The effect of temperature on survival of pathogenic bacteria in biogas plants

The paper deals with the hygienic advantages of sanitation to treat dairy manure in full‐scale biogas plants. The slurry samples were collected from two thermophilic biogas plants (55°C) and two mesophilic biogas plants (38°C) in Hokkaido Japan. A detectable number of Coli‐aerogenes group and Enterococcus in the slurries after anaerobic digestion (AD) could not be found in either thermophilic biogas plants. However, in both mesophilic biogas plants the viable numbers of Coli‐aerogenes group and Enterococcus were detected in the slurries even after anaerobic digestion. The mean decimation reduction time (T₉₀) values of the Coli‐aerogenes group and Enterococcus in the slurries during mesophilic digestion were 13.3 days and 16.7 days, respectively.     

The survival of multidrug‐resistant bacteria in thermophilic and mesophilic anaerobic co‐digestion of dairy manure and waste milk

Anaerobic digestion is considered as a promising method to manage animal waste with antibiotic‐resistant bacteria. Current research was conducted to investigate the survival of multidrug‐resistant bacteria (MDRB) resistant to three groups of antibiotics: (i) cefazolin, neomycin, vancomycin, kanamycin (group 1); (ii) penicillin, oxytetracycline, ampicillin, streptomycin (group 2); and (iii) cefazolin, neomycin, vancomycin, kanamycin, penicillin, oxytetracycline, ampicillin, streptomycin (group 3), in anaerobic digestion of dairy manure and co‐digestion of dairy manure and waste milk at 37°C and 55°C for 22 days, respectively. The population densities of three groups of MDRB on peptone, tryptone, yeast and glucose agar plates incubated at 30°C for 7 days before and after digestion showed 100% destruction in both digestates at thermophilic temperature. Overall reduction of more than 90% of three groups of MDRB was observed in mesophilic digestion with no significant differences (P > 0.05) between manure and milk mixture. Co‐digestion of dairy manure and waste milk always produced significantly (P < 0.05) higher total gas and methane gas than digestion of manure alone at both temperatures. Gas production in each case was significantly (P < 0.05) higher in thermophilic digestion than in mesophilic digestion. The results demonstrate that thermophilic co‐digestion of dairy manure and waste milk offers more benefits in terms of the environment and economy.     

Effect of solid–liquid separation on anaerobic digestion of dairy manure in semi‐continuous stirred tank reactors: Process performance and digestate characteristics

The objective of this study was to investigate the effect of solid–liquid separation on anaerobic digestion of dairy manure in semi‐continuous stirred tank reactors. Reactors fed with liquid fraction of dairy manure (screened liquid manure) were kept in water baths at mesophilic (Run 1) and thermophilic (Run 3) temperatures, respectively, while reactors fed with water diluted manure and kept at mesophilic (Run 2) and thermophilic (Run 4) temperatures as control reactors. The performances of reactors were compared in terms of biogas and methane production, and digestate characteristics. The methane yields obtained from screened manure were higher than those from diluted manure at both mesophilic and thermophilic temperatures, while the highest methane yield was 185 L/kg VS_added under thermophilic temperature. Solid–liquid separation also had improved the effect on digestate fertilizer characteristics. Among four digestates from reactors, the highest contents of nutrients, N (4.12 g/kg) and P (2.36 g/kg) were found in Run 3, while the highest content of K (3.42 g/kg) was found in Run 1. These results showed the benefits of solid–liquid separation of dairy manure on process performance and digestate characteristics.     

东祁连山高寒草地几种禾本科牧草根际促生菌研究

本研究以东祁连山高寒草地常见的7种禾本科牧草为材料,通过分离培养的方法研究了其根际细菌的数量和分布,重点研究了其有固氮作用的细菌数量和分布。结果发现,7种植物根际均存在大量的细菌,总数在2.50×10⁶~17.07×10⁶ cfu/g,不同植物根际细菌的数量和分布不同,以高原早熟禾根际细菌数量最多,冰草和赖草根际细菌最少,其余禾草居中;根际固氮菌的数量和分布也因牧草种类不同而不同。7种供试植物根际分离到固氮菌201株。且细菌和PGPR菌株的数量均呈现“根系表面(RP)>根际土壤(RS)>根内(HP)”的分布趋势,表现出强烈的根际效应。     

Potential of anaerobic digestate of dairy manure in suppressing soil‐borne plant disease

Frequent use of pesticides to control soil‐borne plant disease leads to environmental pollution and the development of pesticide resistance in phytopathogens. Soil amendment is considered to have the potential of suppressing plant disease because of its biological properties. However, information on anaerobic digestate is limited. In this study, potential of antagonistic activities of anaerobic digestate against phytopathogens were investigated by detecting the amounts of antagonistic bacteria (Bacillus and Pseudomonas) in anaerobic digestates of dairy manure. The results showed that anaerobic digestion increased the total amounts of Bacillus and Pseudomonas in digestate. Bacillus suppressed growth of phytopathogens, while Pseudomonas did not show any antagonistic activities. These results indicated that Bacillus was an effective antagonistic bacterium in digestate against phytopathogens. Furthermore, two selected isolates, B11 (Bacillus subtilis) and B59 (Bacillus licheniformis), were applied in field experiments and showed significant reduction in percent infection of potato late blight (Phytophthora infestans). These results demonstrate the benefits of digestate in suppressing soil‐borne plant diseases caused by antagonistic bacteria.     

黄芪根际促生菌(PGPR)筛选与特性研究

为获得黄芪根际PGPR菌株并明确其促生特性,可为其在生产中的应用提供依据,本研究以黄芪的根瘤、根系及根际土壤为材料,利用选择性培养基分离筛选根瘤菌与溶磷菌,测定根瘤菌固氮酶活性、溶磷菌株的溶磷能力及分泌3-吲哚乙酸(IAA)的能力,从中筛选出综合性能优良的菌株,并运用生理生化鉴定和16S rDNA分子生物学鉴定相结合的方法鉴定优良菌株的种属。结果发现,溶磷菌数量的分布具有根系表面(RP)>根表土壤(RS)>远根土(NRS)>根内(HP)的规律,有明显的根际效应;经分离纯化获得76 株PGPR菌,其中根瘤菌1株、溶解无机磷菌株42 株和溶解有机磷菌株33 株,其中可分泌IAA能力的溶磷菌株有7株;筛选出综合性能优良,有进一步开发应用潜力的溶磷菌株7株,根瘤菌1株,经鉴定溶磷菌中3株为Pseudomonas sp.,3株为Bacillus sp.和1株为Klebsiella oxytoca,根瘤菌为Rhizobium sp.,这为研制生物菌肥提供优良菌种,同时丰富优良根际促生菌资源库。     

根际促生菌的筛选及其在尾矿改良中的应用

为探索经济高效且应用推广性强的尾矿改良和植被恢复措施,筛选了来自尾矿原生植被的根际促生菌,并将其组配形成混合促生菌液。采用盆栽试验,研究了混合促生菌液（B）、生物炭（C）和粪肥（F）及不同组合（BC、BF、CF、BⅠCF、BⅡCF,其中BⅠCF是三者复合处理;BⅡCF是在BⅠCF基础上增加1倍的混合促生菌液）对千叶蓍种子萌发和植株生长,根际微生物群落组成,矿砂养分、酶活性以及盆栽系统中的氮素转移和可利用磷、钾总量的影响。筛选得到4株具有固氮、溶磷、解钾、合成吲哚乙酸或分泌1-氨基环丙烷羧酸脱氨酶的根际促生菌,分别为KSB1、KSB2、KSB7和KSB21。盆栽试验结果表明：与CK（空白对照）相比,接种混合促生菌能够强化矿砂磷酸酶活性,并提高假单胞菌属和根瘤菌属在根际环境中的丰度;添加生物炭对矿砂养分和千叶蓍生长的影响有限;施用粪肥可促进千叶蓍生长,强化矿砂酶活性,显著提高蓝细菌属丰度（P<0.01）、盆栽系统氮素总量及可利用磷、钾总量。与单独施用粪肥（F）相比,接种混合促生菌+粪肥（BF）与添加生物炭+粪肥（CF）均能进一步提高部分千叶蓍生长指标和矿砂酶活性。此外,BF处理盆栽系统氮素总量增加了11.18%,可利用磷、钾总量分别增加了22.54%和22.00%;而CF仅有可利用钾总量增加了8.32%。BⅠCF和BⅡCF处理下各指标均高于其他处理,BⅡCF矿砂碱解氮、磷酸酶活性以及千叶蓍植株生物量等指标较BⅠCF有显著提高（P<0.05）,且盆栽系统氮素总量增加了9.54%,千叶蓍植株钾总量增加了19.12%,蓝细菌属和假单胞菌属的相对丰度提高了51.96%和13.62%。试验条件下,直接接种促生菌或添加生物炭对尾矿基质改良和植被恢复效果不显著;施用粪肥对改善矿砂养分供给和促进绿垦作物千叶蓍的生长有关键作用;促生菌液和生物炭的功能发挥与粪肥的施用与否存在直接关系;BⅡCF处理是一种有效的矿砂改良措施,其中的多功能混合促生菌发挥了固氮、溶磷和解钾作用,并增强了千叶蓍对钾元素的吸收利用能力。     

岷山红三叶根际优良促生菌对其宿主生长和品质的影响

从岷山红三叶根际分离出高效溶磷菌,并对其分泌生长激素、拮抗病原菌特性进行测定,筛选出优良促生菌6株,根瘤菌1株,按照一定比例混合制成复合菌肥,进行盆栽试验,研究复合菌肥对岷山红三叶产量、品质及异黄酮含量的影响。结果表明:利用筛选的优良促生菌和根瘤菌研制的复合微生物菌肥符合《微生物肥料》标准(NY227-94)。75%化肥+PGPR菌肥处理使岷山红三叶干草总产量较CK增加4.76%,同时,该处理可提高红三叶粗蛋白、粗灰分、钙、磷含量,降低中、酸性洗涤纤维含量;50%化肥+PGPR菌肥处理对岷山红三叶的总干草产量、营养品质以及4种异黄酮的含量均没有显著影响。