Seasonality in land-ocean connectivity and local processes control sediment bacterial community structure and function in a High Arctic tidal flat

Climate change is altering patterns of precipitation, cryosphere thaw, and land-ocean influxes, affecting understudied Arctic estuarine tidal flats. These transitional zones between terrestrial and marine systems are hotspots for biogeochemical cycling, often driven by microbial processes. We investigated surface sediment bacterial community composition and function from May to September along a river-intertidal-subtidal-fjord gradient. We paired metabarcoding of in situ communities with in vitro carbon-source utilization assays. Bacterial communities differed in space and time, alongside varying environmental conditions driven by local seasonal processes and riverine inputs, with salinity emerging as the dominant structuring factor. Terrestrial and riverine taxa were found throughout the system, likely transported with runoff. In vitro assays revealed sediment bacteria utilized a broader range of organic matter substrates when incubated in fresh and brackish water compared to marine water. These results highlight the importance of salinity for ecosystem processes in these dynamic tidal flats, with the highest potential for utilization of terrestrially derived organic matter likely limited to tidal flat areas (and times) where sediments are permeated by freshwater. Our results demonstrate that intertidal flats must be included in future studies on impacts of increased riverine discharge and transport of terrestrial organic matter on coastal carbon cycling in a warming Arctic.

Identification and profiling of the community structure and potential function of bacteria from the fruiting bodies of Sanghuangporus vaninii

Sanghuangporus sp., a medicinal and edible homologous macrofungus known as 'forest gold', which has good effects on antitumor, hypolipidemia and the treatment of gynecological diseases. However, the natural resources of fruiting body are on the verge of depletion due to its long growth cycle and over exploitation. The growth and metabolism of macrofungi are known to depend on the diverse bacterial community. Here, we characterized the diversity and potential function of bacteria inhabiting in the fruiting body of the most widely applied S. vaninii using a combination method of high-throughput sequencing with pure culturing for the first time, and tested the biological activities of bacterial isolates, of which Illumina NovaSeq provided a more comprehensive results on the bacterial community structure. Total 33 phyla, 82 classes, 195 orders, 355 families, 601 genera and 679 species were identified in the fruiting body, and our results revealed that the community was predominated by the common Proteobacteria, Gammaproteobacteria, Burkholderiales, Methylophilaceae (partly consistent with pure-culturing findings), and was dominated by the genera of distinctive Methylotenera and Methylomonas (yet-uncultured taxa). Simultaneously, the functional analysis showed that companion bacteria were involved in the pathways of carbohydrate transport and metabolism, metabolism of terpenoids and polyketides, cell wall/membrane/envelope biogenesis, etc. Hence, it was inferred that bacteria associated with fruiting body may have the potential to adjust the growth, development and active metabolite production of host S. vaninii combined with the tested results of indole-3-acetic acid and total antioxidant capacity. Altogether, this report first provided new findings which can be inspiring for further in-depth studies to exploit bioactive microbial resources for increased production of Sanghuangporus, as well as to explore the relationship between medicinal macrofungi and their associated endophytes.

A Periplasmic Lanthanide Mediator, Lanmodulin, in Methylobacterium aquaticum Strain 22A

Methylobacterium and Methylorubrum species oxidize methanol via pyrroloquinoline quinone-methanol dehydrogenases (MDHs). MDHs can be classified into two major groups, Ca²⁺-dependent MDH (MxaF) and lanthanide (Ln³⁺)-dependent MDH (XoxF), whose expression is regulated by the availability of Ln³⁺. A set of a siderophore, TonB-dependent receptor, and an ABC transporter that resembles the machinery for iron uptake is involved in the solubilization and transport of Ln³⁺. The transport of Ln³⁺ into the cytosol enhances XoxF expression. A unique protein named lanmodulin from Methylorubrum extorquens strain AM1 was identified as a specific Ln³⁺-binding protein, and its biological function was implicated to be an Ln³⁺ shuttle in the periplasm. In contrast, it remains unclear how Ln³⁺ levels in the cells are maintained, because Ln³⁺ is potentially deleterious to cellular systems due to its strong affinity to phosphate ions. In this study, we investigated the function of a lanmodulin homolog in Methylobacterium aquaticum strain 22A. The expression of a gene encoding lanmodulin (lanM) was induced in response to the presence of La³⁺. A recombinant LanM underwent conformational change upon La³⁺ binding. Phenotypic analyses on lanM deletion mutant and overexpressing strains showed that LanM is not necessary for the wild-type and XoxF-dependent mutant’s methylotrophic growth. We found that lanM expression was regulated by MxcQE (a two-component regulator for MxaF) and TonB_Ln (a TonB-dependent receptor for Ln³⁺). The expression level of mxcQE was altered to be negatively dependent on Ln³⁺ concentration in ∆lanM, whereas it was constant in the wild type. Furthermore, when exposed to La³⁺, ∆lanM showed an aggregating phenotype, cell membrane impairment, La deposition in the periplasm evidenced by electron microscopy, differential expression of proteins involved in membrane integrity and phosphate starvation, and possibly lower La content in the membrane vesicle (MV) fractions. Taken together, we concluded that lanmodulin is involved in the complex regulation mechanism of MDHs and homeostasis of cellular Ln levels by facilitating transport and MV-mediated excretion.

Methyloradius palustris gen. nov., sp. nov., a methanol-oxidizing bacterium isolated from snow

A novel methylotrophic bacterium, strain Zm11^T, was isolated from reddish brown snow collected in a moor in Japan. Cells of the isolate were Gram-stain-negative, motile, and rod-shaped (0.6-0.7 × 1.2-2.7 μm). Growth was observed at 5-32 °C with an optimum growth temperature of 25-28 °C. The pH range for growth was 5.4-7.8 with an optimum pH of 6.8. The strain utilized only methanol as carbon and energy sources for aerobic growth. The major cellular fatty acids (> 40% of total) were summed feature 3 (C_16:1ω7c and/or C_16:1ω6c) and C_16: 0. The predominant quinone was Q-8, and major polar lipids were phosphatidylethanolamine and phosphatidylglycerol. The complete genome of strain Zm11^T is composed of a circular chromosome (2,800,413 bp), with G + C content of 46.4 mol%. Phylogenetic analyses were conducted based on the 16S rRNA gene sequence and conserved proteins encoded in the genome. The results of analyses indicate that strain Zm11^T is a member of the family Methylophilaceae but does not belong to any existing genus. On the basis of its genomic and phenotypic properties, strain Zm11^T (= DSM111909^T = NBRC114766^T) is proposed as the type strain of a new species in a new genus, Methyloradius palustris gen. nov., sp. nov.

Revealing the community and metabolic potential of active methanotrophs by targeted metagenomics in the Zoige wetland of the Tibetan Plateau

The Zoige wetland of the Tibetan Plateau is one of the largest alpine wetlands in the world and a major emission source of methane. Methane oxidation by methanotrophs can counteract the global warming effect of methane released in the wetlands. Understanding methanotroph activity, diversity and metabolism at the molecular level can guide the isolation of the uncultured microorganisms and inform strategy-making decisions and policies to counteract global warming in this unique ecosystem. Here we applied DNA stable isotope probing using ¹³ C-labelled methane to label the genomes of active methanotrophs, examine the methane oxidation potential and recover metagenome-assembled genomes (MAGs) of active methanotrophs. We found that gammaproteobacteria of type I methanotrophs are responsible for methane oxidation in the wetland. We recovered two phylogenetically novel methanotroph MAGs distantly related to extant Methylobacter and Methylovulum. They belong to type I methanotrophs of gammaproteobacteria, contain both mxaF and xoxF types of methanol dehydrogenase coding genes, and participate in methane oxidation via H₄ MPT and RuMP pathways. Overall, the community structure of active methanotrophs and their methanotrophic pathways revealed by DNA-SIP metagenomics and retrieved methanotroph MAGs highlight the importance of methanotrophs in suppressing methane emission in the wetland under the scenario of global warming.

Usitatibacter rugosus gen. nov., sp. nov. and Usitatibacter palustris sp. nov., novel members of Usitatibacteraceae fam. nov. within the order Nitrosomonadales isolated from soil

Members of the metabolically diverse order Nitrosomonadales inhabit a wide range of environments. Two strains affiliated with this order were isolated from soils in Germany and characterized by a polyphasic approach. Cells of strains 0125_3^T and Swamp67^T are Gram-negative rods, non-motile, non-spore-forming, non-capsulated and divide by binary fission. They tested catalase-negative, but positive for cytochrome c-oxidase. Both strains form small white colonies on agar plates and grow aerobically and chemoorganotrophically on SSE/HD 1 : 10 medium, preferably utilizing organic acids and proteinaceous substrates. Strains 0125_3^T and Swamp67^T are mesophilic and grow optimally without NaCl addition at slightly alkaline conditions. Major fatty acids are C_16 : 1  ω7c, C_16 : 0 and C_14 : 0. The major polar lipids are diphosphatidylglycerol, phosphatidylethanolamine and phosphatidyglycerol. The predominant respiratory quinone is Q-8. The G+C content for 0125_3^T and Swamp67^T was 67 and 66.1 %, respectively. The 16S rRNA gene analysis indicated that the closest relatives (<91 % sequence similarity) of strain 0125_3^T were Nitrosospira multiformis ATCC 25196^T, Methyloversatilis universalis FAM5^T and Denitratisoma oestradiolicum AcBE2-1^T, while Nitrosospira multiformis ATCC 25196^T, Nitrosospira tenuis Nv1^T and Nitrosospira lacus APG3^T were closest to strain Swamp67^T. The two novel strains shared 97.4 % 16S rRNA gene sequence similarity with one another and show low average nucleotide identity of their genomes (83.8 %). Based on the phenotypic, chemotaxonomic, genomic and phylogenetic analysis, we propose the two novel species Usitatibacter rugosus sp. nov (type strain 0125_3^T=DSM 104443^T=LMG 29998^T=CECT 9241^T) and Usitatibacter palustris sp. nov. (type strain Swamp67^T=DSM 104440^T=LMG 29997^T=CECT 9242^T) of the novel genus Usitatibacter gen. nov., within the novel family Usitatibacteraceae fam. nov.

Transposon mutagenesis for methylotrophic bacteria using Methylorubrum extorquens AM1 as a model system

Transposon mutagenesis utilizes transposable genetic elements that integrate into a recipient genome to generate random insertion mutations which are easily identified. This forward genetic approach has proven powerful in elucidating complex processes, such as various pathways in methylotrophy. In the past decade, many methylotrophic bacteria have been shown to possess alcohol dehydrogenase enzymes that use lanthanides (Lns) as cofactors. Using Methylorubrum extorquens AM1 as a model organism, we discuss the experimental designs, protocols, and results of three transposon mutagenesis studies to identify genes involved in different aspects of Ln-dependent methanol oxidation. These studies include a selection for transposon insertions that prevent toxic intracellular formaldehyde accumulation, a fluorescence-imaging screen to identify regulatory processes for a primary Ln-dependent methanol dehydrogenase, and a phenotypic screen for genes necessary for function of a Ln-dependent ethanol dehydrogenase. We anticipate that the methods described in this chapter can be applied to understand other metabolic systems in diverse bacteria.

Discovery of lanthanide-dependent methylotrophy and screening methods for lanthanide-dependent methylotrophs

The lanthanide elements (Lns) affect the physiology and growth of certain microorganisms known as "Ln-responsive microorganisms." Among them, in 2011, it was first reported that strains of Methylobacterium exhibited high methanol dehydrogenase (MDH) activity when grown in the presence of Lns; the purified Ln-inducible MDH was identified as XoxF-type MDH, whose catalytic function had previously been unknown. XoxF was the first enzyme to be identified as Ln-dependent, and its function in methylotrophy is more fundamental and important than that of the corresponding Ca²⁺-dependent MDH MxaFI. XoxF is encoded in the genomes of methylotrophic as well as non-methylotrophic bacteria. Thus, Lns are among the most fascinating and important growth factors for bacteria that potentially utilize methanol. Bacteria that require Lns for methanol growth are called "Ln-dependent methylotrophs." Recent findings indicate that these microorganisms comprise an "Ln-dependent ecosystem" that we have not been able to reconstruct under laboratory conditions without Lns. In this chapter, we summarize methods for (1) screening of Ln-responsive microorganisms, (2) purification of native XoxFs from Ln-dependent methylotrophs, and (3) screening of Ln-dependent methylotrophs from natural environments, while providing a history of the discovery of the Ln-dependent methylotrophs.