovered from natural fermentation of beet root and carrot Kanji

The lactic acid bacteria (LAB) play an important role in the fermentation of vegetables to improve nutritive value, palatability, acceptability, microbial quality and shelf life of the fermented produce. The LAB associated with beetroot and carrot fermentation were identified and characterized using different molecular tools. Amplified ribosomal DNA restriction analysis (ARDRA) provided similar DNA profile for the 16 LAB strains isolated from beetroot and carrot fermentation while repetitive extragenic palindromic PCR (rep-PCR) genotyping could differentiate the LAB strains into eight genotypes. Thirteen strains represented by five genotypes could be clustered in five distinct groups while three LAB strains exhibiting distinct genotypes remained ungrouped. These genotypes could be identified to be belonging to L. plantarum group by 16S rDNA sequencing. The recAnested multiplex PCR employing species-specific primers for the L. plantarum group members identified the LAB strains of six genotypes to be L. paraplantarum and the other two genotypes to be L. pentosus. Three genotypes of L. paraplantarum were consistently found on the third and sixth day of beetroot fermentation whereas a distinct genotype of L. paraplantarum and L. pentosus appeared predominant on the tenth day. From carrot Kanji two distinct genotypes of L. paraplantarum and one genotype of L. pentosus were identified. REP-PCR DNA fingerprinting coupled with 16S rDNA sequencing and recA-nested multiplex PCR could clearly identify as well as differentiate the diverse L. plantarum group strains involved in the fermentation.     

Enhancing Nutritional Quality of Silage by Fermentation with Lactobacillus plantarum

The present study was aimed to investigate the nutritive profiles, microbial counts and fermentation metabolites in rye, Italian rye-grass (IRG) and barley supplemented with Lactobacillus plantarum under the field condition, and its probiotic properties. After preparation of silage, the content of crude protein (CP), crude ash, acid detergent fiber (ADF), and neutral detergent fiber (NDF), microbes such as lactic acid bacteria (LAB), yeast and fungi counts, and fermentation metabolites lactic acid, acetic acid and butyric acid was assessed. Results indicated that the content of ADF and NDF were significantly varied between rye, IRG and barley mediated silages. The content of CP was increased in L. plantarum supplemented with IRG, but slightly decreased in rye and barley mediated silages. The maximum LAB count was recorded at 53.10 × 10⁷ cfu/g in rye, 16.18 × 10⁷ cfu/g in IRG and 2.63 × 10⁷ cfu/g in barley silages respectively. A considerable number of the yeasts were observed in the IRG silages than the rye silages (P < 0.05). The amount of lactic acid production is higher in L. plantarum supplemented silages as compared with control samples (P < 0.05). It was confirmed that higher amount of lactic acid produced only due to more number of LAB found in the silages. L. plantarum was able to survive at low pH and bile salt and the duodenum passage with the highest percentage of hydrophobicity. Furthermore, the strain was sensitive towards the antibiotics commonly used to maintain the microbes in food industrial setups. In conclusion, supplementation of L. plantarum is most beneficial in rye, IRG and barley silage preparations and probiotic characteristics of L. plantarum was an intrinsic feature for the application in the preparation of animal feeds and functional foods.     

Bioconversion of isoflavone glycosides to aglycones,mineral bioavailability and vitamin B complex in fermented soymilk by probiotic bacteria and yeast

Aim: To study the role of β‐glucosidase producing probiotic bacteria and yeast in the biotransformation of isoflavone glycosides to aglycones, mineral bioavailability and vitamin B complex in fermented soymilk. Methods and Results: Five isolates of probiotic lactic acid bacteria (LAB), Lactobacillus acidophilus B4496, Lactobacillus bulgaricus CFR2028, Lactobacillus casei B1922, Lactobacillus plantarum B4495 and Lactobacillus fermentum B4655 with yeast Saccharomyces boulardii were used to ferment soymilk to obtain the bioactive isoflavones, genistein and daidzein. High‐performance liquid chromatography was used to analyse the concentration of isoflavones. Bioactive aglycones genistein and daidzein after 24 and 48 h of fermentation ranged from 97·49 to 98·49% and 62·71 to 92·31% respectively with different combinations of LAB with yeast. Increase in bioavailability of minerals and vitamin B complex were also observed in fermented soymilk. Conclusions: LAB in combination with yeast S. boulardii has great potential for the enrichment of bioactive isoflavones, enhancing the viability of LAB strains, decreasing the antinutrient phytic acid and increasing the mineral bioavailability in soymilk fermentation. Significance and Impact of the Study: Fermentation of soymilk with probiotic organisms improves the bioavailability of isoflavones, assists in digestion of protein, provides more soluble calcium, enhances intestinal health and supports immune system. Increased isoflavone aglycone content in fermented soymilk improves the biological functionality of soymilk.     

Selenium nanoparticles from Lactobacillus paracasei HM1 capable of antagonizing animal pathogenic fungi as a new source from human breast milk

The current study was performed to develop a simple, safe, and cost-effective technique for the biosynthesis of selenium nanoparticles (SeNPs) from lactic acid bacteria (LAB) isolated from human breast milk with antifungal activity against animal pathogenic fungi. The LAB was selected based on their speed of transforming sodium selenite (Na₂SeO₃) to SeNPs. Out of the four identified LAB isolates, only one strain produced dark red color within 32 h of incubation, indicating that this isolate was the fastest in transforming Na₂SeO₃ to SeNPs; and was chosen for the biosynthesis of LAB-SeNPs. The superior isolate was further identified as Lactobacillus paracasei HM1 (MW390875) based on matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and phylogenetic tree analysis of 16S rRNA sequence alignments. The optimum experimental conditions for the biosynthesis of SeNPs by L. paracasei HM1 were found to be pH (6.0), temperature (35˚C), Na₂SeO₃ (4.0 mM), reaction time (32 h), and agitation speed (160 rpm). The ultraviolet absorbance of L. paracasei-SeNPs was detected at 300 nm, and the transmission electron microscopy (TEM) captured a diameter range between 3.0 and 50.0 nm. The energy-dispersive X-ray spectroscopy (EDX) and the Fourier-transform infrared spectroscopy (FTIR) provided a clear image of the active groups associated with the stability of L. paracasei-SeNPs. The size of L. paracasei-SeNPs using dynamic light scattering technique was 56.91 ± 1.8 nm, and zeta potential value was −20.1 ± 0.6 mV in one peak. The data also revealed that L. paracasei-SeNPs effectively inhibited the growth of Candida and Fusarium species, and this was further confirmed by scanning electron microscopy (SEM). The current study concluded that the SeNPs obtained from L. paracasei HM1 could be used to prepare biological antifungal formulations effective against major animal pathogenic fungi. The antifungal activity of the biologically synthesized SeNPs using L. paracasei HM1 outperforms the chemically produced SeNPs. In vivo studies showing the antagonistic effect of SeNPs on pathogenic fungi are underway to demonstrate the potential of a therapeutic agent to treat animals against major infectious fungal diseases.     

Changes in steady state on introduction of a Lactobacillus contaminant to a continuous culture ethanol fermentation

Lactobacillus paracasei was introduced as a contaminant into a multistage continuous culture ethanol fermentation system at ratios of 1:100, 1:1, and 70:1 with Saccharomyces cerevisiae, but failed to overtake the yeast. None of the inoculation ratios allowed L. paracasei to affect S. cerevisiae in the first fermentor in the multistage system. S. cerevisiae remained constant at ∼3×10⁷ CFU/ml regardless of the bacterial inoculation level, and even at the 70:1 inoculation ratio, glucose, ethanol, and lactic acid concentrations did not change from the steady-state concentrations seen before bacterial inoculation. However, L. paracasei decreased steadily from its initial inoculation level of ∼2.2×10⁹ CFU/ml and stabilized at 3.7×10⁵ CFU/ml after 10 days of steady-state operation. Both organisms then persisted in the multistage system at an approximate L. paracasei/S. cerevisiae ratio of 1:100 which confirms that, in continuous fuel ethanol production, it would be difficult to eliminate this bacterium. Only when the pH was controlled at 6.0 in fermentor 1 (F1) were changes seen which would affect the multistage system. Ethanol concentration then decreased by 44% after 4 days of pH-controlled operation. This coincided with an increase in L. paracasei to >10¹⁰ CFU/ml, and a 4× increase in lactic acid concentration to 20 g/l. When the clarified contents from other fermentors (F2–F5) in the multistage system were used as growth media, L. paracasei was not able to grow in batch culture. This indicated that the first fermentor in the multistage system was the only fermentor capable of supporting the growth of L. paracasei under the described conditions. Journal of Industrial Microbiology & Biotechnology (2001) 27, 39–45. Received 26 February 2001/ Accepted in revised form 29 May 2001     

副干酪乳杆菌PC-01全基因组测序及不同副干酪乳杆菌菌株比较基因组学分析

【背景】副干酪乳杆菌(Lactobacillus paracasei)作为乳酸菌中重要菌种之一,常被认为是优良益生菌开发的潜在资源。【目的】以L.paracasei PC-01和L.paracasei Zhang为例,分析不同L.paracasei的基因组差异和遗传背景,为菌株的鉴定和开发奠定基础。【方法】采用PacBioSMRT三代测序技术对L.paracasei PC-01进行全基因组测序,结合2株L.paracasei模式菌株和公开的36株全基因组数据,通过比较基因组学方法揭示39株L.paracasei菌株之间的差异。【结果】L.paracasei PC-01基因组不包含质粒,染色体大小为2 829 251 bp,GC含量为46.64%;L.paracasei Zhang包含一个质粒基因组大小为2 898 456 bp,GC含量为46.51%;不同L.paracasei菌株基因组大小、质粒数及GC含量均存在一定差异。L.paracasei群体为开放式基因组,基因组具有高度多样性。基于核心基因构建系统发育树对于L.paracasei种内区分效果最好,L.paracasei PC-01和L.paracasei Zhang处于不同的进化分支。约占L.paracasei PC-01基因组长度91%的片段与L.paracasei Zhang基因组匹配率大于90%,L.paracasei PC-01注释到10个与转录调节鼠李糖代谢功能相关的特有基因,如agu A、clp B等;L.paracasei Zhang包含msh A、ltr A等特有基因,与糖基转移等功能相关。【结论】通过比较基因组学揭示L.paracasei PC-01和L.paracasei Zhang的遗传信息,解析了不同L.paracasei菌株之间的差异,为L.paracasei的鉴定和应用奠定了遗传学基础。     

Changes in lactic acid bacteria and components of Awa-bancha by anaerobic fermentation

ABSTRACT

Awa-bancha is a post-fermented tea produced in Naka and Kamikatsu, Tokushima, Japan. We investigated the lactic acid bacteria in each stage of production of Awa-bancha and evaluated the relationships with the components. Lactic acid bacteria were isolated from tea leaves cultured with de Man, Rogosa, and Sharpe (MRS) agar plates, and the species were identified by homology of the 16 S rRNA gene and multiplex polymerase chain reaction (PCR) of the recA gene to distinguish the Lactobacillus plantarum group. As a result, a variety of species were isolated from the raw tea leaves, and Lactobacillus pentosus was isolated most frequently after anaerobic fermentation. Regarding the tea leaf components, organic acids, such as lactic acid, increased, free amino acids decreased, and catechins changed owing to anaerobic fermentation. Our results suggest that the microbial flora mainly composed of L. pentosus is important in the anaerobic fermentation process for flavor formation of Awa-bancha.     

Bactericidal and non-cytotoxic activity of bacteriocin produced by Lacticaseibacillus paracasei F9-02 and evaluation of its tolerance to various physico-chemical conditions

This study aims to explore novel lactic acid bacteria (LAB) from breast-fed infants' faeces towards characterizing their antimicrobial compound, bacteriocin. The LAB, Lacticaseibacillus paracasei F9-02 showed strong antimicrobial activity against clinical pathogens. Their proteinaceous nature was confirmed as the activity was completely abolished when treated with proteinaceous enzymes and retained during neutral pH and catalase treatment. The purified bacteriocin showed antimicrobial activity at the minimum inhibitory concentration (MIC) value of 7.56 μg/ml against vancomycin-resistant Enterococcus sp. [vancomycin-resistant enterococcal (VRE)], and methicillin-resistant Staphylococcus aureus (MRSA), 15.13 μg/ml against Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica serotype typhi and 30.25 μg/ml against Shigella flexneri. Present study also proved the bactericidal, non-cytotoxic and non-hemolytic nature of bacteriocin. Additionally, bacteriocin retained their stability under various physico-chemical conditions, broad range of pH (2–10), temperature (40–121°C), enzymes (amylase, lipase and lysozyme), surfactants [Tween-20, 80, 100 and sodium dodecyl sulfate (SDS)], metal ions (CaCl₂, FeSO₄, ZnSO₄, MgSO₄, MnSO₄, CuCl₂) and NaCl (2%–8%). The molecular weight of bacteriocin (~28 kDa) was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), functional and active groups were assessed by Fourier Transform-Infrared (FT-IR). To our knowledge, this is the first study reporting L. paracasei from breast-fed infants' faeces and assessing their antimicrobial compound, bacteriocin. The study results furnish the essential features to confirm the therapeutic potential of L. paracasei F9-02 bacteriocin.     

The effect of Lactobacillus buchneri on the fermentation, aerobic stability and ruminal degradability of maize silage

AIMS: To evaluate the effect of Lactobacillus buchneri, heterofermentative lactic acid bacteria (LAB), on the fermentation, aerobic stability and ruminal degradability of whole-crop maize silages under laboratory conditions. Two homofermentative LAB were tested for the purpose of comparison. METHODS AND RESULTS: Maize was harvested at early dent [290 g kg(-1) dry matter (DM)] and one-half milk line (355 g kg(-1) DM) stages. Both homofermentative LAB were applied at 1 x 10(5) CFU g(-1) of fresh forage. Lactobacillus buchneri was applied at 1 x 10(5), 5 x 10(5) and 1 x 10(6) CFU g(-1) of fresh forage. Silages with no additives served as control. After treatment, the chopped forages were ensiled in 1.5-l anaerobic jars. Three jars per treatment were sampled on day 60. After 60 days of storage, silages were subjected to an aerobic stability test lasting for 5 days, in which CO(2) production, as well as chemical and microbiological parameters, was measured to determine the extent of aerobic deterioration. Both homofermentative LAB increased the concentration of lactic acid and the numbers of yeasts, and decreased the concentration of acetic acid and impaired the aerobic stability of silages. In contrast, applying L. buchneri decreased the concentration of lactic acid and increased the concentration of acetic acid of the silages. Under aerobic conditions, silages treated with 5 x 10(5) and 1 x 10(6) CFU g(-1) of L. buchneri, had lower pH, CO(2) production and the numbers of yeasts than the silages treated with 1 x 10(5) CFU g(-1) of L. buchneri (P < 0.05). However, all doses of L. buchneri and both homofermentative LAB did not affect in situ rumen DM, organic matter and neutral detergent fibre degradability of the silages. CONCLUSIONS: Lactobacillus buchneri was very effective in protecting maize silages exposed to air under laboratory conditions. All doses of L. buchneri, especially 5 x 10(5) CFU g(-1) or more, markedly decreased the numbers of yeasts and improved the aerobic stability of silages. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of L. buchneri, as a silage inoculant, can improve the aerobic stability of maize silages by inhibition of yeast activity.     

Lactobacillus pentosus CECT 4023 T co-utilizes glucose and xylose to produce lactic acid from wheat straw hydrolysate: Anaerobiosis as a key factor

Lactic acid is a versatile chemical that can be produced via fermentation of lignocellulosic materials. The heterolactic strain Lactobacillus pentosus CECT 4023 T, that can consume glucose and xylose, was studied to produce lactic acid from steam exploded wheat straw prehydrolysate. The effect of temperature and pH on bacterial growth was analyzed. Besides, the effect of oxygen on lactic acid production was tested and fermentation yields were compared in different scenarios. This strain showed very high tolerance to the inhibitors contained in the wheat straw prehydrolysate. The highest lactic acid yields based on present sugar, around 0.80 g g⁻¹, were obtained from glucose in presence of 25%, 50%, and 75% v v⁻¹ of prehydrolysate in strict anaerobiosis. Lactic fermentation of wheat straw hydrolysate obtained after enzymatic hydrolysis of the prehydrolysate yielded 0.39 g of lactic acid per gram of released sugars, which demonstrated the high potential of L. pentosus to produce lactic acid from hemicellulosic hydrolysates. Results presented herein not only corroborated the ability of L. pentosus to grow using mixtures of sugars, but also demonstrated the suitability of this strain to be applied as an efficient lactic acid producer in a lignocellulosic biorefinery approach. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2739, 2019     

High-Level Expression of Heme-Dependent Catalase Gene <Emphasis Type="Italic">katA</Emphasis> from <Emphasis Type="Italic">Lactobacillus Sakei</Emphasis> Protects <Emphasis Type="Italic">Lactobacillus Rhamnosus</Emphasis> from Oxidative Stress

Lactic acid bacteria (LAB) are generally sensitive to hydrogen peroxide (H₂O₂), Lactobacillus sakei YSI8 is one of the very few LAB strains able to degrade H₂O₂ through the action of a heme-dependent catalase. Lactobacillus rhamnosus strains are very important probiotic starter cultures in meat product fermentation, but they are deficient in catalase. In this study, the effect of heterologous expression of L. sakei catalase gene katA in L. rhamnosus on its oxidative stress resistance was tested. The recombinant L. rhamnosus AS 1.2466 was able to decompose H₂O₂ and the catalase activity reached 2.85 μmol H₂O₂/min/10⁸ c.f.u. Furthermore, the expression of the katA gene in L. rhamnosus conferred enhanced oxidative resistance on the host. The survival ratios after short-term H₂O₂ challenge were increased 600 and 10⁴-fold at exponential and stationary phase, respectively. Further, viable cells were 100-fold higher in long-term aerated cultures. Simulation experiment demonstrated that both growth and catalase activity of recombinant L. rhamnosus displayed high stability under environmental conditions similar to those encountered during sausage fermentation.     

Identification and characterization of yeasts in sugarcane silages

Aims: To enumerate the micro‐organisms and to identify the yeast species present during the ensilage of different sugarcane (Saccharum spp.) cultivars. Method: Samples of sugarcane silage were collected at 10, 20, 30 and 40 days from the start of fermentation. Population levels of lactic acid bacteria (LAB), mesophilic facultative anaerobic (MFA) bacteria, filamentous fungi and yeasts were determined. Nine species of yeasts were classified according to traditional methods and confirmed using molecular techniques. Conclusions: LAB dominated the ensiling process of sugarcane, although yeasts were present at relatively high population levels throughout the whole fermentation period. The detected species of yeasts varied according to sugarcane cultivar and time of fermentation. Torulaspora delbrueckii was the predominant yeast, followed by Pichia anomala and Saccharomyces cerevisiae. Significance and Impact of the Study: Knowledge of the population of micro‐organisms in general, and of yeasts in particular, present during the fermentation of sugarcane is of fundamental importance in the development of more effective ensiling processes.