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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.)

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.)

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.)

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).