新分离Microbacterium sp．XT11菌产黄原胶降解酶生产条件的优化研究

新分离Microbacterium sp．XT11菌能够合成黄原胶降解酶,将植物病原菌野油菜黄单孢菌分泌的毒素因子黄原胶分解,生成具有激发子和抗微生物活性的黄原胶寡糖。实验确认,黄原胶和酵母浸粉分别是XT11菌生产黄原胶降解酶的最适碳源和氮源,获得最高酶活力的最低碳源和氮源浓度均为0.3％。XT11菌生产黄原胶降解酶的最适条件为：培养温度28℃,培养基起始pH7.0,转速150r／min。     

黄原胶寡糖生物活性的研究

利用黄原胶降解菌Cellulom onassp.XT11生产的黄原胶降解酶,对黄原胶进行生物降解,生产具有不同粘度/还原末端比的黄原胶寡糖,并研究了黄原胶寡糖在清除羟基自由基、植物防卫反应中激活因子活性和对植物病原菌抑制能力等方面的生物活性,结果表明黄原胶寡糖具有清除羟基自由基能力,并能激活植物防卫系统以抵御病原菌的侵染,同时对野油菜黄单孢菌也具有抑菌活性。     

黄原胶降解菌的筛选及其降解酶性质的研究

从野外采集并筛选到一株能降解黄原胶的菌株,并对菌种进行了对照鉴定。此外,对菌株的发酵参数、黄原胶降解酶的性质(最适反应温度、pH值,金属离子的影响、底物专一性、动力学研究等)作了初步的研究。结果显示,该酶的最适催化反应温度和pH分别为30℃～40℃和5．0～7．0;能够专一性降解黄原胶;测试大多数金属离子对酶活力没有明显影响,但Ca^2 能很大程度地缓解EDTA对酶活的抑制作用。     

黄原胶降解菌的筛选及其降解酶性质的研究*

从野外采集并筛选到一株能降解黄原胶的菌株,并对菌种进行了对照鉴定。此外,对菌株的发酵参数、黄原胶降解酶的性质(最适反应温度、pH值,金属离子的影响、底物专一性、动力学研究等)作了初步的研究。结果显示,该酶的最适催化反应温度和pH分别为30℃～40℃和5.0～7.0;能够专一性降解黄原胶;测试大多数金属离子对酶活力没有明显影响,但Ca²⁺能很大程度地缓解EDTA对酶活的抑制作用。     

基于差异基因表达谱的Microbacterium sp. XT11降解黄原胶潜能挖掘

为挖掘微杆菌(Microbacterium sp.)XT11在黄原胶降解过程中起关键作用的功能基因,预测黄原胶降解通路,利用转录组测序技术对该菌株在不同碳源培养条件下的转录本进行测序,对差异基因进行功能富集分析。结果表明,菌株XT11以葡萄糖为对照组,以黄原胶为碳源时可获得上调差异基因213个。显著上调的基因主要富集在聚糖降解、淀粉和蔗糖代谢途径、ABC转运、苯丙氨酸代谢、丙酮酸代谢五个KEGG途径。碳水化合物活性酶(Carbohydrate-active enzymes, CAZymes)功能注释表明,位于同一基因簇上的4个CAZymes基因和黄原胶降解直接相关,其余的CAZymes基因具有潜在的黄原胶降解活性。此外,预测到磷酸转移酶系统(phosphotransferase system, PTS)和ABC转运途径(ABC transporters)参与了胞外黄原胶降解中间产物的跨膜转运。挖掘了菌株XT11中黄原胶降解过程中的功能基因,并阐述了菌株XT11的黄原胶降解通路。     

黄原胶降解菌BIT-BJ001培养条件的优化

黄原胶在采油工程中有重要的应用,但其难降解性质给采油工程带来很多问题。从塔里木油田胡杨木根部样品中分离得到1株黄原胶降解菌BIT-BJ001,对其发酵条件的研究表明,此黄原胶降解菌最适培养条件为:黄原胶0.3%,酵母粉0.5%,Na+浓度0.8%,Mg2+浓度0.8%,初始pH值为10,温度60℃。菌种BIT-BJ001降解黄原胶的能力与发酵时间、发酵液中还原糖浓度有关,发酵96 h,黄原胶降粘率达到最高,发酵液中还原糖浓度过高,将抑制菌株对黄原胶的降解。     

黄原胶(Xanthan Gum)的特性、生产及应用

黄原胶是野油菜黄单孢菌分泌于胞外的中性水溶性多糖。由于其独特的流变性质而有着极其广泛的工业应用。介绍了黄原胶的生产、特性、降解以及应用,并对其应用潜力作了预测。     

黄原胶生产菌无色素黄单胞菌的选育和发酵条件的研究

从实验室保存菌株黄原胶生产菌野油菜黄单胞菌XG30-1出发,经亚硝基胍诱变,筛选到一株不产生黄色素的突变菌株XG30-1-SW,发酵产物的红外吸收图谱鉴定与出发菌株一致。该菌株以葡萄糖或蔗糖为碳源、大豆粉或大豆分离蛋白为氮源、pH7．0为最适发酵条件,产量最高可达33g/L,连续多次传代后突变性状能稳定遗传。     

黄原胶(Xanthan Gum)的特性、生产及应用*

黄原胶是野油菜黄单孢菌分泌于胞外的中性水溶性多糖。由于其独特的流变性质而有着极其广泛的工业应用。介绍了黄原胶的生产、特性、降解以及应用,并对其应用潜力作了预测。     

黄原胶降解的研究进展

综述了黄原胶的理化特性、降解意义及降解方法,重点介绍了生物法降解黄原胶的国内外研究进展,并对降解黄原胶的研究方向提出了寻求更多降解途径、开发寡糖产品等建议.     

Isolation and characterization of a xanthan-degrading Microbacterium sp. strain XT11 from garden soil

AIMS: Isolation and characterization of the xanthan-degrading Microbacterium sp. XT11. METHODS AND RESULTS: The bacterial isolate XT11, capable of fragmenting xanthan, has been isolated from soil sample. Morphological and biochemical analyses, as well as 16S rRNA gene sequence comparisons, demonstrated that strain XT11 should be grouped in the genus Microbacterium, and represented a new member in this family. Xanthan could be degraded by the xanthan-degrading enzyme released from strain XT11. It has been shown that xantho-oligosaccharides fragmented from xanthan had both elicitor activity and antibacterial effect against Xanthomonas campestris pv. campestris. CONCLUSIONS: The xanthan-degrading enzyme produced by the newly isolated XT11 could fragment xanthan to form oligosaccharides. SIGNIFICANCE AND IMPACT OF THE STUDY: Xanthan-degrading products would be useful for potential application in the control of black rot of cruciferous plants caused by X. campestris pv. campestris and, as an oligosaccharide elicitor, in making these plants resistant to disease.     

A pyruvated mannose-specific xanthan lyase involved in xanthan degradation by Paenibacillus alginolyticus XL-1.

The xanthan-degrading bacterium Paenibacillus alginolyticus XL-1, isolated from soil, degrades approximately 28% of the xanthan molecule and appears to leave the backbone intact. Several xanthan-degrading enzymes were excreted during growth on xanthan, including xanthan lyase. Xanthan lyase production was induced by xanthan and inhibited by glucose and low-molecular-weight enzymatic degradation products from xanthan. A xanthan lyase with a molecular mass of 85 kDa and a pI of 7.9 was purified and characterized. The enzyme is specific for pyruvated mannosyl side chain residues and optimally active at pH 6.0 and 55 degrees C.     

Biodegradation of xanthan by salt-tolerant aerobic microorganisms

Summary Three salt-tolerant bacteria which degraded xanthan were isolated from various water and soil samples collected from New Jersey, Illinois, and Louisiana. The mixed culture, HD1, contained aBacillus sp. which produced an inducible enzyme(s) having the highest extracellular xanthan-degrading activity found. Xanthan alone induced the observed xanthan-degrading activity. The optimum pH and temperature for cell growth were 5–7 and 30–35°C, respectively. The optimum temperature for activity of the xanthan-degrading enzyme(s) was 35–45°C, slightly higher than the optimum growth temperature. With a cell-free enzyme preparation, the optimum pH for the reduction of solution viscosity and for the release of reducing sugar groups were different (5 and 6, respectively), suggesting the involvement of more than one enzyme for these two reactions. Products of enzymatic xanthan degradation were identified as glucose, glucuronic acid, mannose, pyruvated mannose, acetylated mannose and unidentified oligo- and polysaccharides. The weight average molecular weight of xanthan samples shifted from 6.5·10⁶ down to 6.0·10⁴ during 18 h of incubation with the cell-free crude enzymes. The activity of the xanthan-degrading enzyme(s) was not influenced by the presence or absence of air or by the presence of Na₂S₂O₄ and low levels of biocides such as formaldehyde (25 ppm) and 2,2-dibromo-3-nitrilopropionamide (10 ppm). Formaldehyde at 50 ppm effectively inhibited growth of the xanthan degraders.     

A Pyruvated Mannose-Specific Xanthan Lyase Involved in Xanthan Degradation by Paenibacillus alginolyticus XL-1

The xanthan-degrading bacterium Paenibacillus alginolyticus XL-1, isolated from soil, degrades approximately 28% of the xanthan molecule and appears to leave the backbone intact. Several xanthan-degrading enzymes were excreted during growth on xanthan, including xanthan lyase. Xanthan lyase production was induced by xanthan and inhibited by glucose and low-molecular-weight enzymatic degradation products from xanthan. A xanthan lyase with a molecular mass of 85 kDa and a pI of 7.9 was purified and characterized. The enzyme is specific for pyruvated mannosyl side chain residues and optimally active at pH 6.0 and 55°C.     

Xanthan production by Xanthomonas campestris using whey permeate medium

Xanthan gum is a polysaccharide that is widely used as stabilizer and thickener with many industrial applications in food industry. Our aim was to estimate the ability of Xanthomonas campestris ATCC 13951 for the production of xanthan gum by using whey as a growth medium, a by-product of dairy industry. X. campestris ATCC 13951 has been studied in batch cultures using a complex medium for the determination of the optimal concentration of glucose, galactose and lactose. In addition, whey was used under various treatment procedures (de-proteinated, partially hydrolyzed by β-lactamase and partially hydrolyzed and de-proteinated) as culture medium, to study the production of xanthan in a 2 l bioreactor with constant stirring and aeration. A production of 28 g/l was obtained when partially hydrolysed β-lactamase was used, which proved to be one of the highest xanthan gum production reported so far. At the same time, an effort has been made for the control and selection of the most appropriate procedure for the preservation of the strain and its use as inoculant in batch cultures, without loss of its viability and its capability of xanthan gum production. The pre-treatment of whey (whey permeate medium hydrolyzed, WPH) was very important for the production of xanthan by the strain X. campestris ATCC 13951 during batch culture conditions in a 2 l bioreactor. Preservation methods such as lyophilization, cryopreservation at various glycerol solution and temperatures have been examined. The results indicated that the best preservation method for the producing strain X. campestris ATCC 13951 was the lyophilization. Taking into account that whey permeate is a low cost by-product of the dairy industry, the production of xanthan achieved under the studied conditions was considered very promising for industrial application.     

Biodegradation of xanthan by newly isolated Cellulomonas sp. LX, releasing elicitor-active xantho-oligosaccharides-induced phytoalexin synthesis in soybean cotyledons

A Cellulomonas sp. LX newly isolated from soil samples could degrade the extracellular polysaccharide (xanthan) of Xanthomonas campestris. Such degradation was inhibited by glucose addition. Xanthan-degrading enzyme activity was found in the culture supernatant when Cellulomonas sp. LX was grown in the medium with xanthan as carbon source. The optimal pH and temperature for the xanthan-degrading reaction was 6.0 and 40 °C, respectively. The bioactivity of the xantho-oligosaccharide was examined with the soybean cotyledon bioassay and found it was an active elicitor.     

Genetic and physical analyses of a cluster of genes essential for xanthan gum biosynthesis in Xanthomonas campestris.

Xanthomonas campestris produces copious amounts of a complex exopolysaccharide, xanthan gum. Nonmucoid mutants, defective in synthesis of xanthan polysaccharide, were isolated after nitrosoguanidine mutagenesis. To isolate genes essential for xanthan polysaccharide synthesis (xps), a genomic library of X. campestris DNA, partially digested with SalI and ligated into the broad-host-range cloning vector pRK293, was constructed in Escherichia coli. The pooled clone bank was conjugated en masse from E. coli into three nonmucoid mutants by using pRK2013, which provides plasmid transfer functions. Kanamycin-resistant exconjugants were then screened for the ability to form mucoid colonies. Analysis of plasmids from several mucoid exconjugants indicated that overlapping segments of DNA had been cloned. These plasmids were tested for complementation of eight additional nonmucoid mutants. A 22-kilobase (kb) region of DNA was defined physically by restriction enzyme analysis and genetically by ability to restore mucoid phenotype to 10 of the 11 nonmucoid mutants tested. This region was further defined by subcloning and by transposon mutagenesis with mini-Mu(Tetr), with subsequent analysis of genetic complementation of nonmucoid mutants. A region of 13.5 kb of DNA was determined to contain at least five complementation groups. The effect of plasmids containing cloned xps genes on xanthan gum synthesis was evaluated. One plasmid, pCHC3, containing a 12.4-kb insert and at least four linked xanthan biosynthetic genes, increased the production of xanthan gum by 10% and increased the extent of pyruvylation of the xanthan side chains by about 45%. This indicates that a gene affecting pyruvylation of xanthan gum is linked to this cluster of xps genes.     

Isolation of a Xanthomonas campestris strain with elevated beta-galactosidase activity for direct use of lactose in xanthan gum production

AIMS: To isolate a Xanthomonas campestris strain that can use lactose directly for xanthan gum production. METHODS AND RESULTS: The presence of indigenous beta-galactosidase gene in the wild-type Xc17 was detected by PCR and Southern hybridization. Treatment of Xc17 with nitrous acid resulted in the isolation of Xc17L with a 3.5-fold elevation of beta-galactosidase activity capable of growing in lactose-based medium. Xc17L is stable for at least 100 generations in terms of beta-galactosidase expression. The amounts of xanthan produced by Xc17L in lactose-based medium are comparable to those in glucose-based medium. CONCLUSIONS: Xc17L is potentially useful for xanthan production from whey, a waste containing lactose. SIGNIFICANCE AND IMPACT OF THE STUDY: A lactose-utilizing strain of X. campestris strain can be constructed without incorporation of any exotic DNA or antibiotic resistance gene and therefore concern of a gene-modified organism and fear of a spread of an antibiotic-resistant gene are avoided.