Are lichens potential natural reservoirs for plant pathogens?

Wild mushrooms as potential reservoirs of plant pathogenic bacteria: a case study on Burkholderia gladioli

Fruit bodies (sporocarps) of wild mushrooms growing in natural environments play a substantial role in the preservation of microbial communities, for example, clinical and food-poisoning bacteria. However, the role of wild mushrooms as natural reservoirs of plant pathogenic bacteria remains almost entirely unknown. Furthermore, bacterial transmission from a mushroom species to agricultural plants has rarely been recorded in the literature. In September 2021, a creamy-white Gram-negative bacterial strain was isolated from the sporocarp of Suillus luteus (slippery jack) growing in Bermuda grass (Cynodon dactylon) lawn in Southern Iran. A similar strain was isolated from the same fungus in the same area in September 2022. Both strains were identified as Burkholderia gladioli based on phenotypic features as well as phylogeny of 16S rRNA and three housekeeping genes. The strains were not only pathogenic on white button mushrooms (Agaricus bisporus) but also induced hypersensitive reaction (HR) on tobacco and common bean leaves and caused soft rot on a set of diverse plant species, that is, chili pepper, common bean pod, cucumber, eggplant, garlic, gladiolus, narcissus, onion, potato, spring onion, okra, kohlrabi, mango, and watermelon. Isolation of plant pathogenic B. gladioli strains from sporocarp of S. luteus in two consecutive years in the same area could be indicative of the role of this fungus in the preservation of the bacterium in the natural environment. B. gladioli associated with naturally growing S. luteus could potentially invade neighboring agricultural crops, for example, vegetables and ornamentals. The potential role of wild mushrooms as natural reservoirs of phytopathogenic bacteria is further discussed.IMPORTANCEThe bacterial genus Burkholderia contains biologically heterogeneous strains that can be isolated from diverse habitats, that is, soil, water, diseased plant material, and clinical specimens. In this study, two Gram-negative pectinolytic bacterial strains were isolated from the sporocarps of Suillus luteus in September 2021 and 2022. Molecular phylogenetic analyses revealed that both strains belonged to the complex species Burkholderia gladioli, while the pathovar status of the strains remained undetermined. Biological investigations accomplished with pathogenicity and host range assays showed that B. gladioli strains isolated from S. luteus in two consecutive years were pathogenic on a set of diverse plant species ranging from ornamentals to both monocotyledonous and dicotyledonous vegetables. Thus, B. gladioli could be considered an infectious pathogen capable of being transmitted from wild mushrooms to annual crops. Our results raise a hypothesis that wild mushrooms could be considered as potential reservoirs for phytopathogenic B. gladioli.

Plant microbial diversity is suggested as the key to future biocontrol and health trends

The microbiome of plants plays a crucial role in both plant and ecosystem health. Rapid advances in multi-omics tools are dramatically increasing access to the plant microbiome and consequently to the identification of its links with diseases and to the control of those diseases. Recent insights reveal a close, often symbiotic relationship between microorganisms and plants. Microorganisms can stimulate germination and plant growth, prevent diseases, and promote stress resistance and general fitness. Plants and their associated microorganisms form a holobiont and have to be considered as co-evolved species assemblages consisting of bacterial, archaeal and diverse eukaryotic species. The beneficial interplay of the host and its microbiome is responsible for maintaining the health of the holobiont, while diseases are often correlated with microbial dysbioses. Microbial diversity was identified as a key factor in preventing diseases and can be implemented as a biomarker in plant protection strategies. Targeted and predictive biocontrol approaches are possible by developing microbiome-based solutions. Moreover, combined breeding and biocontrol strategies maintaining diversity and ecosystem health are required. The analysis of plant microbiome data has brought about a paradigm shift in our understanding of its role in health and disease and has substantial consequences for biocontrol and health issues.

Selective isolation of potentially phosphate-mobilizing, biosurfactant-producing and biodegradative bacteria associated with a sub-Arctic, terricolous lichen, Peltigera membranacea

Lichens are the symbiotic association of fungi and a photosynthetic partner. However, non-phototrophic bacteria are also present and thought to comprise an essential part of the lichen symbiosis, although their roles in the symbiosis are still poorly understood. In this study, we isolated and characterized 110 non-phototrophic bacterial lichen associates from thalli of the terricolous lichen Peltigera membranacea The biodegradative and other nutrient-scavenging properties studied among selected isolates were phosphate mobilization, biosurfactant production and degradation of napthalene and several biopolymers, suggesting organic and inorganic nutrient scavenging as roles for bacteria in the lichen symbiotic association. Identification by partial 16S rRNA gene sequencing revealed that the isolates comprised 18 genera within the Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes, many with high similarities with bacteria typically associated with the plant and rhizosphere environments, could suggest that plants may be important sources of terricolous lichen-associated bacteria, or vice versa.