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Pseudomonas syringae is a bacterial complex that is widespread through a range of environments, typically associated with plants where it can be pathogenic, but also found in non-plant environments such as clouds, precipitation, and surface waters. Understanding its distribution within the environment, and the habitats it occupies, is important for examining its evolution and understanding behaviours. After a recent study found P. syringae living among a range of vascular plant species in Iceland, we questioned whether lichens could harbour P. syringae. Sixteen different species of lichens were sampled all over Iceland, but only one lichen genus, Peltigera, was found to consistently harbour P. syringae. Phylogenetic analyses of P. syringae from 10 sampling points where lichen, tracheophyte, and/or moss were simultaneously collected showed significant differences between sampling points, but not between different plants and lichens from the same point. Furthermore, while there were similarities in the P. syringae population in tracheophytes and Peltigera, the densities in Peltigera thalli were lower than in moss and tracheophyte samples. This discovery suggests P. syringae strains can localize and survive in organisms beyond higher plants, and thus reveals opportunities for studying their influence on P. syringae evolution., (© 2023 The Authors. Environmental Microbiology published by Applied Microbiology International and John Wiley & Sons Ltd.)

Bacterial communities form the basis of biogeochemical processes and determine plant growth and health. Mosses 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 in these environments. Here, we studied the total and potentially active bacterial communities associated with Racomitrium lanuginosum in response to a 20-yr 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, and nifH gene abundance. Warming changed both the total and the potentially active bacterial community structure, while litter abundance only affected the total bacterial community structure. The abundance of nifH genes was negatively affected by litter abundance. We also found shifts in the potentially nitrogen-fixing community, with Nostoc decreasing and noncyanobacterial diazotrophs increasing in relative abundance. Our data suggest that the moss microbial community and potentially nitrogen fixing taxa will be sensitive to future warming, partly via changes in litter and shrub abundance., (© 2021 The Authors. New Phytologist © 2021 New Phytologist Foundation.)

Within soil, bacteria are found in multispecies communities, where interactions can lead to emergent community properties. Studying bacteria in a social context is critical for investigating community-level functions. We previously showed that cocultured Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48 engage in interspecies social spreading (ISS) on a hard agar surface, a behavior which required close contact and depended on the nutritional environment. Here, we investigate whether 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 prevalent behavior found in one clade in the P. fluorescens group and two clades in the Pedobacter genus. We show that the interaction with certain Pedobacter isolates occurred without close contact, indicating induction of spreading by a putative diffusible signal. As with ISS by Pf0-1+V48, the motility of interacting pairs is influenced by the environment, with no spreading behaviors (or induction of motility) observed under high nutrient conditions. While Pf0-1+V48 require low nutrient but high NaCl conditions, in the broader range of interacting pairs, the high salt influence was variable. The prevalence of motility phenotypes observed here 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. IMPORTANCE Interspecies social spreading (ISS) is an emergent behavior observed when Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48 interact, during which both species move together across a surface. Importantly, this environment does not permit the movement of either individual species. This group behavior suggests that communities of microbes can function in ways not predictable by knowledge of the individual members. Here, we have asked whether ISS is widespread and thus potentially of importance in soil microbial communities. The significance of this research is the demonstration that surface spreading behaviors are not unique to the Pf0-1-V48 interaction but rather is a more widespread phenomenon observed among members of distinct clades of both P. fluorescens and Pedobacter isolates. Furthermore, we identify differences in mechanisms of signaling and nutritional requirements for ISS. Emergent traits resulting from bacterial interactions are widespread, and their characterization is necessary for a complete understanding of microbial community function.

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 amplicon sequence variants (ASVs) could only be detected in the potentially active community but not in the total community. Long-term warming led to increases in relative abundance of bacterial taxa 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., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Klarenberg, Keuschnig, Warshan, Jónsdóttir and Vilhelmsson.)

Natural gas seepage pockmarks are found off- and onshore in the Öxarfjörður graben, Iceland. The bacterial communities of two onshore seepage sites were analysed by 16S rRNA gene amplicon sequencing; the geochemical characteristics, hydrocarbon content, and the carbon isotope composition of the sites were also determined. While one site was found to be characterised by biogenic origin of methane gas, with a carbon isotope ratio (δ 13 C (‰)) of -63.2, high contents of organic matter and complex hydrocarbons, the other site showed a mixed origin of the methane gas (δ 13 C (‰) = -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 phylum Chloroflexi 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 , Bacteroidetes , Firmicutes , and Actinobacteria . This article describes the first microbial study on gas seepage pockmarks in Iceland.

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., (© FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Lichens are defined as the specific symbiotic structure comprising a fungus and a green alga and/or cyanobacterium. Up until recently, non-photobiont endothallic bacteria, while known to be present in large numbers, have generally been dismissed as functionally irrelevant cohabitants of the lichen thallus, or even environmental contaminants. Recent analyses of lichen metagenomes and innovative co-culture experiments have uncovered a functionally complex community that appears to contribute to a healthy lichen thallus in several ways. Lichen-associated bacteriomes are typically dominated by several lineages of Proteobacteria, some of which may be specific for lichen species. Recent work has implicated members of these lineages in several important ecophysiological roles. These include nutrient scavenging, including mobilization of iron and phosphate, nitrogen fixation, cellulase, xylanase and amylase activities, and oxidation of recalcitrant compounds, e.g. aromatics and aliphatics. Production of volatile organic compounds, conferring antibacterial and antifungal activity, has also been demonstrated for several lichen-associated isolates. In the present paper we review the nature of non-phototrophic endolichenic bacteria associated with lichens, and give insight into the current state of knowledge on their importance the lichen symbiotic association.

Although lichens are generally described as mutualistic symbioses of fungi and photosynthetic partners, they also harbour a diverse non-phototrophic microbiota, which is now regarded as a significant part of the symbiosis. However, the role of the non-phototrophic microbiota within the lichen is still poorly known, although possible functions have been suggested, including phosphate solubilization and various lytic activities. In the present study we focus on the bacterial biota associated with the foliose lichen Peltigera membranacea. To address our hypotheses on possible roles of the non-phototrophic microbiota, we used a metagenomic approach. A DNA library of bacterial sequence contigs was constructed from the lichen thallus material and the bacterial microbiota DNA sequence was analysed in terms of phylogenetic diversity and functional gene composition. Analysis of about 30,000 such bacterial contigs from the P. membranacea metagenome revealed significant representation of several genes involved in phosphate solubilization and biopolymer degradation., (© 2015 The Authors.)

While generally described as a bipartite mutualistic association between fungi and algae or cyanobacteria, lichens also host diverse and heretofore little explored communities of nonphototrophic endolichenic bacteria. The composition and possible roles of these bacterial communities in the lichen symbiotic association constitute an emerging field of research. Saxicolous (rock-dwelling) seashore lichens present an unusual environment, characterized by rapid fluctuations in temperature, salinity, exposure to solar radiation, etc. The present study focuses on the bacterial biota associated with 4 species of crustose, halophilic, saxicolous seashore lichens found in northern Iceland. A denaturing gradient gel electrophoresis based characterization of the composition of the lichen-associated microbiotas indicated that they are markedly lichen-species-specific and clearly distinguishable from the environmental microbiota represented by control sampling. A collection of bacterial strains was investigated and partially identified by 16S rDNA sequencing. The strains were found to belong to 7 classes: Alphaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, Cytophagia, Sphingobacteria, and Gammaproteobacteria. Several isolates display only a modest level of similarity to their nearest relatives found in GenBank, suggesting that they comprise previously undescribed taxa. Selected strains were tested for inorganic phosphate solubilization and biodegradation of several biopolymers, such as barley β-glucan, xylan, chitosan, and lignin. The results support a nutrient-scavenging role of the associate microbiota in the seashore lichen symbiotic association.

The protein expression profiles of two different age groups of Atlantic cod larvae, at 6 days post hatch (dph) and 24 dph, were compared using 2-dimensional electrophoresis and MALDI-TOF mass spectrometry analysis. The life stage of the cod larvae under study covers the first feeding period, generally characterized by high mortality in cod hatcheries. Despite visible morphological and functional changes in larvae from 6 to 24 dph, the pattern of abundant proteins is largely conserved. Interestingly, more than half of the proteins identified in the present study corresponded to different isoforms of the same proteins. The keratins showed the most pronounced developmental stage specific expression pattern. Type II keratins were more dominant in younger larvae and type I keratins in the older larval group. Four isoforms of the fast skeletal muscle alpha-actin, 3 isoforms of beta-2 tubulin and 2 isoforms of alpha-actin were detected. The different isoforms may be either encoded by different genes or generated by post-translational modifications (PTMs) of the same gene product. The PTMs are largely overlooked by studies based on mRNA detection. Therefore, the proteome approach to understanding the cellular mechanisms underlying fish development is important.

The effects of different humectants (sodium chloride, sucrose, and glycerol) on the growth of and compatible solute (glycine betaine, proline, and carnitine) uptake by the osmotolerant foodborne pathogen Staphylococcus aureus were investigated. While growth in the presence of the impermeant humectants sodium chloride and sucrose induced the accumulation of proline and glycine betaine by cells, growth in the presence of the permeant humectant glycerol did not. When compatible solutes were omitted from low-water-activity media, growth was very poor in the presence of impermeant humectants. In contrast, the addition of compatible solutes had essentially no effect on growth when cells were grown in low-water-activity media containing glycerol as the humectant. Carnitine was found to accumulate to high intracellular levels in osmotically stressed cells when proline and glycine betaine were absent, making it a potentially important compatible solute for this organism.

The pyruvate dehydrogenase multienzyme complex (PDHC) was found to be upregulated by osmotic stress in the osmotolerant pathogen Staphylococcus aureus. Upregulation was detectable in the levels of both activity and protein and was judged to be about fourfold when sodium chloride was used to adjust the water activity (a(w)) of the growth medium to 0.94. The upregulation of the PDHC was also found to be humectant dependent and was greatest when impermeant, nonmetabolizable humectants were used to adjust a(w). Further experiments provided evidence that in addition to osmotic upregulation, the PDHC complex is also subject to catabolite repression, thus providing a possible explanation for the observation that high concentrations of carbohydrates are generally more inhibitory to the growth of this bacterial pathogen than are high concentrations of salts.

Staphylococcus aureus is the most osmotolerant foodborne pathogen, and outbreaks of staphylococcal food poisoning are often linked to foods of reduced water activity (a(w)) values. While it is generally known that the thermal tolerance of microorganisms increases as the a(w) of the heating menstruum is decreased, surprisingly little research has examined the influence of growth medium a(w) on microbial thermal tolerance. In the present study, we show that growth of S. aureus at an a(w) value of 0.94 leads to the development of dramatically enhanced thermal tolerance (i.e., less than 1 log reduction after heating for 20 min at 60 degrees C). We further show that the identity of the accumulated compatible solute within cells grown at low a(w) can also influence the overall level of thermal tolerance of S. aureus. Finally, we provide evidence that the synthesis of general stress and/or osmotic stress proteins is required for the development of enhanced thermal tolerance of S. aureus at low a(w).