Virulence of ‘Dickeya solani’ and Dickeya dianthicola biovar‐1 and ‐7 strains on potato (Solanum tuberosum)

Studies were conducted to explain the relative success of ‘Dickeya solani’, a genetic clade of Dickeya biovar 3 and a blackleg‐causing organism that, after recent introduction, has spread rapidly in seed potato production in Europe to the extent that it is now more frequently detected than D. dianthicola. In vitro experiments showed that both species were motile, had comparable siderophore production and pectinolytic activity, and that there was no antagonism between them when growing. Both ‘D. solani’ and biovar 1 and biovar 7 of D. dianthicola rotted tuber tissue when inoculated at a low density of 10³ CFU mL^?1. In an agar overlay assay, D. dianthicola was susceptible to 80% of saprophytic bacteria isolated from tuber extracts, whereas ‘D. solani’ was susceptible to only 31%, suggesting that ‘D. solani’ could be a stronger competitor in the potato ecosystem. In greenhouse experiments at high temperatures (28°C), roots were more rapidly colonized by ‘D. solani’ than by biovar 1 or 7 of D. dianthicola and at 30 days after inoculation higher densities of ‘D. solani’ were found in stolons and progeny tubers. In co‐inoculated plants, fluorescent protein (GFP or DsRed)‐tagged ‘D. solani’ outcompeted D. dianthicola in plants grown from vacuum‐infiltrated tubers. In 3 years of field studies in the Netherlands with D. dianthicola and ‘D. solani’, disease incidence varied greatly annually and with strain. In summary, ‘D. solani’ possesses features which allow more efficient plant colonization than D. dianthicola at high temperatures. In temperate climates, however, tuber infections with ‘D. solani’ will not necessarily result in a higher disease incidence than infections with D. dianthicola, but latent seed infection could be more prevalent.     

2株分泌型铁载体真菌对番茄青枯病的防效

为筛选对番茄青枯病防治效果好的天然产物,本文以分泌型铁载体产生菌云南木霉Trichoderma yunnanense 2-14F2和拟球孢白僵菌Beauveria pseudobassiana 2-8F2为材料,考察其铁载体活性物质对番茄青枯病的防效。采用CAS检测法及全波段紫外光吸收法判定铁载体化学结构类型及其活性。采用Sephadex-LH20凝胶划段法分离活性物质。采用平板扩散及96孔板倍半稀释法检测铁载体活性物质对青枯雷尔氏菌Ralstonia solanacearum的离体抑菌活性;采用盆栽法检测活性物质对番茄青枯病的防效。结果显示,菌株2-14F2和2-8F2产铁载体活性单位(SU)分别为62.02%和52.06%,铁载体化学结构类型均为异羟肟酸盐型(hydroxamates)。当铁载体活性物质浓度为0.15 mg/mL时,两菌株对青枯雷尔氏菌抑菌率分别为73.26%(2-14F2)和37.23%(2-8F2);对番茄青枯病的防治效果分别达到51.36%(2-14F2)与50.27%(2-8F2)。此外,当两菌株铁载体活性物质中含1 mol/L FeCl₃     

Diversity of siderophore‐producing bacteria isolated from the intestinal tracts of fish along the Japanese coast

This study examined the diversity of siderophore‐producing bacteria in the intestinal tracts of coastal fish in Japan and screened candidate bacterial strains for probiotic use in aquaculture. Of the 2637 bacteria isolated from the 27 fish specimens (13 species) and six environmental samples collected in this study, 266 isolates exhibited the ability to produce siderophores. Siderophore producers were detected in the intestines of 18 of the fish specimens caught (68%) at densities of 2.3 × 10⁴–2.3 × 10⁸ CFU g^?1, in all three seawater samples at 2.0 × 10²–1.3 × 10³ CFU mL^?1 and in all three sand samples at 2.6 × 10¹–2.8 × 10⁴ CFU g^?1. These findings suggest that siderophore‐producing bacteria are widely distributed in the intestinal tracts of coastal fish and their environments. Analysis of 16S rRNA gene sequences revealed that the siderophore producers belonged to 38 species, of which Vibrio splendidus, Vibrio ichthyoenteri and Vibrio crassostreae accounted for 32.7%, 19.5% and 11.3% of the 266 isolates, respectively, suggesting that these bacteria are indigenous to the intestinal tract of coastal fish. Six bacterial species, Enterovibri norvegicus, Photobacterium leiognathi, Photobacterium phosphoreum, Photobacterium rosenbergii, V. crassostrea and Vibrio scophthalmi were identified as possible candidates for use as probionts in fish aquaculture.     

Renibacterium salmoninarum iron‐acquisition mechanisms and ASK cell line infection: Virulence and immune response

Renibacterium salmoninarum is the aetiological agent of bacterial kidney disease (BKD) in salmonid farms. This pathogen possesses at least three iron‐acquisition mechanisms, but the link between these mechanisms and virulence is unclear. Therefore, this study used RT‐qPCR to assess the effects of normal and iron‐limited conditions on iron‐uptake genes controlled by IdeR and related to iron acquisition in Chilean R. salmoninarum strain H‐2 and the type strain DSM20767^T. Further evaluated was the in vitro immune‐related response of the Atlantic Salmon Kidney (ASK) cell line, derived from the primary organ affected by BKD. R. salmoninarum grown under iron‐limited conditions overexpressed genes involved in haemin uptake and siderophore transport, with overexpression significantly higher in H‐2 than DSM20767^T. These overexpressed genes resulted in higher cytotoxicity and an increased immune response (i.e., TNF‐α, IL‐1β, TLR1 and INF‐γ) in the ASK cell line. This response was significantly higher against bacteria grown under iron‐limited conditions, especially H‐2. These observations indicate that iron‐acquisition mechanisms are possibly highly related to the virulence and pathogenic capacity of R. salmoninarum. In conclusion, treatments that block iron‐uptake mechanisms or siderophore synthesis are attractive therapeutic approaches for treating R. salmoninarum, which causes significant aquaculture losses.