Evaluation of the selective respiratory inhibition method for measuring the ratio of fungal:bacterial activity in acid agricultural soils

A procedure for the measurement of the fungal and bacterial contribution to substrate-induced respiration was tested in three arable soils. Glucose and different amounts of cycloheximide (eukaryote inhibitor) and streptomycin sulfate (prokaryote inhibitor) were added to soil suspensions, and respiration (CO₂ evolution) was measured. Streptomycin sulfate concentrations from 10 to 120 mg ml^–1 soil solution caused a stable inhibition of respiration. Amounts of cycloheximide ranging from 5 to 35 mg ml^–1 showed an increasing inhibition. In a test with separate and combined addition of the antibiotics at maximum inhibitory concentrations, inhibition by streptomycin was completely overlapped by cycloheximide. This indicated non-target inhibition which may lead to overestimation of fungal respiration. Experiments with sterilized soils inoculated with either fungi or bacteria confirmed that streptomycin selectively inhibited bacteria. Cycloheximide, however, did not only inhibit fungal respiration already at 2 mg ml^–1, but also increasingly inhibited bacterial respiration at increasing concentrations. Only at less than 5 mg cycloheximide ml^–1 was the condition of selective fungal inhibition fulfilled. When 2 mg cycloheximide and 10 mg streptomycin sulfate ml^–1 were applied, the sum of the separate inhibitions almost equalled the combined inhibition by the mix of both inhibitors in field samples. This method yielded fungal:bacterial respiration ratios of 0.50 to 0.60, and confirmed the dominance of bacteria in Dutch arable soils. The ratios obtained by the selective inhibitors were not correlated with, and were higher than, ratios of fungal:bacterial biovolume (0.19 to 0.46) as determined by microscopy and image analysis. Similar measurements in a forest soil (A-horizon) raised doubts on the reliability of the fungal inhibition by cycloheximide in this soil. It is concluded that the separate:combined inhibition ratio should always be checked, and comparison with other approaches is recommended. Received: 17 September 1996     

患红底板症的中华鳖幼鳖的病原菌分离与鉴定

【目的]为中华鳖红底板病病原鉴定和防治提供参考依据。[方法]从患红底板症的中华鳖幼鳖的血、心、肝、脾、肠等组织中分离病原菌,并进行形态学观察、16SrDNA序列分析鉴定及药敏试验。[结果]从中华鳖中分离到2株细菌,分别为嗜水气单胞菌（Aeromonas hydrophila）和格氏乳球菌（Lactococcus garviae）。人工感染试验结果表明2株分离菌对中华鳖都有致病性;用含有抗生素的20种药敏纸片进行药敏试验,发现该株嗜水气单胞菌对复达欣高敏,对呋喃妥因中敏,对其他18种药物耐药;该株格氏乳球菌对复达欣、万古霉素、呋喃妥因、妥布霉素、头孢唑啉等5种高敏,对庆大霉素、卡那霉素、头孢西丁等3种中敏,而其他13种药物耐药。[结论]从中华鳖幼鳖中分离的2株细菌具有较强的致病性和耐药性。     

Survey on the prevalence of diarrhoea in pre-weaning piglets and on feeding systems as contributing risk factors in smallholdings in Central Vietnam

A cross-sectional survey on the prevalence of diarrhoea in pre-weaning piglets, and on management and feeding systems under farm conditions was carried out in Thua Thien Hue Province. Faecal samples were collected from 63 piglets without, and 90 piglets with diarrhoea to determine the occurrence of Salmonella, Escherichia coli (E. coli) and different E. coli antigens (K88, K99 and 987P). The prevalence of diarrhoea was higher in the rainy season than in the dry season (33% vs 18%) and the results indicated differences in prevalence between areas. Salmonella and E. coli were found to the same extent in faeces from piglets without and with diarrhoea. All E. coli antigens were isolated from piglets without and with diarrhoea. However, the frequency was much higher in piglets suffering from diarrhoea. In piglets with diarrhoea antigen K88 was found in 26% and 20% of the samples, antigen K99 in 37% and 24% of the samples, and antigen 987P in 31% and 32% of the samples collected in the dry and rainy seasons, respectively. Nutrient supply for sows and for piglets was low in comparison with feeding standards, which may be a contributory factor to the high incidence of diarrhoea in piglets. Thus, the nutrition of sows as well as piglets could be important components in the aetiology of the disease and needs to be studied further.     

Molecular and serological diagnosis of Bartonella infection in 61 dogs from the United States

Background: Molecular diagnosis of canine bartonellosis can be extremely challenging and often requires the use of an enrichment culture approach followed by PCR amplification of bacterial DNA. Hypotheses: (1) The use of enrichment culture with PCR will increase molecular detection of bacteremia and will expand the diversity of Bartonella species detected. (2) Serological testing for Bartonella henselae and Bartonella vinsonii subsp. berkhoffii does not correlate with documentation of bacteremia. Animals: Between 2003 and 2009, 924 samples from 663 dogs were submitted to the North Carolina State University, College of Veterinary Medicine, Vector Borne Diseases Diagnostic Laboratory for diagnostic testing with the Bartonellaα‐Proteobacteria growth medium (BAPGM) platform. Test results and medical records of those dogs were retrospectively reviewed. Methods: PCR amplification of Bartonella sp. DNA after extraction from patient samples was compared with PCR after BAPGM enrichment culture. Indirect immunofluorescent antibody assays, used to detect B. henselae and B. vinsonii subsp. berkhoffii antibodies, were compared with PCR. Results: Sixty‐one of 663 dogs were culture positive or had Bartonella DNA detected by PCR, including B. henselae (30/61), B. vinsonii subsp. berkhoffii (17/61), Bartonella koehlerae (7/61), Bartonella volans‐like (2/61), and Bartonella bovis (2/61). Coinfection with more than 1 Bartonella sp. was documented in 9/61 dogs. BAPGM culture was required for PCR detection in 32/61 cases. Only 7/19 and 4/10 infected dogs tested by IFA were B. henselae and B. vinsonii subsp. berkhoffii seroreactive, respectively. Conclusions and Clinical Importance: Dogs were most often infected with B. henselae or B. vinsonii subsp. berkhoffii based on PCR and enrichment culture, coinfection was documented, and various Bartonella species were identified. Most infected dogs did not have detectable Bartonella antibodies.     

植物内生菌研究发展现状

植物内生细菌在各领域都有广泛的应用价值,如促进植物生长、抗病虫害、生物固氮、降解有毒害化合物等方面都引人关注.本文概述了内生细菌侵染定殖规律及其定殖的检测方法,内生细菌研究应用过程中存在的问题,展望了内生细菌的应用过程.     

松材线虫携带细菌产生抑制真菌的物质

研究发现松材线虫携带的两株荧光假单胞菌GcM5-1A、ZM4A和恶臭假单胞菌ZpB1-2A具有抑制真菌菌丝生长的作用.首先对供试的8个细菌菌株进行抑菌活性生物测定,从中筛选出3个具有抑菌活性的细菌菌株;接着对细菌培养液及滤液、死细菌及活细菌进行生物测定;最后对细菌代谢物的性质进行生物测定.实验证明抑制真菌菌丝生长的活性成分为松材线虫携带细菌的挥发性代谢产物.     

Changes in soil fungal:bacterial biomass ratios following reductions in the intensity of management of an upland grassland

In this study we examined the effect on soil fungal:bacterial biomass ratios of withholding fertiliser, lime, and sheep-grazing from reseeded upland grassland. The cessation of fertiliser applications on limed and grazed grassland resulted in a reduction in soil pH from 5.4 to 5.1. The cessation of fertiliser applications and liming on grazed grassland resulted in a fall in pH from 5.4 to 4.7, whereas withholding fertiliser and lime and the removal of grazing resulted in a further reduction to pH 4.5. Substrate-induced respiration was reduced in the unfertilised grazed (21%; P<0.01) and unfertilised ungrazed (36%; P<0.001) treatments. Bacterial substrate-induced respiration and bacterial fatty acids were unaffected by the treatments. The relative abundance of the fungal fatty acid 18:26 increased by 39 and 72% (P<0.05) in the limed grazed and unfertilised grazed treatments, respectively. Fungal substrate-induced respiration increased in the limed grazed (18%) and unfertilised grazed (65%; P<0.05) treatments. The ratio of 18:26: bacterial fatty acids was correlated with the ratio of fungal:bacterial substrate-induced respiration (r=0.69; P<0.001).     

中国对虾细菌性黑鳃病的组织病理观察

报道中国对虾细菌性黑鳃病的症状、鳃组织的显微、超显微结构的病理变化。病虾鳃区呈，黑色条斑状、活动力差、厌食、死亡率较高。不镜下观察，鳃组织严重坏死、断裂，鳃丝充血，为多量血淋巴细胞浸润，黑色素在多沉积在鳃丝末端。电锐观察到鳃组织的甲壳层和表皮层中的许多没切面的杆状细菌，呈多形态，大小约为（０．２－０．４）×（１．２－１．８微米，单个，偶而连成双，无芽孢，菌体周围细胞结构完全瓦解，组织被腐蚀或许多圆     

白蚁肠道内的共生微生物区系

白蚁是少数几种以木质纤维素类物质为食的动物之一,在自然界木质纤维素循环中担当重要角色,并可为木质纤维素转化为生物燃料提供生化催化剂。白蚁的后肠内包含有密集的和种类丰富的微生物,这些微生物可降解纤维素和半纤维素、发酵成短链的脂肪酸、脂肪酸被白蚁吸收,它们主要有原生动物(低等白蚁)、细菌、真菌等。综述了白蚁肠道内共生微生物与宿主的共生关系及其微生物的应用前景。     

近十年我国耐重金属细菌研究文献分析

细菌作为微生物中的最大群体,在重金属耐性研究领域拥有其他物种所不具有的特点。研究耐重金属细菌具有重要的理论意义和生产应用价值。基于CNKI中国期刊全文数据库,采用文献计量学的方法对我国近十年（2000-2010年）细菌重金属耐性文献进行统计分析,为了解和把握该领域研究的热点和发展趋势提供依据。