Biology subjects

Vilhelmsson, O.

Publications and source records attributed to Vilhelmsson, O..

8 recordsLinked to original sources

bioRxiv2024

Exploring the Exclusive Isolation of Pseudomonas syringae in Peltigera Lichens via metabolite analysis and growth assays

The specific association of the potentially plant-pathogenic Pseudomonas syringae with Peltigera lichens raises questions about the factors driving this host specificity. To explore this, the metabolic profile of seven lichen species belonging to three genera (Cladonia, Peltigera, and Stereocaulon) was analysed using LC-MSMS. Additionally, we assessed the growth of P. syringae strains in media supplemented with extracts from each lichen species. This revealed that Peltigera exhibits lower metabolite richness compared to other genera, but shows a higher chemical investment in specific compounds. Growth kinetics showed comparable P. syringae growth across lichen-supplemented media, except for C. arbuscula and Cladonia sp., where the former exhibited lower growth rates. Inhibition assays with lichen extracts showed no inhibition of P. syringae. The lichen metabolome is predominantly composed of lipids and organic acids. Furthermore, specific compounds, such as aminoglycosides, may facilitate P. syringae presence in Peltigera by inhibiting Bacillus subtilis and other antagonists. Additionally, compounds absent in Peltigera, like anthracene, might serve as a carbon source inhibitors like B. velezensis.

microbiology↗

bioRxiv2023

From lichens to crops: Pathogenic potential of Pseudomonas syringae from Peltigera lichens is similar to world-wide epidemic strains

The presence of bacteria belonging to the Pseudomonas syringae complex (P. syringae) in the natural vegetation of several Icelandic habitat types has been recently reported, raising questions about the risk to Icelandic crops, particularly given the expected increase in agricultural activity due to climate warming. This study takes advantage of Icelands unique characteristics and the discovery of P. syringae in Peltigera lichens to gain a better understanding of the potential risk posed by this newly discovered ecological niche. The main objective is to evaluate the pathogenic potential and fitness in crops of P. syringae strains isolated from Peltigera lichen sampled in Iceland, focusing on strains that belong to phylogroups 1 and 2, which commonly contain epidemic strains. The results indicate that P. syringae isolated from Icelandic Peltigera lichen have a comparable fitness to epidemic strains in eight out of ten tested plant species. Furthermore, pathogenicity assessment on three plant species highlighted that certain strains also caused similar symptoms and disease severity compared to epidemic strains. These findings provide valuable insights into the potential risks posed by P. syringae from Icelandic natural habitats and illustrate how strains from these habitats have a wide pathogenic potential to crops without having encountered these crops in the last several thousand years of their presence in Iceland.

microbiology↗

bioRxiv2022

Moss functional traits are important drivers for moss and underlying soil bacterial communities: evidence from a chronosequence in an Icelandic glacier forefield

Mosses are among the first colonizing organisms after glacier retreat and can develop into thick moss mats during later successional stages. They are key players in N2 fixation through their microbiome, which is an important process for nutrient build-up during primary succession. How these moss-microbe interactions develop during succession is not well-studied and is relevant in the light of climate change and increased glacier retreat. We examined how the bacterial communities associated with two moss species of the genus Racomitrium and the underlying substrate, as well as moss traits and nitrogen fixation, develop along a successional gradient in the glacier forefield of Flaajokull in southeast Iceland. In addition, tested whether moss functional traits, such as total carbon (TC) and nitrogen contents (TN) are drivers of moss and underlying soil bacterial communities. Although time since deglaciation did not affect TN and moisture content, TC and shoot length increased with time since deglaciation. Moss and underlying soil bacterial communities were distinct. While the soil bacterial community structure was driven by the time since deglaciation and moss C/N ratios, the moss bacterial community structure was linked to time since deglaciation and moss moisture content. Moss N2-fixation rates were linked to bacterial community composition and nifH gene abundance rather than moss TN or time since deglaciation. This was accompanied by a shift from autotrophic to heterotrophic diazotrophs. Overall, our results suggest that there is little lateral transfer between moss and soil bacterial communities and that moss traits and time since deglaciation affect moss and soil bacterial community structure. In addition, moss N2-fixation rates are determined by bacterial community structure, rather than moss traits or time since deglaciation.

ecology↗

bioRxiv2020

The total and active bacterial community of the chlorolichen Cetraria islandica and its response to long-term warming in sub-Arctic tundra

Lichens are traditionally defined as a symbiosis between a fungus and a green alga and or a cyanobacterium. This idea has been challenged by the discovery of bacterial communities inhabiting the lichen thalli. These bacteria are thought to contribute to the survival of lichens under extreme and changing environmental conditions. How these changing environmental conditions affect the lichen-associated bacterial community composition remains unclear. We describe the total (rDNA-based) and potentially metabolically active (rRNA-based) bacterial community of the lichen Cetaria islandica and its response to long-term warming using a 20-year warming experiment in an Icelandic sub-Arctic tundra. 16S rRNA and rDNA amplicon sequencing showed that the orders Acetobacterales (of the class Alphaproteobacteria) and Acidobacteriales (of the phylum Acidobacteria) dominated the bacterial community. Numerous ASVs (amplicon sequence variants) taxa could only be detected in the potentially active community but not in the total community. Long-term warming led to increases in relative abundance on class, order and ASV level. Warming altered the relative abundance of ASVs of the most common bacterial genera, such as Granulicella and Endobacter. The potentially metabolically active bacterial community was also more responsive to warming than the total community. Our results suggest that the bacterial community of the lichen C. islandica is dominated by acidophilic taxa and harbors disproportionally active rare taxa. We also show for the first time that climate warming can lead to shifts in lichen-associated bacterial community composition.

microbiology↗

bioRxiv2019

Long-term warming effects on the microbiome and nitrogen fixation associated with the moss Racomitrium lanuginosum in a subarctic alpine heathland

O_LIBacterial communities form the basis of biogeochemical processes and determine plant growth and health. Mosses, an abundant plant group in Arctic ecosystems, harbour diverse bacterial communities that are involved in nitrogen fixation and carbon cycling. Global climate change is causing changes in aboveground plant biomass and shifting species composition in the Arctic, but little is known about the response of moss microbiomes. C_LIO_LIHere, we studied the total and potentially active bacterial community associated with Racomitrium lanuginosum, in response to 20-year in situ warming in an Icelandic heathland. We evaluated the effect of warming and warming-induced shrub expansion on the moss bacterial community composition and diversity, nifH gene abundance and nitrogen-fixation rates. C_LIO_LIWarming changed both the total and the potentially active bacterial community structure, while litter abundance only affected the total bacterial community structure. The relative abundance of Proteobacteria increased, while the relative abundance of Cyanobacteria and Acidobacteria decreased. NifH gene abundance and nitrogen-fixation rates were negatively affected by litter and Betula nana abundance, respectively. We also found shifts in the potentially nitrogen-fixing community, with Nostoc decreasing and non-cyanobacterial diazotrophs increasing in relative abundance. Our data suggests that the moss microbial community including the potentially nitrogen-fixing taxa is sensitive to future warming. C_LIO_LISynthesis. Long-term warming led to a shift in moss-associated bacterial community composition, while the abundance of nitrogen-fixing bacteria and nitrogen-fixation rates were negatively affected by increased litter and Betula nana abundance respectively. Warming and increased shrub abundance as a result of warming can affect moss-associated bacterial communities and nitrogen fixation rates in tundra ecosystems. C_LI

microbiology↗

bioRxiv2019

Exploration of social spreading reveals behavior is prevalent among Pedobacter and P. fluorescens isolates, and shows variations in induction of phenotype

Within soil, bacteria are naturally found in multi-species communities, where interactions can lead to emergent community properties. It is critical that we study bacteria in a social context to investigate community-level functions. We previously showed that when co-cultured, Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48 engage in interspecies social spreading on a hard agar surface, a behavior which required close contact and was dependent on the nutritional environment. In this study, we investigate whether the ability to participate in social spreading is widespread among P. fluorescens and Pedobacter isolates, and whether the requirements for interaction vary. We find that this phenotype is not restricted to the interaction between P. fluorescens Pf0-1 and Pedobacter sp. V48, but is a more prevalent behavior found in one clade in the P. fluorescens group and two clades in the Pedobacter genus. We also discovered that the interaction with certain Pedobacter isolates occurred without close contact, indicating induction of spreading by a putative diffusible signal. As is the case for ISS by Pf0-1+V48, motility of all interacting pairs is influenced by the environment, with no spreading behaviors observed under high nutrient conditions. While Pf0-1+V48 require low nutrient but high NaCl conditions, in the broader range of interacting pairs this requirement for low nutrient and high salt was variable. The prevalence of motility phenotypes observed in this study and found within the literature indicates that community-induced locomotion in general, and social spreading in particular, is likely important within the environment. It is crucial that we continue to study microbial interactions and their emergent properties to gain a fuller understanding of the functions of microbial communities.

microbiology↗

bioRxiv2018

Xylanolytic psychrotrophs from andosolic sedge fens and moss heaths in Iceland

Nine xylanolytic bacterial strains were isolated from fen and heath soils in northern Iceland. They were found by 16S rRNA gene sequencing to belong to the genera Paenibacillus, Bacillus, Pseudomonas, and Stenotrophomonas. Using a simple, plate-based semiquantitative assay with azo-crosslinked xylan as the substrate, it was determined that although isolated from cold environments, most of the strains displayed greater xylanolytic activity under mesophilic conditions, with only the paenibacilli displaying markedly cold-active xylanolytic activity. Indeed, for one isolate, Paenibacillus castaneae OV2122, xylanolytic activity was only detected at 15{degrees}C and below under the conditions tested. Of the nine strains, Paenibacillus amylolyticus OV2121 displayed the greatest activity at 5{degrees}C. Glycohydrolase family-specific PCR indicated that the paenibacilli produced multiple xylanases of families 10 and 11, whereas a family 8 xylanase was detected in Pseudomonas kilonensis AL1515, and a family 11 xylanase in Stenotrophomonas rhizophila AL1610.

microbiology↗

bioRxiv2018

Gas seepage pockmark microbiomes suggest the presence of sedimentary coal seams in the Oxarfjordur graben of NE-Iceland

Natural gas seepage pockmarks are found off and onshore in the Oxarfjorthur graben, NE Iceland. The bacterial communities of two onshore seepage sites were analysed by amplicon sequencing of 16S rDNA, along with determining the geochemical characteristics, hydrocarbon content and the carbon isotope composition of the sites.\n\nWhile one site was found to be characterised by biogenic origin of methane gas, with carbon isotope ratio {delta}13C [{per thousand}] = -63.2, high content of organic matter and complex hydrocarbons, the other site showed a mixed origin of the methane gas ({delta}13C [{per thousand}] = -26.6) with geothermal characteristics and lower organic matter content. While both sites harboured Proteobacteria as the most abundant bacterial phyla, the Deltaproteobacteria were more abundant at the geothermal site, and the Alphaproteobacteria at the biogenic site. The Dehalococcoidia class of the Chloroflexi phylum was abundant at the geothermal site while the Anaerolineae class was more abundant at the biogenic site. Bacterial strains from the seepage pockmarks were isolated on a variety of selective media targeting bacteria with bioremediation potential. A total of 106 strains were isolated and characterised, including representatives from the phyla Proteobacteria, Bacterioidetes, Firmicutes, and Actinobacteria. This article describes the first microbial study on gas seepage pockmarks in Iceland.

microbiology↗