氮、磷源浓度对裂殖壶菌生长及油脂积累的影响

裂殖壶菌是替代深海鱼油产业化生产二十二碳六烯酸(docosahexaenoic acid, DHA)油脂的极具潜力的微生物。该研究采用1株裂殖壶菌DP-16发酵产油脂,以葡萄糖为碳源,以酵母浸粉和谷氨酸钠为氮源,以KH₂PO₄为磷源,探究了氮、磷源浓度对菌体生长、葡萄糖消耗和油脂积累的影响。结果显示,在正常氮、磷源浓度下培养菌体,0～24 h为细胞增殖期,24～84 h为油脂积累期,在84 h油脂产量和油脂含量分别达到14.1 g/L和33.5%,84～96 h进入油脂反耗期。改变氮、磷源浓度,低磷条件下72 h的油脂产量和油脂含量分别达到14.8 g/L和44.3%,比对照组分别提高了5.0%和32.2%,而高氮、低氮、高磷等条件均不利于裂殖壶菌产油脂。研究结果表明,氮、磷源浓度对裂殖壶菌细胞生长和油脂积累产生重要影响,油脂产量取决于菌体生物量和细胞内油脂含量的乘积,为提高油脂产量,需要在获得高细胞浓度(生物量)和达到高油脂含量之间找到一个合适的平衡,以确定适宜的氮、磷源浓度。该研究对促进裂殖壶菌发酵产DHA油脂具有重要参考意义。     

葡萄糖亚适量补加胁迫裂殖壶菌胞内类胡萝卜素积累

为探究裂殖壶菌积累类胡萝卜素的营养胁迫调控手段,考察了发酵中期(72 h起),不同葡萄糖补加质量浓度、酵母提取物补加质量浓度对裂殖壶菌生长、油脂合成和类胡萝卜素合成的影响。结果表明:仅补加较低质量浓度葡萄糖时,裂殖壶菌生物量和油脂产量虽较低,但胞内类胡萝卜素含量较高;在5 L发酵罐中、发酵中期,采用溶氧反馈控制葡萄糖流加策略,人为制造葡萄糖亚适量补加条件,在发酵98 h时胞内类胡萝卜素含量达到最大,为151.0μg/g,相比葡萄糖充足供应条件下的水平提高了4倍以上。综合发酵实验结果和裂殖壶菌代谢途径分析,可推测:油脂合成期葡萄糖亚适量补加可限制细胞生长、弱化裂殖壶菌胞内油脂合成途径,胁迫碳源流向类胡萝卜素合成途径,促进类胡萝卜素的大量积累。     

糖蜜发酵裂殖壶菌生产二十二碳六烯酸

对糖蜜作为碳源发酵裂殖壶菌生产二十二碳六烯酸(docosahexaenic acid,DHA)进行了初步研究:选择不同来源的甘蔗糖蜜与粗糖蜜培养裂殖壶菌生产DHA,考察了糖蜜来源、糖蜜添加比例对裂殖壶菌发酵生物量、菌体油脂含量与DHA含量的影响。结果表明,甘蔗糖蜜中的杂质(灰分、胶体)对菌体生长与油脂积累存在明显的抑制作用,即使大幅降低糖蜜添加比例效果也不理想,限制了其作为替代碳源在实际生产上的应用。在此基础上考察了杂质含量相对较低的粗糖蜜的情况,在添加比例低于80%的情况下,其培养效果与对照葡萄糖非常接近,可以部分替代葡萄糖用于裂殖壶菌发酵生产。     

裂殖壶菌的双碳源发酵生产二十二碳六烯酸控制策略

研究了葡萄糖、甘油双碳源发酵对裂殖壶菌发酵二十二碳六烯酸(docosahexaenoic acid, DHA)的影响。首先以葡萄糖和甘油为单一碳源,发现以葡萄糖为碳源,菌体增殖速度和底物消耗速度都明显高于以甘油为碳源,以甘油为碳源细胞油脂中DHA的比例显著高于葡萄糖。为了发挥2种碳源各自优势,对葡萄糖和甘油双碳源发酵进行研究,结果显示2种碳源混合或葡萄糖耗尽后补加甘油结果都不如单一碳源好。但若先用葡萄糖为碳源进行培养,当发酵液中的葡萄糖质量浓度降至10～5 g/L时补加甘油既可以缩短发酵周期,又提高了油脂中的DHA比例。采用初始葡萄糖质量浓度为20 g/L,过程补加100 g/L甘油的发酵控制策略,5 L罐发酵,发酵周期可缩短至56 h,细胞油脂中DHA比例最高可达45.50%,充分发挥了2种碳源的优势。该研究得到了一种裂殖壶菌生产DHA葡萄糖、甘油分段发酵控制策略,大幅提高菌体细胞油脂中DHA的比例,同时有效缩短了发酵周期,具有非常好的工业应用价值。     

不同碳氮源浓度和培养温度对裂殖壶菌产DHA的影响

研究不同碳氮源浓度和培养温度对裂殖壶菌产DHA的影响。用干重法测定裂殖壶菌的生物量,溶剂法提取油脂,并用GC分析DHA含量。结果表明:最适初始葡萄糖质量浓度和氮源质量浓度分别为80、15 g/L;菌种在26℃下培养48 h后,再将发酵温度降到22℃下培养120 h,其DHA含量为43.62%,DHA产量为5.23 g/L。在最佳条件下,50 L放大培养(先26℃培养48 h,后22℃培养96 h)后油脂产量可达14.8 g/L,DHA产量可达6.5 g/L。综上所述,裂殖壶菌具有较好的工业化生产潜力。     

利用酒糟处理液作为氮源培养裂殖壶菌生产DHA的发酵工艺优化

为降低发酵培养裂殖壶菌生产DHA的成本,以酱香型白酒酒糟为实验材料,将其简单预处理后作为裂殖壶菌发酵培养基氮源,首先分析了酒糟处理液与胰蛋白胨的游离氨基酸组成与含量,然后以生物量、油脂产量和DHA产量为指标,对酒糟处理液、胰蛋白胨、酵母提取物和牛肉膏作为氮源培养裂殖壶菌生产DHA进行了比较,优化了酒糟处理液作为氮源时的发酵工艺条件,并对发酵废液进行三次循环利用。结果表明：酒糟处理液可以作为满足裂殖壶菌生长的氮源;与酵母提取物、牛肉膏相比,酒糟处理液作为氮源有明显优势;利用酒糟处理液作为氮源的最佳发酵工艺条件为酒糟（含水量约10%）与水质量比1∶ 9、酒糟处理液添加量70%（与基础发酵培养基中水的置换比例）、初始pH 7.0、培养时间108 h,在此条件下裂殖壶菌生物量、油脂产量和DHA产量分别达到22.14、8.88 g/L和284 g/L;最佳条件下三次循环添加15.0%（与基础发酵培养基中水的置换比例）发酵废液于酒糟处理液培养基中,裂殖壶菌DHA产量分别为4.27、3.70 g/L和2.75 g/L。综上,利用酒糟处理液培养裂殖壶菌生产DHA是酒糟资源化利用的新方法。     

利用酒糟处理液作为氮源培养裂殖壶菌生产DHA的发酵工艺优化

为降低发酵培养裂殖壶菌生产DHA的成本，以酱香型白酒酒糟为实验材料，将其简单预处理后作为裂殖壶菌发酵培养基氮源，首先分析了酒糟处理液与胰蛋白胨的游离氨基酸组成与含量，然后以生物量、油脂产量和DHA产量为指标，对酒糟处理液、胰蛋白胨、酵母提取物和牛肉膏作为氮源培养裂殖壶菌生产DHA进行了比较，优化了酒糟处理液作为氮源时的发酵工艺条件，并对发酵废液进行三次循环利用。结果表明：酒糟处理液可以作为满足裂殖壶菌生长的氮源；与酵母提取物、牛肉膏相比，酒糟处理液作为氮源有明显优势；利用酒糟处理液作为氮源的最佳发酵工艺条件为酒糟(含水量约10%)与水质量比1∶9、酒糟处理液添加量70%(与基础发酵培养基中水的置换比例)、初始pH 7.0、培养时间108 h,在此条件下裂殖壶菌生物量、油脂产量和DHA产量分别达到22.14、8.88 g/L和2.84 g/L;最佳条件下三次循环添加15.0%(与基础发酵培养基中水的置换比例)发酵废液于酒糟处理液培养基中，裂殖壶菌DHA产量分别为4.27、3.70 g/L和2.75 g/L。综上，利用酒糟处理液培养裂殖壶菌生产DHA是酒糟资源化利用的新方法。     

亚铁离子和吲哚丁酸促进裂殖壶菌产DHA及发酵验证

为提高裂殖壶菌产DHA的生产强度,筛选比较出对裂殖壶菌生长和产油有显著影响的促进因子,发现Fe~(2+)对Schizochytruim sp.AB-610生长有显著的促进作用,吲哚丁酸(IBA)对裂殖壶菌生长和产油有双重促进作用。在此基础上进行了两因素(Fe~(2+)和IBA)、三水平响应面实验,通过响应模型得到最优添加方案。在摇瓶发酵中得到验证后,继而在NBS 7.5 L发酵罐内测定对照组Schizochytruim sp.AB-610的发酵特性曲线,依据其发酵规律,将发酵周期分为菌体适应期、快速生长期、油脂快速积累期、油脂返耗期。测定了Fe~(2+)和IBA对7.5 L发酵罐中裂殖壶菌培养和发酵的特征曲线,并与对照组进行多参数比对,发现添加双促进因子可加大快速生长期的细胞生长速率,延长生物量增长的时间,生物量和DHA产量皆得到提高。最终使Schizochytruim sp.的DHA生产强度提高了51.22%。     

裂殖壶菌补糖发酵研究

为了探索不同碳源浓度对裂殖壶菌(Schizochytrium)细胞营养生长和油脂积累的影响,对发酵调控进行研究,同时测定发酵液生物量、含油量、DHA含量和DHA产量。结果表明:发酵过程中通过补糖可以提高发酵液含油量和DHA产量,但糖浓度过高也会抑制发酵;当还原糖质量浓度调控在40 g/L左右时,生物量、含油量、DHA含量和DHA产量均达最高,分别为8.95 g/100 m L、22.42 g/L、41.71%、9.35 g/L,比对照组高出了76.18%、61.88%、4.3%、68.77%。     

生物柴油副产品粗甘油浓度对裂殖壶菌生长与积累油脂的影响

在研究了生物柴油副产品粗甘油培养裂殖壶菌(Schizochytrium sp.)WZU6961产油脂的优化培养条件的基础上,对粗甘油浓度对裂殖壶菌生长和积累油脂的影响进行研究。结果表明,在温度、溶氧及培养基其他成分相同的培养条件下,随着粗甘油浓度的增加,菌体油脂含量和脂肪酸组成没有显著的变化;但甘油的生物量和油脂得率系数以及生物量生产率和油脂生产率逐渐下降,说明粗甘油浓度过高对细胞的生长有抑制效应;当粗甘油质量浓度分别为30 g/L和60 g/L时,生物量生产率分别为0.94 g/(L·h)和0.87 g/(L·h),油脂生产率分别为0.69 g/(L·h)和0.64 g/(L·h),两者的生物量生产率和油脂生产率比较接近,因而可以得出适宜的粗甘油质量浓度为30 g/L。在粗甘油质量浓度30 g/L下,发酵时间26 h,生物量、菌体油脂含量和DHA占油脂的比例分别为(24.38±1.42)g/L、(74.08±2.20)%和23.72%。     

Arsenic content of some edible mushroom species

The arsenic contents of 162 fruit body samples of 37 common edible mushroom taxa were analyzed. The samples were gathered from different habitats of Hungary (mainly from mountains) between 1984 and 1999. The arsenic content of the samples was measured by the inductively coupled plasma spectrometry method. Very low [lower than 0.05 mg/kg dry matter (DM)] concentrations were found in the samples of 13 taxa, while higher (or very high) contents were quantified in other common taxa (the highest arsenic content was recorded in the fruit body of Laccaria amethysthea at 146.9 mg/kg DM). The species of eight genera (Agaricus, Calvatia, Collybia, Laccaria, Langermannia, Lepista, Lycoperdon, Macrolepiota) belong to the so-called accumulating taxa, and this tendency is evident on all habitats. This arsenic accumulation capability is found in two orders of Basidiomycetes (Agaricales and Gasteromycetales), which is to say this phenomenon occurs in the families Agaricaceae, Tricholomataceae and Gasteromycetaceae. The accumulating taxa found all have a saprotrophic type of nutrition; arsenic accumulation is not detectable in xilophagous or in mycorrhizal species. The consumption of the accumulating species found has only a low toxicological risk for three reasons: the consumed fresh fruit bodies contain about a tenfold lower arsenic level than the dried ones, the majority of arsenic occurs not in poisonous inorganic, but in less dangerous (or not poisonous) organic forms, and the frequency of consumption is low.     

Organization and localization of the dnaA and dnaK gene regions on the multichromosomal genome of Burkholderia multivorans ATCC 17616

The Burkholderia multivorans strain ATCC 17616 carries three circular chromosomes with sizes of 3.4, 2.5, and 0.9 Mb. To reveal the distribution and organization of the genes for fundamental cell functions on the genome of this bacterium, the dnaA and dnaK gene regions of ATCC 17616 were cloned and characterized. The gene organization of the dnaA region was rnpA-rmpH-dnaA-dnaN-gyrB with a single consensus DnaA-binding box (TTATCCACA) between the rmpH and dnaA genes. This intergenic region, however, did not work as an autonomously replicating sequence in ATCC 17616. On the other hand, the gene organization of the dnaK region was grpE-orf1 (gene for thioredoxin homologue)-dnaK-dnaJ-pabB (gene for p-aminobenzoate synthetase component homologue). A putative heat-shock promoter that showed good homology to the sigma32-dependent promoter consensus sequence in Escherichia coli was found upstream of the grpE gene, suggesting that these five genes constitute an operon. In M9 succinate minimal medium the dnaJ mutant grew more slowly than the wild-type strain, indicating that this operon is functional. Pulsed-field gel electrophoresis and Southern blot analyses indicated that both the dnaA and dnaK gene regions exist as single copies on the 3.4 Mb chromosome.     

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle (Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth (Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil (Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil (S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.     

Contamination with storage fungi of human food from Cameroon

In a mycological study, a total of 95 human food samples were investigated to evaluate the incidence of fungal contamination in Cameroon by conventional identification method and partly confirmed by DNA sequencing. The isolated fungal spp. were further studied to determine their toxigenic potentials. The investigation revealed the predominance of Aspergillus and Penicillium with 96% of samples contaminated with at least one species of these fungi, whereas the incidence of co-contamination of samples was 85%. Aspergillus flavus and Aspergillus parasiticus (Flavi section) were the most predominant species contaminating mainly maize and peanuts. In addition, P. crustosum and P. polonicum were the most common contaminants belonging to the genus Penicillium. On the other hand, A. ochraceus (Circumdati section) registered a low incidence rate of 5%, including other members of the Aspergillus group. Other members of the genera Rhizopus and Alternaria spp. were also registered in the study. A majority of fungal strains of A. ochraceus, A. parasiticus, P. crustosum and P. polonicum isolated were toxigenic, producing the mycotoxins tested for, while none was detected in cultures of A. fumigatus. The high incidence rate of fungi contamination coupled with their potentials in producing mycotoxins gives a strong indication that the samples tested may likely be contaminated with various mycotoxins. There is need for further study to assess the incidence of mycotoxins contamination in similar food samples.     

鸡源大肠埃希氏菌mcr-1基因携带及分析

目的 了解在农业农村部禁止使用多黏菌素作为动物促生长使用后四川部分地区鸡源大肠埃希氏菌（E.coli）mcr-1基因的携带情况,为制定进一步防控措施提供依据。方法 采集四川部分地区市场售卖点肉鸡直肠拭子,用含有多黏菌素（终浓度4 μg/mL）的EC肉汤增菌接种含多黏菌素（终浓度4 μg/mL）的麦康凯平板,挑取可疑菌落,采用PCR方法鉴定菌株并检测mcr-1基因;微量肉汤稀释法测定mcr-1基因阳性菌株对临床常见抗菌药物耐药情况。脉冲场凝胶电泳（PFGE）对mcr-1基因阳性菌株进行同源分析。耐药基因质粒结合实验验证mcr-1基因传播途径。结果 从70份肉鸡样本中的13份检出mcr-1基因阳性大肠埃希氏菌,检出率18.57%（13/70）,对实验的13种抗生素,除13株mcr-1阳性菌株对头孢西丁有12株敏感以外,对其他抗生素都表现出不同程度的耐药,其中四环素和甲氧苄啶/磺胺甲恶唑耐药率最高,达到了100%（13/13）;其次是氨苄西林和氯霉素,耐药率为84.62%（11/13）。PFGE显示13株mcr-1阳性大肠埃希氏菌分属13个不同的型别;质粒结合实验显示mcr-1基因能够通过质粒传播。结论 mcr-1基因在鸡大肠内大肠杆菌中检测率比较高,且鸡大肠中mcr-1阳性大肠埃希氏菌的耐药情况比较严重。     

Assessment of the microbiological safety of salad vegetables and sauces from kebab take-away restaurants in the United Kingdom

The purpose of this study was to establish the microbiological safety of salad vegetables and sauces served in kebab take-away restaurants. Comparison with published microbiological guidelines revealed that 4.7% of 1213 salad vegetable samples were of unsatisfactory microbiological quality due to Escherichia coli and/or Staphylococcus aureus levels at ≥10² cfu g⁻¹. Another 0.3% of salad samples were of unacceptable quality due to S. aureus at ≥10⁴ cfu g⁻¹ (2 samples) or the presence of Salmonella Kentucky (1 sample). Cucumber was the most contaminated salad vegetable with regards to unsatisfactory levels of E. coli (6.0%) or S. aureus (4.5%). Five percent of 1208 sauce samples were of unsatisfactory microbiological quality due to E. coli, S. aureus at ≥10² cfu g⁻¹ and/or Bacillus cereus and other Bacillus spp. at ≥10⁴ cfu g⁻¹. A further 0.6% of sauce samples were of unacceptable quality due to Bacillus spp. (Bacillus subtilis, Bacillus pumilus, Bacillus licheniformis) at ≥10⁵ cfu g⁻¹ or the presence of Salmonella Agbeni (1 sample). More samples of chilli sauce (8.7%) were of unsatisfactory or unacceptable microbiological quality than any other sauce types. The results emphasize the need for good hygiene practices in kebab take-away restaurants handling these types of ready-to-eat products.     

Comparison of the most odour-active volatiles in different hop varieties by application of a comparative aroma extract dilution analysis

Application of a comparative aroma extract dilution analysis on the volatiles isolated from five different hops (Hallertau Perle, Hallertau Hersbrucker Spät, Slowenian Golding, Hallertau Smaragd, US Cascade) revealed linalool and myrcene with the highest Flavour Dilution (FD)-factors in all varieties, followed by 2-isopropyl-3-methoxypyrazine, 3-methylbutanoic acid and geraniol. Some odourants, however, showed high FD-factors only in certain varieties, for example, (5Z)-octa-1,5-dien-3-one and germacrene B in Hersbrucker Spät, (3E,5Z)-undeca-1,3,5-triene in Hersbrucker Spät and Cascade and nonanal in Cascade. The overall odour profile of the Cascade sample clearly differed from the other varietes, and was dominated by a black currant like odour note. The identification experiments revealed 4-methyl-4-sulfanylpentan-2-one, so far unknown as hop constituent, as key contributor to this odour. In addition, an odour-active undecatetraene was present, in particular, in Perle and Cascade. Synthesis and structural assignment of the four stereoisomers of (3E)-undeca-1,3,5,9-tetraene allowed the identification of the fresh, pineapple-like smelling compound as (3E,5Z,9E)-undeca-1,3,5,9-tetraene. Among the four isomers synthesised, this compound showed by far the lowest odour threshold of 0.01 ng/L in air.     

Microbial profiles of frozen trimmings and silver sides prepared at Indian buffalo meat packing plants

To assess microbiological quality of buffalo meat trimmings (TT = 114) and silver sides (SS = 41), samples were collected from four different Indian meat packing plants. The aim of this study was: (i) to evaluate standard plate count (SPC), psychrotrophic count (PTC), Enterococcus feacalis count (EFC), Staphylococcus aureus count (SAC) and Escherichia coli count (ECC) and the presence of Salmonella spp. and Listeria monocytogenes; and (ii) also to determine vero toxic E. coli (VTEC) by polymerase chain reaction (PCR). TT samples had significantly higher (P < 0.001) SPC, PTC, EFC, and SAC than SS, while across the meat types there was no difference (P > 0.05) in ECC. E. coli was recovered from 32.4% TT and 19.5% SS samples. The prevalence rate of Salmonella spp. and L. monocytogenes in TT was 1.75% and 0.87%, respectively. But no SS sample was found to be positive for any of these two pathogens. VTEC was found in 2.58% of all the tested samples. This finding suggests that TT contain higher microbes but only small numbers of pathogens of latent zoonotic importance. The present study confirmed the importance of maintaining good process hygiene at meat plants for microbiological status of buffalo meat.     

Developmental and population growth rates of phosphine-resistant and -susceptible populations of stored-product insect pests

Phosphine resistance positively contributes towards an individual's fitness under phosphine fumigation. However, phosphine resistance may place resistant individuals at a fitness disadvantage in the absence of this fumigant, which can be exploited to halt or slow down the spread of resistance. This study aimed to determine if there is a fitness cost associated with phosphine resistance in populations of the red flour beetle (Tribolium castaneum (Herbst)), the lesser grain borer (Rhyzopertha dominica (F.)) and the sawtoothed grain beetle (Oryzaephilus surinamensis (L.)). The developmental rate and population growth of phosphine-resistant and -susceptible populations of these three species of stored-product insects were therefore determined under phosphine-free environment. The majority of the phosphine-resistant populations exhibited lower developmental and population growth rates than the susceptible populations indicating that phosphine resistance is associated with fitness cost in all three species, which can potentially compromise the fixation and dispersal of the resistant genotypes. Nonetheless, some phosphine-resistant populations did not show a fitness cost. Therefore, resistance management strategies based on suppression of phosphine use aiming at eventual reestablishment of phosphine susceptibility and subsequent reintroduction of this fumigant will be useful only for insect populations exhibiting a fitness cost associated with phosphine resistance. Therefore recognition of the prevailing phosphine-resistant genotypes in a region is important to direct the management tactics to be adopted.