Publications

4474

Huanglongbing (HLB) is one of the most destructive diseases of citrus worldwide. The three known causal agents of HLB are species of α-proteobacteria: ‘Candidatus Liberibacter asiaticus’, ‘Ca. L. africanus’, and ‘Ca. L. americanus’. Previous studies have found distinct variations in temperature sensitivity and tolerance among these species. Here, we describe the use of controlled heat treatments to cure HLB caused by ‘Ca. L. asiaticus’, the most prevalent and heat-tolerant species. Using temperature-controlled growth chambers, we evaluated the time duration and temperature required to suppress or eliminate the ‘Ca. L. asiaticus’ bacterium in citrus, using various temperature treatments for time periods ranging from 2 days to 4 months. Results of quantitative polymerase chain reaction (qPCR) after treatment illustrate significant decreases in the ‘Ca. L. asiaticus’ bacterial titer, combined with healthy vigorous growth by all surviving trees. Repeated qPCR testing confirmed that previously infected, heat-treated plants showed no detectable levels of ‘Ca. L. asiaticus’, while untreated control plants remained highly infected. Continuous thermal exposure to 40 to 42°C for a minimum of 48 h was sufficient to significantly reduce titer or eliminate ‘Ca. L. asiaticus’ bacteria entirely in HLB-affected citrus seedlings. This method may be useful for the control of ‘Ca. Liberibacter’-infected plants in nursery and greenhouse settings.

ABSTRACT Neoehrlichiosis caused by “ Candidatus Neoehrlichia mikurensis” is an emerging zoonotic disease. In total, six patients have been described in Europe, with the first case detected in 2007. In addition, seven patients from China were described in a report published in October 2012. In 2009, we diagnosed the first human case of “ Ca . Neoehrlichia mikurensis” infection in the Zurich area (Switzerland). Here, we report two additional human cases from the same region, which were identified by broad-range 16S rRNA gene PCR. Both patients were immunocompromised and presented with similar clinical syndromes, including fever, malaise, and weight loss. A diagnostic multiplex real-time PCR was developed for specific detection of “ Ca . Neoehrlichia mikurensis” infections. The assay is based on the signature sequence of a 280-bp fragment of the “ Ca . Neoehrlichia mikurensis” 16S rRNA gene and incorporates a “ Ca . Neoehrlichia mikurensis” species, a “ Ca . Neoehrlichia” genus, and an Anaplasmataceae family probe for simultaneous screening. The analytical sensitivity was determined to be below five copies of the “ Ca . Neoehrlichia mikurensis” 16S rRNA gene. Our results show that the assay is suitable for the direct detection of “ Ca . Neoehrlichia mikurensis” DNA in clinical samples from, for example, blood and bone marrow. In addition, it allows for monitoring treatment response during antibiotic therapy. Using the same assay, DNA extracts from 1,916 ticks collected in four forests in close proximity to the patients' residences (<3 km) were screened. At all sampling sites, the minimal prevalence of “ Ca . Neoehrlichia mikurensis” was between 3.5 to 8% in pools of either nymphs, males, or females, showing a strong geographic association between the three patients and the assumed vector.

A novel bacterial strain designated HA-01T was isolated from a freshwater terrestrial hot spring located at Hot Springs National Park, Arkansas, USA. Cells were Gram-negative-staining, rod-shaped, aerobic, chemo-organotrophic, oxidase- and catalase-positive, non-spore-forming and motile by means of a single polar flagellum. Growth occurred at 37–60 °C, with an optimum between 45 and 50 °C, and at pH 6.5–8.5, with an optimum between pH 6.5 and 7.0. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the closest relatives of strain HA-01T were Solimonas aquatica NAA-16T (93.8 %), Solimonas flava CW-KD 4T (94.1 %), Solimonas soli DCY12T (93.1 %), Solimonas variicoloris MN28T (94.0 %), Nevskia ramosa Soe1T (91.2 %) and Hydrocarboniphaga effusa AP103T (91.1 %). Major fatty acids consisted of C16 : 0, iso-C16 : 0, C16 : 1ω5c and summed feature 8 (C18 : 1ω9c, C18 : 1ω7c and C18 : 1ω6c). Polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine, and the major isoprenoid quinone was Q-8. The DNA G+C content was 64.4 mol%. Based on phylogenetic, phenotypic and chemotaxonomic evidence, it is proposed that strain HA-01T represents a novel species in a new genus for which the name Fontimonas thermophila gen. nov., sp. nov. is proposed. The type strain of the type species is HA-01T ( = DSM 23609T = CCUG 59713T). A new family, Solimonadaceae fam. nov., is also proposed to replace Sinobacteriaceae Zhou et al. 2008.