Methylotrophic Methylobacterium bacteria nodulate and fix nitrogen in symbiosis with legumes

Rhizobia described so far belong to three distinct phylogenetic branches within the alpha-2 subclass of Proteobacteria. Here we report the discovery of a fourth rhizobial branch involving bacteria of the Methylobacterium genus. Rhizobia isolated from Crotalaria legumes were assigned to a new species, "Methylobacterium nodulans," within the Methylobacterium genus on the basis of 16S ribosomal DNA analyses. We demonstrated that these rhizobia facultatively grow on methanol, which is a characteristic of Methylobacterium spp. but a unique feature among rhizobia. Genes encoding two key enzymes of methylotrophy and nodulation, the mxaF gene, encoding the alpha subunit of the methanol dehydrogenase, and the nodA gene, encoding an acyltransferase involved in Nod factor biosynthesis, were sequenced for the type strain, ORS2060. Plant tests and nodA amplification assays showed that "M. nodulans" is the only nodulating Methylobacterium sp. identified so far. Phylogenetic sequence analysis showed that "M. nodulans" NodA is closely related to Bradyrhizobium NodA, suggesting that this gene was acquired by horizontal gene transfer.     

A field trial of alternative targeted screening strategies for Chagas disease in Arequipa, Peru

Background

Chagas disease is endemic in the rural areas of southern Peru and a growing urban problem in the regional capital of Arequipa, population ∼860,000. It is unclear how to implement cost-effective screening programs across a large urban and periurban environment.

Methods

We compared four alternative screening strategies in 18 periurban communities, testing individuals in houses with 1) infected vectors; 2) high vector densities; 3) low vector densities; and 4) no vectors. Vector data were obtained from routine Ministry of Health insecticide application campaigns. We performed ring case detection (radius of 15 m) around seropositive individuals, and collected data on costs of implementation for each strategy.

Results

Infection was detected in 21 of 923 (2.28%) participants. Cases had lived more time on average in rural places than non-cases (7.20 years versus 3.31 years, respectively). Significant risk factors on univariate logistic regression for infection were age (OR 1.02; p = 0.041), time lived in a rural location (OR 1.04; p = 0.022), and time lived in an infested area (OR 1.04; p = 0.008). No multivariate model with these variables fit the data better than a simple model including only the time lived in an area with triatomine bugs. There was no significant difference in prevalence across the screening strategies; however a self-assessment of disease risk may have biased participation, inflating prevalence among residents of houses where no infestation was detected. Testing houses with infected-vectors was least expensive. Ring case detection yielded four secondary cases in only one community, possibly due to vector-borne transmission in this community, apparently absent in the others.

Conclusions

Targeted screening for urban Chagas disease is promising in areas with ongoing vector-borne transmission; however, these pockets of epidemic transmission remain difficult to detect a priori. The flexibility to adapt to the epidemiology that emerges during screening is key to an efficient case detection intervention. In heterogeneous urban environments, self-assessments of risk and simple residence history questionnaires may be useful to identify those at highest risk for Chagas disease to guide diagnostic efforts.