Optimization of gluconic acid synthesis by removing limitations and inhibitions

The optimization task was performed using the gluconic acid synthesis by the Acetobacter methanolicusMB 58 strain. The microorganisms were grown continuously on methanol as the growth substrate. After finishing the growth process by the deficiency of N and P, the gluconic acid synthesis was started by adding glucose. The synthesis process was performed continuously. The oxygen transfer rate depended on the gluconic acid concentration. During the growth process, the oxygen transfer rate reached a value of about 13 g O₂ · kg^?1 · h^?1using a 30-l glass fermenter equipped with a 6 blade stirrer and fully baffled. This rate declined to a value of between 2 and 5 g O₂ · kg^?1 · h^?1 in the presence of gluconic acid concentrations above 150 g gluconic acid · kg^?1medium. The yield (g gluconic acid · g^?1glucose) depended on the gluconic acid concentration and amounted to y = 0.7 in relation to 150 g gluconic acid · kg^?1medium and y = 0.8 in relation to 200 g · kg^?1medium, respectively. The fermenters were coupled with ultrafiltration moduls (Fa. ROMICON and Fa. SARTORIUS). The biomass concentrations amounted from 5 to 40 g dry mass kg^?1medium. The ultrafiltration modules retained the biomass within the fermentation system. A glucose solution (30 to 50 weight percent glucose) was continuously dosed into the fermenter. The retention time was chosen between 2 and 30 h. The gluconic acid synthesis rate reached values of up to 32 g gluconic acid · kg^?1 · h^?1. Within a range of up to 250 g gluconic acid · kg^?1medium, the acid concentration had no influence on the enzyme activity.     

Isolation,Selection and Characterization of Root-Associated Rock Phosphate Solubilizing Bacteria in Moroccan Wheat (Triticum aestivum L.)

Abstract

Phosphorus (P) is the most important macronutrient next to nitrogen for the growth and development of plants. But often unavailable for plants because of its high reactivity with many soil constituents. Thus, the use of phosphate solubilizing bacteria (PSBs) as biofertilizers seems to be an effective way to resolve the soluble phosphorus availability in soil. The present study was conducted to isolate and characterize rock PSB associated with the rhizosphere of wheat (Triticum aestivum L.) from fourteen different wheat-growing sites of Meknes region in Morocco. A total of one hundred ninety-eight (198) rock PSBs were isolated employing NBRIP medium amended with rock phosphate (RP), out of which five strains (A17, A81, B26, B106, and B107) were selected for their strong ability to dissolve RP and were tested in vitro for plant growth-promoting (PGP) traits including production of indole acetic acid (IAA), siderophores, hydrogen cyanide (HCN), and antifungal activity, as well as their response to the effect of extrinsic and intrinsic stress. The 16S rRNA gene sequencing and phylogenetic analysis identified these isolates belong to four genera, Pantoea, Pseudomonas, Serratia, and Enterobacter. The phosphate solubilization index (SI) of selected isolates ranged between 2.3 and 2.7, and the amount of solubilized phosphorus in the liquid medium varied from 59.1 to 90.2 µg mL^?1. HPLC analysis revealed that all the selected isolates produced multiple organic acids (oxalic, citric, gluconic succinic, and fumaric acids) from glucose under aerobic conditions. Except for the A81 strain, all selected isolates were able to produce IAA ranging between 2.9 and 21.2 µg mL^?1. The isolates A17, B26, and B107 showed the ability to produce siderophores ranging from 79.3 to 20.8% siderophore units. Only two strains (A17 and B26) were able to produce HCN. All selected isolates showed good resistance against different environmental stresses like 10–50?°C temperature, 0.5–2?g L^?1 salt concentration and 4.5–9?pH range, and against different antibiotics. The antagonistic effect showed that among the five selected strains, only two strains (B26 and A17) were able to suppress the growth of tested fungi. This study clearly indicates that our selected rock PSBs can be used as biofertilizers for grain crops after studying their interaction with the host crop and field evaluation.     

Determination of glucose-fructose oxidoreductase activity in whole cells of Zymomonas mobilis

A method for the determination of glucose-fructose oxidoreductase (GFOR) activity in whole cells of Zymomonas mobilis is described. The K _m and the theoretical V _max for GFOR were 192 g glucose.l^-1 and 17 g gluconic acid.g^-1 cell.h^-1, respectively. The changes in enthalpy (31.1 kJ.mol^-1), entropy (0.41 kJ.K^-1), and Gibbs free energy (-97.5 kJ.mol^-1) related to glucose to gluconic acid conversion were also determined.     

Pseudomonas azotoformans F77和Pseudomonas paracarnis P1风化黑云母的效应及机制比较

【目的】比较高效矿物风化固氮假单胞菌(Pseudomonas azotoformans) F77及其亲缘关系较近的假单胞菌(Pseudomonas paracarnis) P1风化黑云母的效应和机制。【方法】通过检测两株菌在不同时间点的发酵液中细胞数量、pH值、葡萄糖剩余量、葡萄糖酸浓度和可溶性Fe、Al释放量,比较它们对黑云母的风化效果与生理机制。采用RNA-seq技术研究这两株菌风化黑云母过程中出现差异的分子机制。【结果】在持续5 d的风化试验中,菌株F77发酵液中的细胞数量和pH值低于菌株P1,葡萄糖酸浓度是菌株P1的27.3-53.9倍,Fe和Al元素的释放量是菌株P1的3.3-23.3倍。比较转录组数据表明,菌株F77特有的基因数量(2 872)和差异基因数量(1 832)均多于菌株P1 (分别为1 903和1 258)。菌株F77在胞内物质跨膜转运与碳代谢、细胞运动、趋化与信号诱导等途径中基因数量也高于菌株P1。此外,菌株F77的超氧化物歧化酶和过氧化氢酶基因差异表达倍数、葡萄糖酸合成基因数量和差异表达倍数也明显高于菌株P1。【结论】菌株F77风化黑云母以及合成葡萄糖酸的能力显著高于菌株P1。菌株F77通过产生葡萄糖酸来促进黑云母的风化。添加黑云母显著促进了菌株F77胞内与矿物风化相关基因的表达,如物质跨膜转运、细胞运动与趋化、信号诱导、碳代谢及能量代谢等途径基因。此外,葡萄糖酸合成途径基因、超氧化物歧化酶基因以及过氧化氢酶基因在矿物风化中可能发挥重要作用。     

Variations in carbon-to-phosphorus ratios of two Australian strains of Cylindrospermopsis raciborskii

The toxic cyanobacterium Cylindrospermopsis raciborskii can form large blooms in freshwater systems, causing water quality problems. The availability of the essential macronutrient phosphorus (P), has a big impact on bloom formation but the variation in physiological response of different strains of C. raciborskii to available P has not previously been examined. This study investigated the carbon:phosphorus (C:P) ratio of two toxic Australian strains of C. raciborskii, AWT205 and NPD, under a range of P concentrations in batch and continuous cultures. P was added as a single dose to batch cultures and in continuous cultures at P concentrations of 0.032, 0.16, 0.64 and 16 μmol P l^?1. Cellular carbon and phosphorus content of both strains increased under P-limited conditions (0 μmol P l^?1 addition) with zero growth. Strain NPD had a lower C:P ratio (34:1) than AWT205 (150:1) indicating higher P storage capacity, and strain NPD survived P-limited conditions for longer. There was no significant difference in exponential growth rates (0.2 d^?1, P ≥ 0.5) under all P concentrations for both strains, with the exception of no P, demonstrating non-P-limited growth even at the lowest concentration (0.032 µmol P l^?1) and no increase in growth rate with additional P. ³³P uptake measurements were used to show that these strains both have very low half saturation constants (K_s = 0.02 μmol P l^?1) compared with other phytoplankton and strains of C. raciborskii. This is indicative of high uptake affinities and suggests that these strains are highly adapted to a low P supply. Overall the results of this study are consistent with the P strategy of storage prioritization over growth rate, and demonstrate differences between the strains in the C:P ratio under P-limitation, indicating variation in P storage.     

Optimization of erythritol production by Candida magnoliae in fed-batch culture

A two-stage fed-batch process was designed to enhance erythritol productivity by the mutant strain of Candida magnoliae. The first stage (or growth stage) was performed in the fed-batch mode where the growth medium was fed when the pH of the culture broth dropped below 4.5. The second stage (or production stage) was started with addition of glucose powder into the culture broth when the cell mass reached about 75 g dry cell weight l⁻¹. When the initial glucose concentration was adjusted to 400 g l⁻¹ in the production stage, 2.8 g l⁻¹ h⁻¹ of overall erythritol productivity and 41% of erythritol conversion yield were achieved, which represented a fivefold increase in erythritol productivity compared with the simple batch fermentation process. A high glucose concentration in the production phase resulted in formation of organic acids including citrate and butyrate. An increase in dissolved oxygen level caused formation of gluconic acid instead of citric acid. Journal of Industrial Microbiology & Biotechnology (2000) 25, 100–103. Received 25 February 2000/ Accepted in revised form 08 June 2000     

Characterization of the Mineral Phosphate-Solubilizing Activity of <Emphasis Type="Italic">Pantoea aglomerans</Emphasis> MMB051 Isolated from an Iron-Rich Soil in Southeastern Venezuela (Bolívar State)

The mineral phosphate-solubilizing (MPS) activity of a Pantoea agglomerans strain, namely MMB051, isolated from an iron-rich, acidic soil near Ciudad Piar (Bolívar State, Venezuela), was characterized on a chemically defined medium (NBRIP). Various insoluble inorganic phosphates, including tri-calcium phosphate [Ca₃(PO₄)₂], iron phosphate (FePO₄), aluminum phosphate (AlPO₄), and Rock Phosphate (RP) were tested as sole sources of P for bacterial growth. Solubilization of Ca₃(PO₄)₂ was very efficient and depended on acidification of the external milieu when MMB051 cells were grown in the presence of glucose. This was also the case when RP was used as the sole P source. On the other hand, the solubilization efficiency toward more insoluble mineral phosphates (FePO₄ and AlPO₄) was shown to be very low. Even though gluconic acid (GA) was detected on culture supernatants of strain MMB051, a consequence of the direct oxidation pathway of glucose, inorganic-P solubilization seemed also to be related to other processes dependent on active cell growth. Among these, proton release by ammonium (NH₄⁺) fixation appeared to be of paramount importance to explain inorganic-P solubilization mediated by strain MMB051. On the contrary, the presence of nitrate (NO₃^–) salts as the sole N source affected negatively the ability of MMB051 cells to solubilize inorganic P.     

Characterization of the mineral phosphate solubilizing activity of <Emphasis Type="Italic">Serratia marcescens</Emphasis> CTM 50650 isolated from the phosphate mine of Gafsa

The mineral phosphate solubilizing (MPS) ability of a Serratia marcescens strain, namely CTM 50650, isolated from the phosphate mine of Gafsa, was characterized on a chemically defined medium (NBRIP broth). Various insoluble inorganic phosphates, including rock phosphate (RP), calcium phosphate (CaHPO₄), tri-calcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite were tested as sole sources of phosphate for bacterial growth. Solubilization of these phosphates by S. marcescens CTM 50650 was very efficient. Indeed, under optimal conditions, the soluble phosphorus (P) concentration it produced reached 967, 500, 595 and 326 mg/l from CaHPO₄, Ca₃(PO₄)₂, hydroxyapatite and RP, respectively. Study of the mechanisms involved in the MPS activity of CTM 50650, showed that phosphate solubilization was concomitant with significant drop in pH. HPLC-analysis of culture supernatants revealed the secretion of gluconic acid (GA) resulting from direct oxidation pathway of glucose when the CTM 50650 cells were grown on NBRIP containing glucose as unique carbon source. This was correlated with the simultaneous detection by PCR for the first time in a S. marcescens strain producing GA, of a gene encoding glucose dehydrogenase responsible for GA production, as well as the genes pqqA, B, C and E involved in biosynthesis of its PQQ cofactor. This study is expected to lead to the development of an environmental-friendly process for fertilizer production considering the capacity of S. marcescens CTM 50650 to achieve yields of P extraction up to 75% from the Gafsa RP.     

Rapid solubilization of insoluble phosphate by a novel environmental stress-tolerant Burkholderia vietnamiensis M6 isolated from ginseng rhizospheric soil

We isolated and characterized novel insoluble phosphate (P)-solubilizing bacteria tolerant to environmental factors like high salt, low and high pHs, and low temperature. A bacterium M6 was isolated from a ginseng rhizospheric soil and confirmed to belong to Burkholderia vietnamiensis by BIOLOG system and 16S rRNA gene analysis. The optimal cultural conditions for the solubilization of P were 2.5% (w/v) glucose, 0.015% (w/v) urea, and 0.4% (w/v) MgCl₂·6H₂O along with initial pH 7.0 at 35°C. High-performance liquid chromatography analysis showed that B. vietnamiensis M6 produced gluconic and 2-ketogluconic acids. During the culture, the pH was reduced with increase in gluconic acid concentration and was inversely correlated with P solubilization. Insoluble P solubilization in the optimal medium was about 902 mg l⁻¹, which was approximately 1.6-fold higher than the yield in NBRIP medium (580 mg l⁻¹). B. vietnamiensis M6 showed resistance against different environmental stresses like 10–45°C, 1–5% (w/v) salt, and 2–11 pH range. The maximal concentration of soluble P produced by B. vietnamiensis M6 from Ca₃(PO₄)₂, CaHPO₄, and hydroxyapatite was 1,039, 2,132, and 1,754 mg l⁻¹, respectively. However, the strain M6 produced soluble P with 20 mg l⁻¹ from FePO₄ after 2 days and 100 mg l⁻¹ from AlPO₄ after 6 days, respectively. Our results indicate that B. vietnamiensis M6 could be a potential candidate for the development of biofertilizer applicable to environmentally stressed soil.     

Effects of temperature, and availability of nitrogen and phosphorus on the abundance of Anabaena and Microcystis in Lake Biwa, Japan: an experimental approach

Under optimal nutrient conditions, both Microcystis sp. and Anabaena sp. isolated from Lake Biwa grew optimally at 28–32°C but differed in maximal growth rates, phosphate uptake kinetics, maximal phosphorus quotas, and growth responses to nitrogen and phosphorus limitation. The maximal growth rates of Microcystis and Anabaena were 1.6 and 1.25 divisions day⁻¹, respectively. With phosphate and nitrate in the growth-limiting range, the growth of Microcystis was optimal at an N : P ratio of 100 : 1 (by weight) and declined at lower (nitrogen limitation) and higher (phosphorus limitation) ratios. In contrast, Anabaena growth rates did not change at N : P ratios from 1000 : 1 to 10 : 1. Starting with cells containing the maximal phosphorus quota, Microcystis growth in minus-phosphorus medium ceased in 7–9 days, compared with 12–13 days for Anabaena. The phosphate turnover time in cultures starved to their minimum cell quotas was 7.9 min for Microcystis and 0.6 min for Anabaena. Microcystis had a higher K _s (0.12 μg P l⁻¹ 10⁻⁶ cells) and lower V _max (9.63 μg P l⁻¹ h⁻¹ 10⁻⁶ cells), than Anabaena (K _s 0.02 μg P l⁻¹ h⁻¹ 10⁻⁶ cells; V _max 46.25 63 μg P l⁻¹ h⁻¹ 10⁻⁶ cells), suggesting that Microcystis would not be able to grow well in phosphorus-limited waters. We conclude that in spite of the higher growth rate under ideal conditions, Microcystis does not usually bloom in the North Basin because of low availability of phosphorus and nitrogen. Although Anabaena has an efficient phosphorus-uptake system, its main strategy for growth in low-phosphorus environments may depend on storage of phosphorus during periods of abundant phosphorus supply, which are rare in the North Basin. Received: July 31, 2000 / Accepted: October 18, 2000     

Organic acid production and plant growth promotion as a function of phosphate solubilization by Acinetobacter rhizosphaerae strain BIHB 723 isolated from the cold deserts of the trans-Himalayas

An efficient phosphate-solubilizing plant growth–promoting Acinetobacter rhizosphaerae strain BIHB 723 exhibited significantly higher solubilization of tricalcium phosphate (TCP) than Udaipur rock phosphate (URP), Mussoorie rock phosphate (MRP) and North Carolina rock phosphate (NCRP). Qualitative and quantitative differences were discerned in the gluconic, oxalic, 2-keto gluconic, lactic, malic and formic acids during the solubilization of various inorganic phosphates by the strain. Gluconic acid was the main organic acid produced during phosphate solubilization. Formic acid production was restricted to TCP solubilization and oxalic acid production to the solubilization of MRP, URP and NCRP. A significant increase in plant height, shoot fresh weight, shoot dry weight, root length, root dry weight, and root, shoot and soil phosphorus (P) contents was recorded with the inoculated treatments over the uninoculated NP₀K or NP_TCPK treatments. Plant growth promotion as a function of phosphate solubilization suggested that the use of bacterial strain would be a beneficial addition to the agriculture practices in TCP-rich soils in reducing the application of phosphatic fertilizers.     

Influence of pH,lactose and lactic acid on the growth of Streptococcus cremoris: a kinetic study

Summary The effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l^-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l^-1 demonstrated. With the product yield of 0.9 g·g^-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l^-1 could not explain the low growth rates obtained, implicating a nutritional limitation.Symbols t _f fermentation duration (h) - X Biomass concentration (g·l^-1) - X _m maximum biomass concentration (g·l^-1) - S lactose concentration (g·l^-1) - S _r residual lactose concentration (g·l^-1) - P produced lactic acid concentration (g·l^-1) - P _a added lactic acid concentration (g·l^-1) - P _c critical lactic acid concentration (g·l^-1) - specific growth rate (h^-1) - _max maximum specific growth rate (h^-1) - R _x/S biomass yield (g·g^-1) calculated when =0 - R _P/S product yield (g·g^-1)     

Development of a microtitre plate method for determination of phenol utilization, biofilm formation and respiratory activity by environmental bacterial isolates

Twenty-five aerobic phenol-degrading bacteria, isolated from different environmental samples on phenol agar after several subcultures in phenol broth, utilized phenol (0.2 g l⁻¹) within 24 h, but removal of phenol was more rapid when other carbon sources were also present. A microtitre plate method was developed to determine growth rate, biofilm formation and respiratory activity of the strains isolated. Pseudomonas putida strains C5 and D6 showed maximum growth (as O.D. at 600 nm), P. putida D6 and unidentified bacterial strain M1 were more stable at high concentrations of phenol (0.8 g l⁻¹), and P. putida C5 formed the greatest amount of biofilm in 0.5 g phenol l⁻¹ medium. Measurement of dehydrogenase activity as reduction of triphenyl tetrazolium chloride supported data on growth rate and biofilm formation. The microtitre plate method provided a selective method for detection of the best phenol degrading and biofilm-forming microorganisms, and was also a rapid, convenient means of studying the effect of phenol concentration on growth rate and biofilm formation.     

Effect of biotic and abiotic elicitors on production of betulin and betulinic acid in the hairy root culture of Betula pendula Roth

Abstract

Betulin (B) and betulinic acid (BA) are two triterpenoids with a wide range of biological and medicinal activities in different organs of Betula pendula. This research aimed to increase the accumulation of B and BA in the hairy root culture of B. pendula by seven biotic and abiotic elicitors. Hairy root was induced in the stem’s inner bark of B. pendula using the C58C1 strain in the WPM (Woody Plant Medium). The effects of different concentrations of elicitors and different time of root harvest in hairy root culture of B. pendula showed that highest level of growth index (GI), B, and BA was acquired in treated hairy roots with chitosan (CTS), chlorocholine chloride (CCC) and chitosan nano-fiber (CTS NF). Highest GI of B. pendula hairy roots was 13 that was obtained in the roots treated with CTS 150?mg l^?1 on the 8th day. The highest content of BA was 1.3?mg g^?1 DW after treatment with 1?mg l^?1CCC on the 4th and 6th days and 200?mg l^?1CTS NF on the 10th day. The highest B content (0.94?mg g^?1DW) was obtained in the treated hairy root by 2?mg l^?1 CCC after 4 and 6?days.     

Homofermentative production of d-lactic acid from sucrose by a metabolically engineered Escherichia coli

Escherichia coli W, a sucrose-positive strain, was engineered for the homofermentative production of d-lactic acid through chromosomal deletion of the competing fermentative pathway genes (adhE, frdABCD, pta, pflB, aldA) and the repressor gene (cscR) of the sucrose operon, and metabolic evolution for improved anaerobic cell growth. The resulting strain, HBUT-D, efficiently fermented 100?g?sucrose?l^?1 into 85?g?d-lactic acid?l^?1 in 72–84?h in mineral salts medium with a volumetric productivity of ~1?g?l^?1?h^?1, a product yield of 85?% and d-lactic acid optical purity of 98.3?%, and with a minor by-product of 4?g?acetate?l^?1. HBUT-D thus has great potential for production of d-lactic acid using an inexpensive substrate, such as sugar cane and/or beet molasses, which are primarily composed of sucrose.     

Optimization of the growth parameters of Aspergillus foetidus

The batch production of gluconic acid in the presence of glucose, sucrose and molasses was investigated using free mycelia of Aspergillus foetidus NRRL 337 in shake flasks. Eight growth parameters were chosen as independent variables. The temperature, pH, substrate type and initial concentrations, inoculum percentage and shake rate directly affected the specific microorganism growth and gluconic acid production rates. The optimum temperature and initial pH values were found to be 33°C and five to six, respectively. The maximum specific growth and gluconic acid production rates were established as 57 g/dm³ of glucose, 75 g/dm³ of sucrose and 150 g/dm³ of molasses. The optimum values of the shake rate, inoculum percentage and initial ammonium nitrate concentration were determined as 100 1/min, 0.5% and 1.5 g/dm³, respectively. The maximum gluconic acid concentrations corresponding to these initial substrate concentrations were observed to be 8.3 g/dm³, 17.4 g/dm³ 37.0 g/dm³, respectively. The optimum specific microbial growth and gluconic acid production rates were found as 0.0145 1/h and 0.0375 g/g × h, respectively, for the fermentation conditions of S_Go = 57 g/dm³, T = 28°C, initial pH = 6.5, N = 84 1/min, A = 0.5 g/dm³ and I = 0.5%.     

Biological acidification during grape must fermentation using mixed cultures of <Emphasis Type="Italic">Kluyveromyces thermotolerans</Emphasis> and <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Four mixed culture fermentations of grape must were carried out with Kluyveromyces thermotolerans strain TH941 and Saccharomyces cerevisiae strain SCM952. In the first culture, both yeasts were added together, whereas in the remaining three cultures S. cerevisiae was added 1, 2, and 3 days after the inoculation of K. thermotolerans. The growth and survival of the K. thermotolerans strain and the amount of the produced l-lactic acid depend on the time of inoculation of the S. cerevisiae strain and provided an effective acidification during alcoholic fermentation. The four cultures contained, respectively, at the end of fermentation 0.18, 1.80, 4.28, and 5.13 g l-lactic acid l⁻¹. The grape must with an initial pH of 3.50 was effectively acidified (70% increase in titratable acidity, 0.30 pH unit decrease) by the production of 5.13 g l-lactic acid l⁻¹.     

Production of gluconic acid by immobilized in pumice stones mycelium of Aspergillus niger using unconventional oxygenation of culture

Gluconic acid was produced in repeated batch processes with Aspergillus niger AM-11, immobilized in pumice stone particles using an unconventional oxygenation of culture media based on the addition of H₂O₂, decomposed by catalase to O₂ and water. The highest gluconic acid productivity of 8.2 g l^–1 h^–1 was reached with 30 g immobilized mycelium per 150 ml, 10% (w/v) glucose, at 24 °C and pH 6.5, with O₂ at 100% saturation. The immobilized mycelium was successfully reused up to 8 times in 1-h batches with only a slight loss (11%) of gluconic acid productivity.     

Control of green mould of citrus by using Trichoderma harzianum,humic acid or garlic

Penicillium digitatum, an aggressive fungus causes post-harvest decay of mandarin sweet orange and Washington navel. In vitro Trichoderma harzianum or humic acid (HA) or powdered cloves of garlic caused inhibition of fungal growth of isolates P₁ and P₂. Under storage conditions, the fruit citrus is protected by using T. harzianum with standard volume 2.0?ml (9.6?×?10⁶?conidia/ml) and application 24?h before inoculation reduces disease incidence and disease severity after seven?days from inoculation with P. digitatum spore suspension (1.0?×?10⁶?spores/ml) compared to control. Spraying the fruit citrus by standard volume of 2.0?ml of either HA or powder cloves of garlic 1% on each fruit 24?h before inoculation reduces disease incidence and disease severity after seven?days from inoculation with P. digitatum (1.0?×?10⁶ spores/ml) compared to control. The lowest percentage of disease incidence and disease severity were associated with powder of cloves garlic and followed by HA and T. harzianum during two growing seasons compared with the untreated and control.     

Effect of oxygen on batch yogurt cultures

A yogurt culture (Streptococcus thermophilus 15HA + Lactobacillus delbrueckii subsp. bulgaricus 2-11) was studied in conditions of aerobic batch fermentation (10–40% dissolved oxygen in milk). The growth and acidification of S. thermophilus 15HA were stimulated at 20% oxygen concentration and the lactic acid process in a mixed culture was shortened by 1 h (2.5 h for the aerobic culture and 3.5 h for the anaerobic mixed culture). Streptococcus thermophilus 15HA oxygen tolerance was significantly impaired at oxygen concentrations in the milk above 30%. Though S. thermophilus 15HA was able to overcome to some extent the impact of high oxygen concentration (40%), the lactic acid produced was insufficient to coagulate the milk casein (4.0 g lactic acid l⁻¹ in the mixed culture and 3.8 g lactic acid l⁻¹ in the pure culture). A dramatic decrease in the viable cell count of L. delbrueckii subsp. bulgaricus 2-11 in the pure and mixed cultures was recorded at 30% dissolved oxygen. This revised version was published online in July 2006 with corrections to the Cover Date.