Narnaviruses: novel players in fungal-bacterial symbioses.

Rhizopus microsporus is an early-diverging fungal species with importance in ecology, agriculture, food production, and public health. Pathogenic strains of R. microsporus harbor an intracellular bacterial symbiont, Mycetohabitans (formerly named Burkholderia). This vertically transmitted bacterial symbiont is responsible for the production of toxins crucial to the pathogenicity of Rhizopus and remarkably also for fungal reproduction. Here we show that R. microsporus can live not only in symbiosis with bacteria but also with two viral members of the genus Narnavirus. Our experiments revealed that both viruses replicated similarly in the growth conditions we tested. Viral copies were affected by the developmental stage of the fungus, the substrate, and the presence or absence of Mycetohabitans. Absolute quantification of narnaviruses in isolated asexual sporangiospores and sexual zygospores indicates their vertical transmission. By curing R. microsporus of its viral and bacterial symbionts and reinfecting bacteria to reestablish symbiosis, we demonstrate that these viruses affect fungal biology. Narnaviruses decrease asexual reproduction, but together with Mycetohabitans, are required for sexual reproductive success. This fungal-bacterial-viral system represents an outstanding model to investigate three-way microbial symbioses and their evolution.

Forest tree associated bacteria for potential biological control of Fusarium solani and of Fusarium kuroshium, causal agent of Fusarium dieback.

Although the use of crop-associated bacteria as biological control agents of fungal diseases has gained increasing interest, the biotechnological potential of forest tree-associated microbes and their natural products has scarcely been investigated. The objective of this study was to identify bacteria or bacterial products with antagonistic activity against Fusarium solani and Fusarium kuroshium, causal agent of Fusarium dieback, by screening the rhizosphere and phyllosphere of three Lauraceae species. From 195 bacterial isolates, we identified 32 isolates that significantly reduced the growth of F. solani in vitro, which mostly belonged to bacterial taxa Bacillus, Pseudomonas and Actinobacteria. The antifungal activity of their volatile organic compounds (VOCs) was also evaluated. Bacterial strain Bacillus sp. CCeRi1-002, recovered from the rhizosphere of Aiouea effusa, showed the highest percentage of direct inhibition (62.5 %) of F. solani and produced diffusible compounds that significantly reduced its mycelial growth. HPLC-MS analyses on this strain allowed to tentatively identify bioactive compounds from three lipopeptide groups (iturin, surfactin and fengycin). Bacillus sp. CCeRi1-002 and another strain identified as Pseudomonas sp. significantly inhibited F. solani mycelial growth through the emission of VOCs. Chemical analysis of their volatile profiles indicated the likely presence of 2-nonanone, 2-undecanone, disulfide dimethyl and 1-butanol 3-methyl-, which had been previously reported with antifungal activity. In antagonism assays against F. kuroshium, Bacillus sp. CCeRi1-002 and its diffusible compounds exhibited significant antifungal activity and induced hyphal deformations. Our findings highlight the importance of considering bacteria associated with forest species and the need to include bacterial products in the search for potential antagonists of Fusarium dieback.

Smells from the desert: Microbial volatiles that affect plant growth and development of native and non-native plant species.

The plant microbiota can affect host fitness via the emission of microbial volatile organic compounds (mVOCs) that influence growth and development. However, evidence of these molecules and their effects in plants from arid ecosystems is limited. We screened the mVOCs produced by 40 core and representative members of the microbiome of agaves and cacti in their interaction with Arabidopsis thaliana and Nicotiana benthamiana. We used SPME-GC-MS to characterize the chemical diversity of mVOCs and tested the effects of selected compounds on growth and development of model and host plants. Our study revealed that approximately 90% of the bacterial strains promoted plant growth both in A. thaliana and N. benthamiana. Bacterial VOCs were mainly composed of esters, alcohols, and S-containing compounds with 25% of them not previously characterized. Remarkably, ethyl isovalerate, isoamyl acetate, 3-methyl-1-butanol, benzyl alcohol, 2-phenylethyl alcohol, and 3-(methylthio)-1-propanol, and some of their mixtures, displayed beneficial effects in A. thaliana and also improved growth and development of Agave tequilana and Agave salmiana in just 60 days. Volatiles produced by bacteria isolated from agaves and cacti are promising molecules for the sustainable production of crops in arid and semi-arid regions.

Evaluation of microbial load in oropharyngeal mucosa from tannery workers.

BACKGROUND: Animal skin provides an ideal medium for the propagation of microorganisms and it is used like raw material in the tannery and footware industry. The aim of this study was to evaluate and identify the microbial load in oropharyngeal mucosa of tannery employees. METHODS: The health risk was estimated based on the identification of microorganisms found in the oropharyngeal mucosa samples. The study was conducted in a tanners group and a control group. Samples were taken from oropharyngeal mucosa and inoculated on plates with selective medium. In the samples, bacteria were identified by 16S ribosomal DNA analysis and the yeasts through a presumptive method. In addition, the sensitivity of these microorganisms to antibiotics/antifungals was evaluated. RESULTS: The identified bacteria belonged to the families Enterobacteriaceae, Pseudomonadaceae, Neisseriaceae, Alcaligenaceae, Moraxellaceae, and Xanthomonadaceae, of which some species are considered as pathogenic or opportunistic microorganisms; these bacteria were not present in the control group. Forty-two percent of bacteria identified in the tanners group are correlated with respiratory diseases. Yeasts were also identified, including the following species: Candida glabrata, Candida tropicalis, Candida albicans, and Candida krusei. Regarding the sensitivity test of bacteria identified in the tanners group, 90% showed sensitivity to piperacillin/tazobactam, 87% showed sensitivity to ticarcillin/clavulanic acid, 74% showed sensitivity to ampicillin/sulbactam, and 58% showed sensitivity to amoxicillin/clavulanic acid. CONCLUSION: Several of the bacteria and yeast identified in the oropharyngeal mucosa of tanners have been correlated with infections in humans and have already been reported as airborne microorganisms in this working environment, representing a health risk for workers.