Biodelignification of wheat straw by different fungal associations

Seven strains of fungi were tested individually as well as in different combinations to determine their lignin degrading ability using wheat straw as natural substrate. When tested individuallyPhanerochaete chrysosporium caused a maximum loss in total organic matter (26.45%) as well as in the lignin component (28.93%). The associations between different groups: white-rot plus white-rot, white-rot plus brown-rot and white-rot plus soft-rot fungi revealed that in certain combinations the ligninolysis was enhanced to variable extent.Deadalea flavida plusP. chrysosporium was the best association to bring about a lignin loss of 36.27%.     

Genotypic differences in the uptake and distribution of radiocaesium in plants

The ability of endophytic bacteria to influence Erwinia carotovora var. atroseptica (Eca) growth and disease development was examined in potatoes. Bacterial populations isolated from within the tubers of five potato (Solanum tuberosum L.) cultivars (Kennebec, Butte, Green Mountain, Russet Burbank and Sebago) showed antibiosis toward Eca in an in vitro assay. Sebago was host to the highest percentage of bacterial isolates inhibiting Eca growth in vitro (49.5%), followed by Green Mountain (33.3%), Kennebec (29.3%), Russet Burbank (12.9%) and Butte (1.8%). Of these, Curtobacterium luteum was the most common species. Few endophytic bacteria from Butte were inhibitory to Erwinia; all were from Pantoea agglomerans. Significantly higher populations of Erwinia-inhibiting bacteria were recovered from Kennebec (1.89 × 10⁶ cfu fresh weight tuber tissue) as compared to the other cultivars; the lowest populations were recovered from Butte (0.01 × 10⁶ cfu per g fresh weight tuber tissue). Published levels of cultivar disease resistance to blackleg did not correspond to actual bacterial soft rot development (induced by Eca) in an in vivo (tuber) assay. However, bacterial soft rot development was negatively correlated with the density of tuber populations of endophytic bacteria found able to inhibit Eca growth in vitro (R=−0.879, p=0.05).     

Identification by Tn-seq of Dickeya dadantii genes required for survival in chicory plants

The identification of the virulence factors of plant-pathogenic bacteria has relied on the testing of individual mutants on plants, a time-consuming process. Transposon sequencing (Tn-seq) is a very powerful method for the identification of the genes required for bacterial growth in their host. We used this method in a soft-rot pathogenic bacterium to identify the genes required for the multiplication of Dickeya dadantii in chicory. About 100 genes were identified showing decreased or increased fitness in the plant. Most had no previously attributed role in plant–bacterium interactions. Following our screening, in planta competition assays confirmed that the uridine monophosphate biosynthesis pathway and the purine biosynthesis pathway were essential to the survival of D. dadantii in the plant, as the mutants ∆carA, ∆purF, ∆purL, ∆guaB and ∆pyrE were unable to survive in the plant in contrast with the wild-type (WT) bacterium. This study also demonstrated that the biosynthetic pathways of leucine, cysteine and lysine were essential for bacterial survival in the plant and that RsmC and GcpA were important in the regulation of the infection process, as the mutants ∆rsmC and ∆gcpA were hypervirulent. Finally, our study showed that D. dadantii flagellin was glycosylated and that this modification conferred fitness to the bacterium during plant infection. Assay by this method of the large collections of environmental pathogenic strains now available will allow an easy and rapid identification of new virulence factors.     

Chemotactic response of Ginseng bacterial soft-rot to Ginseng root exudates

Our purpose was to evaluate chemotactic response of Ginseng bacterial soft-rot to ginseng root exudates. The exudates of plant roots has a significant influence on the population changes of rhizosphere microorganisms and chemotaxis is an important way in which many pathogens sense the signals of host plants and invade the host plants. In this study, with the capillary method, we tested the chemotactic responses of Ginseng bacterial soft-rot for three ginseng roots exudates under four chemotactic parameters (concentration, temperature, pH and time). The results showed that the chemotatic response of the Ginseng bacterial soft-rot for the ginseng roots exudates at the water layer where pH = 7 and the concentration was 0.0125 mg/L reached its peak value under the circumstance that the exudates was cultivated for 60 min at 25 °C. The chemotatic ratios were respectively 124.89% and 89.44%. For the butanol extract layer and the petroleum ether faction at the concentration of 0.125 mg/L and the pH value at 7, the ginseng roots exudatess reached peak values at 25 °C and 30 °C and 60 min and 75 min respectively, and the chemotatic ratios were respectively 139.64% and101.87%, and 115.29% and 81.36%. The three ginseng roots exudates had positive effects for the chemotaxis of the Ginseng soft-rot bacteria, but the effect declined as the concentration increased.     

Genetic diversity of soft rot strains of Pectobacterium,isolated from different hosts,using ISSR marker

Pectobacteria are one of the most important groups of plant pathogenic bacteria and have been reported in many countries including Iran. Thirty-five Iranian strains of pectobacteria were isolated from potato, cabbage, sugar beet, pepper, carrot, onion, cucumber, turnip and tomato host plants cultivated in Fars province of Iran, in 2013. The genetic diversity among the strains was evaluated using ISSR marker. The tested strains were rod-shape, motile with peritrichous flagella, gram-negative, facultative anaerobes, oxidase-negative, catalase-positive, and were able to cause potato rot, while they could not induce hypersensitive reaction on tobacco leaves. Based on phenotypic criteria, the isolated strains were categorised into three groups. The strains of first, second and third groups were related to Pectobacterium carotovorum subsp. carotovorum, Pectobacterium betavascularum and Dickeya chrysanthemi, respectively. According to ISSR assay, the primers that used in this assay showed significant diversity among the strains and the specific primers GTGC4, GAGC4 and GTG5 confirmed the classification.     

Biodegradation of wood in crude oil-polluted soil

A field investigation (April–November) in Nigeria showed that biodegradation of obeche (Triplochiton scleroxylon) wood blocks was initially retarded in crude oil-contaminated soil but later became enhanced as indicated by loss of compression resistance. Further indication of this pattern was the detection of soft-rot cavities and basidiomycete fungi after 2–3 months exposure when compared to control blocks in uncontaminated soil. Laboratory tests with Pleurotus sp., Trametes sp., Gloeophyllum sp. (basidiomycetes) and Chaetomium sp. (soft-rot fungus) confirmed that degradation of crude oil-coated obeche blocks was markedly retarded without the presence of hydrocarbon-degrading bacteria. The filtrate of hydrocarbon-degrading Pseudomonas sp. grown in mineral salt/crude oil medium for 3–4 weeks supported growth of the test fungi better than in carboxymethyl cellulose medium but less than in potato dextrose broth. Similarly, wood blocks immersed in the filtrate became significantly more susceptible to fungal degradation. Pseudomonas sp. from stationary phase growth in crude oil medium depleted residual sugar in basidiomycete-degraded sawdust with a concomitant marked increase in its population. It may be concluded that readily metabolizable products of crude oil degradation by soil organisms and the removal of residual sugar which may have prevented catabolite repression of cellulases, culminated in increased attack on the wood by soil-borne wood-decomposing organisms.     

木材上的微生物类群对木材的分解及其演替规律

论述了木材上的微生物类群以及各类群在木材生物分解过程中的演替规律 ,并解释了活立木心材能够发生腐朽的原因。结果表明 :能够生长在木材上的微生物类群有木材腐朽菌、木材软腐菌、木材变色菌、污染性霉菌、细菌、放线菌等多种。这些微生物类群共同合作完成对复杂的木质有机物质的生物分解。它们按一定次序进行作用 ,在木材生物分解的不同时期显示出明显的菌种协调与演替规律。一般情况是细菌、一些半知菌、接合菌和子囊菌等先驱微生物首先侵入 ,然后草本对策的木材腐朽菌开始出现 ,最后由竞争对策或忍耐对策的木腐菌取代草本对策的木腐菌 ,这时木材的分解过程就进入稳定的发展阶段 ,最后使木材分解或腐朽。木材腐朽最终是腐殖化阶段 ,这时微生物群落被土壤习居菌如毛霉、青霉、木霉、镰刀菌及细菌与放线菌等所取代。