Oxygen uptake rate regulation during cell growth phase for improving avermectin B<Subscript>1a</Subscript> batch fermentation on a pilot scale (2 m<Superscript>3</Superscript>)

Avermectin B_1a batch fermentation of Streptomyces avermitilis in a 2 m³ fermentor was investigated by oxygen uptake rate (OUR) regulation during cell growth phase. OUR was controlled by adjusting of aeration and agitation. Result showed that OUR strongly affected cell growth and antibiotics production. Avermectin B_1a biosynthesis could be effectively enhanced when OUR was stably regulated at an appropriate level in batch fermentation of S. avermitilis. Avermectin B_1a yield reached 5568 ± 111 mg/l by controlling maximal OUR between 15 and 20 mmol/l/h during cell growth phase, which was increased by 21.8% compared with the control (maximal OUR above 20 mmol/l/h). The stimulation effect on avermectin B_1a production could be attributed to the improved supply of propionic acid and acetic acid, the precursors of avermectin B_1a, in the cells. Hence, this OUR control method during cell growth phase may be a simple and applicable way to improve industrial production of avermectin.     

Analysis of neutral lipid biosynthesis in Streptomyces avermitilis MA-4680 and characterization of an acyltransferase involved herein

The physiology of lipid production in Streptomyces avermitilis MA-4680 with regard to the fatty acid composition of the accumulated lipids and their cellular distribution was analyzed. Cells were able to accumulate about ten to 30 lipid granules with diameters between 100 and 500 nm filling about 70–80% of the cell cytoplasm. Gas chromatography/mass spectrometry analyses of total cellular lipids and from isolated triacylglycerols (TAG) confirmed a similar fatty acid composition with a large portion of iso- and anteiso-methyl-branched fatty acids. De novo biosynthesis of wax esters (WE) appeared only during cocultivation on glucose and hexadecanol as carbon source. Homology alignments with the wax ester synthase/acyl-CoA:diacylglycerol acyltransferase (WS/DGAT; AtfA) from Acinetobacter baylyi strain ADP1 yielded one open reading frame in the genome databases of S. avermitilis MA-4680 referred to as SAV7256 with 25.3% homology. The highly conserved HHAxxDG active site motif found in AtfA, which is present in SAV7256, as well as the similar hydrophobicity profiles of AtfA and SAV7256 indicate a similar structure and function of both proteins. High acyl-CoA:diacylglycerol acyltransferase activity (DGAT; 143 pmol (mg min)⁻¹) but low wax ester synthase activity (WS; 1.3 pmol (mg min)⁻¹) were detected in crude extracts of S. avermitilis, which were consistent with the high TAG and negligible WE content of the cells. This indicates that TAG accumulation in S. avermitilis MA-4680 is mediated by the classical acyl-CoA-dependent DGAT pathway. Heterologous expression experiments in recombinant Escherichia coli BL21(DE3) demonstrated both WS and DGAT enzyme activity of SAV7256. Furthermore, substrate specificities of the acyltransferase SAV7256 will be discussed. Chlud Kaddor and Karolin Biermann contributed equally to this work.     

Construction of ivermectin producer by domain swaps of avermectin polyketide synthase in Streptomyces avermitilis

Ivermectin, 22, 23-dihydroavermectin B1, is commercially important in human, veterinary medicine, and pesticides. It is currently synthesized by chemical reduction of the double bond between C22 and C23 of avermectins B1, which are a mixture of B1a (>80%) and B1b (<20%) produced by fermentation of Streptomyces avermitilis. The cost of ivermectin is much higher than that of avermectins B1 owing to the necessity of region-specific hydrogenation at C22–C23 of avermectins B1 with rhodium chloride as the catalyst for producing ivermectin. Here we report that ivermectin can be produced directly by fermentation of recombinant strains constructed through targeted genetic engineering of the avermectin polyketide synthase (PKS) in S. avermitilis Olm73-12, which produces only avermectins B and not avermectins A and oligomycin. The DNA region encoding the dehydratase (DH) and ketoreductase (KR) domains of module 2 from the avermectin PKS in S. avermitilis Olm73-12 was replaced by the DNA fragment encoding the DH, enoylreductase, and KR domains from module 4 of the pikromycin PKS of Streptomyces venezuelae ATCC 15439 using a gene replacement vector pXL211. Twenty-seven of mutants were found to produce a small amount of 22, 23-dihydroavermectin B1a and avermectin B1a and B2a by high performance liquid chromatography and liquid chromatography mass spectrometry analysis. This study might provide a route to the low-cost production of ivermectin by fermentation.     

大气压辉光放电低温等离子体诱变选育谷氨酰胺转胺酶高产菌株

以茂源链轮丝菌(Streptoverticillium mobaraense)03-10为出发菌株,采用一种新型的裸露电极大气压辉光放电的冷等离子体技术对链霉菌孢子进行诱变。根据双层平板法菌落显色及诱变处理后菌落形态差异快速筛选谷氨酰胺转胺酶高产突变株。突变率、正突变率分别达到42.8%和20.6%。最后复筛选育出具有较好遗传稳定性和形态稳定性的高产突变株G2-1,酶活达到2.73U/mL,比出发菌株提高了82%。     

Regioselective hydroxylation of daidzein using P450 (CYP105D7) from Streptomyces avermitilis MA4680

Regiospecific 3′‐hydroxylation reaction of daidzein was performed with CYP105D7 from Streptomyces avermitilis MA4680 expressed in Escherichia coli. The apparent K_m and k_cat values of CYP105D7 for daidzein were 21.83 ± 6.3 µM and 15.01 ± 0.6 min^?1 in the presence of 1 µM of CYP105D7, putidaredoxin (CamB) and putidaredoxin reductase (CamA), respectively. When CYP105D7 was expressed in S. avermitilis MA4680, its cytochrome P450 activity was confirmed by the CO‐difference spectra at 450 nm using the whole cell extract. When the whole‐cell reaction for the 3′‐hydroxylation reaction of daidzein was carried out with 100 µM of daidzein in 100 mM of phosphate buffer (pH 7.5), the recombinant S. avermitilis grown in R2YE media overexpressing CYP105D7 and ferredoxin FdxH (SAV7470) showed a 3.6‐fold higher conversion yield (24%) than the corresponding wild type cell (6.7%). In a 7 L (working volume 3 L) jar fermentor, the recombinants S. avermitilis grown in R2YE media produced 112.5 mg of 7,3′,4′‐trihydroxyisoflavone (i.e., 29.5% conversion yield) from 381 mg of daidzein in 15 h. Biotechnol. Bioeng. 2010. 105: 697–704. © 2009 Wiley Periodicals.     

Mutation breeding of high avermectin B<Subscript>1a</Subscript>-producing strain by the combination of high energy carbon heavy ion irradiation and sodium nitrite mutagenesis based on high throughput screening

Microbial mutation breeding has been widely used because it is one of the most efficient and practical breeding strategies in the fermentation industry. However, different mutagenesis methods cause various degrees of DNA damage to individual microorganisms, which lead to diverse characteristics of the mutants. In this study, the effects of four different mutagenesis methods on the mutation breeding of Streptomyces avermitilis for improving avermectin B1a production were investigated with an optimized liquid microtiter plate (MTP) culture system. First, an effective and feasible MTP system for mutant strain screening was evaluated through the optimization of the oxygen transfer rate and rapid titer determination. Then, high energy carbon heavy ion irradiation, diethyl sulfate, ultraviolet- (UV) irradiation combined with lithium chloride, and sodium nitrite were used as the mutagens for mutation breeding, respectively. Results showed that carbon heavy ion irradiation had the advantages of possessing the highest positive mutation rate and mean-production of positive mutant strains in the first generation. Sodium nitrite treatment resulted in mutant strains with better inherited stability than the other three methods. Through the combined treatment of carbon heavy ion irradiation and sodium nitrite treatment, an inheritstable mutant S. avermitilis S-233 with high avermectin B_1a production was successfully obtained. The fermentation verification in a 500-liter (L) bioreactor demonstrated that the avermectin B_1a produced by mutant S. avermitilis S-233 reached 6818 μg/mL, which was 23.8% higher than that of parent strains.     

A C6/C5 co‐fermenting Saccharomyces cerevisiae strain with the alleviation of antagonism between xylose utilization and robustness

During second‐generation bioethanol production from lignocellulosic biomass, the desired traits for fermenting microorganisms, such as Saccharomyces cerevisiae, are high xylose utilization and high robustness to inhibitors in lignocellulosic hydrolysates. However, as observed previously, these two traits easily showed the antagonism, one rising and the other falling, in the C6/C5 co‐fermenting S. cerevisiae strain. In this study, LF1 obtained in our previous study is an engineered budding yeast strain with a superior co‐fermentation capacity of glucose and xylose, and was then mutated by atmospheric and room temperature plasma (ARTP) mutagenesis to improve its robustness. The ARTP‐treated cells were grown in 50% (v/v) leachate from lignocellulose pretreatment with high inhibitors content for adaptive evolution. After 30 days, the generated mutant LF1‐6 showed significantly enhanced tolerance, with a six‐fold increase in cell density in the above leachate. Unfortunately, its xylose utilization dropped markedly, indicating the recurrence of the negative correlation between xylose utilization and robustness. To alleviate this antagonism, LF1‐6 cells were iteratively mutated with ARTP mutagenesis and then anaerobically grown using xylose as the sole carbon source, and xylose utilization was restored in the resulting strain 6M‐15. 6M‐15 also exhibited increased co‐fermentation performance of xylose and glucose with the highest ethanol productivity reported to date (0.525 g g^?1 h^?1) in high‐level mixed sugars (80 g L^?1 glucose and 40 g L^?1 xylose) with no inhibitors. Meanwhile, its fermentation time was shortened by 8 h compared to that of LF1. During the fermentation of non‐detoxified lignocellulosic hydrolysate with high inhibitor concentrations at pH ~3.5, 6M‐15 can efficiently convert glucose and xylose with an ethanol yield of 0.43 g g^?1. 6M‐15 is also regarded as a potential chassis cell for further design of a customized strain suitable for production of second‐generation bioethanol or other high value‐added products from lignocellulosic biomass.     

A new strain of <Emphasis Type="Italic">Streptomyces avermitilis</Emphasis> produces high yield of oligomycin A with potent anti-tumor activity on human cancer cell lines in vitro

A new actinomycete strain, isolated from soil in China, strongly inhibited in vitro proliferation of human hepatoma, chronic myelogenous leukemia, and colonic carcinoma cell lines. The strain, designated L033, was identified as a strain of Streptomyces avermitilis based on cultural property, morphology, carbon source utilization, 16s rRNA gene analysis, and DNA–DNA relatedness studies. The anticancer component from L033 was purified to homogeneity by preparative positive-phase high-performance liquid chromatography and crystallization. Nuclear magnetic resonance and mass spectrometric analysis showed that this compound had the same structure as oligomycin A. Different with other reported naturally occurring strains of S. avermitilis, L033 produced high quantity of oligomycin A (maximal 1,461 μg/ml). Therefore, L033 was considered of great potential as an industrial oligomycin-A-producing strain. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Preliminary study on polymorphism analysis of SpRunt-1 gene by PCR–SSCP in <Emphasis Type="Italic">Strongylocentrotus intermedius</Emphasis> and its association with growth traits

In current study, the SpRunt-1 gene was screened for the polymorphisms using PCR-single strand conformation polymorphism (PCR–SSCP) and DNA sequencing methods in Strongylocentrotus intermedius (S. intermedius). Three polymorphisms were found with two site mutations, G833A and C1505T mutation, and an insertion mutation (GT) between 931 nt and 932 nt. These two site mutations are synonymous mutations and the insertion mutation is frame shift mutation. One way ANOVA analysis of correlation between the single nucleotide polymorphisms (SNPs) and growth traits showed that the gonad weight of AA genotype (G at 833 nt) was significantly higher than that of BB genotype (A at 833 nt) (P = 0.029). The body weight of the CC genotype (C at 1505 nt) was significantly higher than that of DD genotype (T at 1505 nt) (P < 0.01) and the shell height of CD genotype was significantly higher than that of DD genotype (P = 0.032). These results provided the evidence that S. intermedius SpRunt-1 gene could be selected as a candidate gene for the growth traits.     

The microbiology of Bandji,palm wine of Borassus akeassii from Burkina Faso: identification and genotypic diversity of yeasts,lactic acid and acetic acid bacteria

Aim

To investigate physicochemical characteristics and especially genotypic diversity of the main culturable micro‐organisms involved in fermentation of sap from Borassus akeassii, a newly identified palm tree from West Africa.

Methods and Results

Physicochemical characterization was performed using conventional methods. Identification of micro‐organisms included phenotyping and sequencing of: 26S rRNA gene for yeasts, 16S rRNA and gyrB genes for lactic acid bacteria (LAB) and acetic acid bacteria (AAB). Interspecies and intraspecies genotypic diversities of the micro‐organisms were screened respectively by amplification of the ITS1‐5.8S rDNA‐ITS2/16S‐23S rDNA ITS regions and repetitive sequence‐based PCR (rep‐PCR). The physicochemical characteristics of samples were: pH: 3·48–4·12, titratable acidity: 1·67–3·50 mg KOH g^?1, acetic acid: 0·16–0·37%, alcohol content: 0·30–2·73%, sugars (degrees Brix): 2·70–8·50. Yeast included mainly Saccharomyces cerevisiae and species of the genera Arthroascus, Issatchenkia, Candida, Trichosporon, Hanseniaspora, Kodamaea, Schizosaccharomyces, Trigonopsis and Galactomyces. Lactobacillus plantarum was the predominant LAB species. Three other species of Lactobacillus were also identified as well as isolates of Leuconostoc mesenteroides, Fructobacillus durionis and Streptococcus mitis. Acetic acid bacteria included nine species of the genus Acetobacter with Acetobacter indonesiensis as predominant species. In addition, isolates of Gluconobacter oxydans and Gluconacetobacter saccharivorans were also identified. Intraspecies diversity was observed for some species of micro‐organisms including four genotypes for Acet. indonesiensis, three for Candida tropicalis and Lactobacillus fermentum and two each for S. cerevisiae, Trichosporon asahii, Candida pararugosa and Acetobacter tropicalis.

Conclusion

fermentation of palm sap from B. akeassii involved multi‐yeast‐LAB‐AAB cultures at genus, species and intraspecies level.

Significance and Impact of the Study

First study describing microbiological and physicochemical characteristics of palm wine from B. akeassii. Genotypic diversity of palm wine LAB and AAB not reported before is demonstrated and this constitutes valuable information for better understanding of the fermentation which can be used to improve the product quality and develop added value by‐products.     

Spaceflight‐induced enhancement of 2‐keto‐L‐gulonic acid production by a mixed culture of Ketogulonigenium vulgare and Bacillus thuringiensis

Two bacterial strains used for industrial production of 2‐keto‐L‐gulonic acid (2‐KLG), Ketogulonigenium vulgare 2 and Bacillus thuringiensis 1514, were loaded onto the spacecraft Shenzhou VII and exposed to space conditions for 68 h in an attempt to increase their fermentation productivities of 2‐KLG. An optimal combination of mutants B. thuringiensis 320 and K. vulgare 2194 (KB2194‐320) was identified by systematically screening the pH and 2‐KLG production of 16 000 colonies. Compared with the coculture of parent strains, the conversion rate of L‐sorbose to 2‐KLG by KB2194‐320 in shake flask fermentation was increased significantly from 82·7% to 95·0%. Furthermore, a conversion rate of 94·5% and 2‐KLG productivity of 1·88 g l^?1 h^?1 were achieved with KB2194‐320 in industrial‐scale fermentation (260 m³ fermentor). An observed increase in cell number of K2194 (increased by 47·8%) during the exponential phase and decrease in 2‐KLG reductase activity (decreased by 46·0%) were assumed to explain the enhanced 2‐KLG production. The results suggested that the mutants KB2194‐320 could be ideal substitutes for the currently employed strains in the 2‐KLG fermentation process and demonstrated the feasibility of using spaceflight to breed high‐yielding 2‐KLG‐producing strains for vitamin C production.

Significance and Impact of the Study

KB2194‐320, a combination of two bacterial strains bred by spaceflight mutation, exhibited significantly improved 2‐KLG productivity and hence could potentially increase the efficiency and reduce the cost of vitamin C production by the two‐step fermentation process. In addition, a new pH indicator method was applied for rational screening of K2, which dramatically improved the efficiency of screening.     

Enhanced volatile phenols in wine fermented with Saccharomyces cerevisiae and spoiled with Pichia guilliermondii and Dekkera bruxellensis

Aims: To investigate whether the presence of Pichia guilliermondii impacts on the production of volatile phenols from mixed wine fermentations with Dekkera bruxellensis and Saccharomyces cerevisiae. Methods and Results: Four inoculation strategies were performed in small‐scale fermentations involving P. guilliermondii, D. bruxellensis and S. cerevisiae using Syrah grape juice supplemented with 100 mg l^?1 of p‐coumaric acid. High pressure liquid chromatography was used for the quantification or volatile phenols. Significant high levels of 4‐ethylphenol and 4‐ethylguaicol (720 and 545 μg l^?1, respectively), as well as the highest levels of 4‐vinylphenol (>4500 μg l^?1), were observed when P. guilliermondii species was inoculated from the beginning of the fermentation. Conclusions: The metabolic interaction occurring between the high vinylphenol producer species P. guilliermondii and D. bruxellensis exhibiting a high vinylphenol reductase activity resulted in an increased production of volatile phenols in wine. Significance and Impact of the Study: Pichia guilliermondii must be considered a very important spoilage yeast in the wine industry capable of producing large amounts of volatile phenols.     

Clinicopathological characteristics associated with BRAFK601E and BRAFL597 mutations in melanoma

BRAF mutations at codons L597 and K601 occur uncommonly in melanoma. Clinical and pathological associations of these mutations were investigated in a cohort of 1119 patients with known BRAF mutation status. A BRAF mutation was identified in 435 patients; Mutations at L597 and the K601E mutation were seen in 3.4 and 3.2% of these, respectively. K601E melanomas tended to occur in male patients, a median age of 58 yr, were generally found on the trunk (64%) and uncommonly associated with chronically sun‐damaged (CSD) skin. BRAF L597 melanomas occurred in older patients (median 66 yr), but were associated with CSD skin (extremities or head and neck location – 73.3%, P = 0.001). Twenty‐three percent of patients with V600E‐ and 43% of patients with K601E‐mutant melanomas presented with nodal disease at diagnosis compared to just 14% of patients with BRAF wild‐type tumors (P = 0.001 and 0.006, respectively). Overall, these mutations represent a significant minority of BRAF mutations, but have distinct clinicopathological phenotypes and clinical behaviors.     

Feasibility of monitoring advanced melanoma patients using cell‐free DNA from plasma

To determine the feasibility of liquid biopsy for monitoring of patients with advanced melanoma, cell‐free DNA was extracted from plasma for 25 Stage III/IV patients, most (84.0%) having received previous therapy. DNA concentrations ranged from 0.6 to 390.0 ng/ml (median = 7.8 ng/ml) and were positively correlated with tumor burden as measured by imaging (Spearman rho = 0.5435, p = .0363). Using ultra‐deep sequencing for a 61‐gene panel, one or more mutations were detected in 12 of 25 samples (48.0%), and this proportion did not vary significantly for patients on or off therapy at the time of blood draw (52.9% and 37.5% respectively; p = .673). Sixteen mutations were detected in eight different genes, with the most frequent mutations detected in BRAF, NRAS, and KIT. Allele fractions ranged from 1.1% to 63.2% (median = 29.1%). Among patients with tissue next‐generation sequencing, nine of 11 plasma mutations were also detected in matched tissue, for a concordance of 81.8%.     

Pooled analysis of clinical outcome for EGFR TKI‐treated patients with EGFR mutation‐positive NSCLC

Patients with non‐small‐cell lung cancer (NSCLC) appear to gain particular benefit from treatment with epidermal growth factor receptor (EGFR) tyrosine‐kinase inhibitors (TKI) if their disease tests positive for EGFR activating mutations. Recently, several large, controlled, phase III studies have been published in NSCLC patients with EGFR mutation‐positive tumours. Given the increased patient dataset now available, a comprehensive literature search for EGFR TKIs or chemotherapy in EGFR mutation‐positive NSCLC was undertaken to update the results of a previously published pooled analysis. Pooling eligible progression‐free survival (PFS) data from 27 erlotinib studies (n = 731), 54 gefitinib studies (n = 1802) and 20 chemotherapy studies (n = 984) provided median PFS values for each treatment. The pooled median PFS was: 12.4 months (95% accuracy intervals [AI] 11.6–13.4) for erlotinib‐treated patients; 9.4 months (95% AI 9.0–9.8) for gefitinib‐treated patients; and 5.6 months (95% AI 5.3–6.0) for chemotherapy. Both erlotinib and gefitinib resulted in significantly longer PFS than chemotherapy (permutation testing; P = 0.000 and P = 0.000, respectively). Data on more recent TKIs (afatinib, dacomitinib and icotinib) were insufficient at this time‐point to carry out a pooled PFS analysis on these compounds. The results of this updated pooled analysis suggest a substantial clear PFS benefit of treating patients with EGFR mutation‐positive NSCLC with erlotinib or gefitinib compared with chemotherapy.     

Detection of induced mutations in CaFAD2 genes by next‐generation sequencing leading to the production of improved oil composition in Crambe abyssinica

Crambe abyssinica is a hexaploid oil crop for industrial applications. An increase of erucic acid (C22:1) and reduction of polyunsaturated fatty acid (PUFA) contents in crambe oil is a valuable improvement. An increase in oleic acid (C18:1), a reduction in PUFA and possibly an increase in C22:1 can be obtained by down‐regulating the expression of fatty acid desaturase2 genes (CaFAD2), which code for the enzyme that converts C18:1 into C18:2. We conducted EMS‐mutagenesis in crambe, followed by Illumina sequencing, to screen mutations in three expressed CaFAD2 genes. Two novel analysis strategies were used to detect mutation sites. In the first strategy, mutation detection targeted specific sequence motifs. In the second strategy, every nucleotide position in a CaFAD2 fragment was tested for the presence of mutations. Seventeen novel mutations were detected in 1100 one‐dimensional pools (11 000 individuals) in three expressed CaFAD2 genes, including non‐sense mutations and mis‐sense mutations in CaFAD2‐C1, ‐C2 and ‐C3. The homozygous non‐sense mutants for CaFAD2‐C3 resulted in a 25% higher content of C18:1 and 25% lower content of PUFA compared to the wild type. The mis‐sense mutations only led to small changes in oil composition. Concluding, targeted mutation detection using NGS in a polyploid was successfully applied and it was found that a non‐sense mutation in even a single CaFAD2 gene can lead to changes in crambe oil composition. Stacking the mutations in different CaFAD2 may gain additional changes in C18:1 and PUFA contents.     

Effects of hops (Humulus lupulus L.) extract on volatile fatty acid production by rumen bacteria

Aims: To determine the effects of hops extract on in vitro volatile fatty acid (VFA) production by bovine rumen micro‐organisms. Methods and Results: When mixed rumen microbes were suspended in media containing carbohydrates, the initial rates of VFA production were suppressed by β‐acid‐rich hops extract. The rates of VFA production increased over extended incubations (24 h), and hops extract caused an increase in the propionate to acetate ratio. Hops extract inhibited the growth and metabolism of Streptococcus bovis, but Selenomonas ruminantium and Megasphaera elsdenii were not affected. Likewise, the propionate production of M. elsdenii/S. bovis co‐cultures, but not M. elsdenii/S. ruminantium co‐cultures, was decreased in the presence of hops extract. Conclusions: These results are consistent with the hypothesis that the hops inhibit Gram‐positive lactic acid bacteria (S. bovis), and the rumen microbial community requires a period of adaptation before normal VFA production resumes. Selenomonas bovis and S. ruminantium both produce lactate, which is the substrate for propionate production by M. elsdenii. However, S. ruminantium has an outer membrane, while S. bovis does not. Significance and Impact of Study: The enhanced production of the gluconeogenesis precursor, propionic acid, provides further evidence that plant secondary metabolites from hops could be used to improve rumen fermentation.     

Development of starter culture for improved processing of Lafun,an African fermented cassava food product

Aims: To select appropriate micro‐organisms to be used as starter culture for reliable and reproducible fermentation of Lafun. Methods and Results: A total of 22 cultures consisting of yeast, lactic acid bacteria (LAB) and Bacillus cereus strains predominant in traditionally fermented cassava during Lafun processing were tested as potential starter cultures. In an initial screening, Saccharomyces cerevisiae 2Y48P22, Lactobacillus fermentum 2L48P21, Lactobacillus plantarum 1L48P35 and B. cereus 2B24P31 were found to be the most promising of the cultures and were subsequently tested in different combinations as mixed starter cultures to ferment submerged cassava roots. Saccharomyces cerevisiae, inoculated singly or combined with B. cereus, gave the softest cassava root after 48 h of fermentation according to determination of compression profile and stress at fracture. Overall, sensory quality testing showed that Lafun obtained from S. cerevisiae‐fermented cassava gave the most preferred stiff porridge. Saccharomyces cerevisiae 2Y48P22 showed pectinase production in a model system. Conclusions: The results suggest that S. cerevisiae 2Y48P22 is the most efficient organism for cassava softening during the fermentation. Therefore, it could be combined with LAB and used as starter for Lafun processing. Significance and Impact of the Study: Starter cultures are made available for controlled fermentation of Lafun.     

Genotypic analysis of degenerative Cordyceps militaris cultured in the pupa of Bombyx mori

The chemical composition and pharmacological effects of Cordyceps militaris are similar to those of Cordyceps sinensis, with the former undergoing greater development and utilization. Strain degeneration is a common phenomenon that occurs with high frequency during the subculturing of C. militaris, however, and the mechanism underlying strain degeneration remains unclear. In this study, we used touch‐down PCR to compare the ITS1 + 5.8S + ITS2, 18S, 28S and mating‐type (MAT) regions sequence of wild‐type and degenerated strains of C. militaris. We also used quantitative real‐time PCR to analyze expression levels of the CmMAT gene. Sequence analysis showed that the ITS1 + 5.8S + ITS2 and 28S regions of degenerated and wild‐type strains were completely identical, the 18S region of the degenerated strain contained seven single‐base mutations, including six base substitutions and one single‐base insertion. Compared with the wild‐type strain, the degenerated strain contained a deletion of the MAT1–2‐1 region, three base substitutions in the MAT1–1‐1 region, and a base substitution in the MAT1–1‐2 region that causes a glycine‐to‐valine amino acid substitution. Quantitative real‐time PCR analysis detected no CmMAT1–2‐1 gene expression in the degenerated strain, confirming the deletion of the CmMAT1–2‐1 gene. Expression levels of the CmMAT1–1‐1 and CmMAT1–1‐2 genes were significantly down‐regulated to only 7.5 % and 4.4 %, respectively, that of the wild‐type strain. These results indicate that 18S and MAT region mutations, as well as down‐regulated of CmMAT gene expression levels, may play important roles in C. militaris degeneration. This study provides a theoretical basis for further elucidation of the molecular mechanisms of C. militaris degeneration.