Development and application of polymerase chain reaction primers based on fhcD for environmental detection of methanopterin-linked C1-metabolism in bacteria

Methylotrophs in natural habitats: current insights through metagenomics

The focus of this review is on the recent data from the omics approaches, measuring the presence of methylotrophs in natural environments. Both Bacteria and Archaea are considered. The data are discussed in the context of the current knowledge on the biochemistry of methylotrophy and the physiology of cultivated methylotrophs. One major issue discussed is the recent metagenomic data pointing toward the activity of "aerobic" methanotrophs, such as Methylobacter, in microoxic or hypoxic conditions. A related issue of the metabolic distinction between aerobic and "anaerobic" methylotrophy is addressed in the light of the genomic and metagenomic data for respective organisms. The role of communities, as opposed to single-organism activities in environmental cycling of single-carbon compounds, such as methane, is also discussed. In addition, the emerging issue of the role of non-traditional methylotrophs in global metabolism of single-carbon compounds and the role of methylotrophy pathways in non-methylotrophs is briefly mentioned.

Synergistic metabolism of a broad range of C1 compounds in the marine methylotrophic bacterium HTCC2181

The 1.3 Mbp genome of HTCC2181, a member of the abundant OM43 clade of coastal bacterioplankton, suggested it is an obligate methylotroph. Preliminary experiments demonstrated that methanol and formaldehyde, but not other common C1 compounds such as methylamine, could support growth. Methanol concentrations in seawater are reportedly < 100 nM, suggesting either that the flux of methanol through plankton pools is very rapid, or that methanol may not be the primary growth substrate for HTCC2181. Therefore, we investigated the apparent extreme substrate range restriction of HTCC2181 in greater detail. Growth rate and maximum cell density of HTCC2181 increased with methanol concentration, yielding a K(s) value of 19 µM. In contrast, no growth was observed in the presence of the methylated (C1) compounds, methyl chloride, trimethylamine-oxide (TMAO) or dimethylsulfoniopropionate (DMSP) when they were the sole substrates. However, growth rate, maximum cell density and cellular ATP content were significantly enhanced when any of these methylated compounds were provided in the presence of a limiting concentration of methanol. These observations fit a model in which the metabolic intermediate formaldehyde is required for net carbon assimilation, allowing C1 substrates that do not produce a formaldehyde intermediate to be oxidized for energy, but not assimilated into biomass. Rates of methanol and TMAO oxidation and assimilation were measured with (14)C-radiolabelled compounds in cultures of HTCC2181 and seawater microbial communities collected off the Oregon coast. The results indicated that in nature as well as in culture, C1 substrates are partitioned between those that are mainly oxidized to produce energy and those that are assimilated. These findings indicate that the combined fluxes of C1 compounds in coastal systems are sufficient to support significant populations of obligate methyltrophs by a metabolic strategy that involves the synergistic metabolism of multiple C1 compounds.

Temporal variability of coastal Planctomycetes clades at Kabeltonne station, North Sea

Members of the bacterial phylum Planctomycetes are reported in marine water samples worldwide, but quantitative information is scarce. Here we investigated the phylogenetic diversity, abundance, and distribution of Planctomycetes in surface waters off the German North Sea island Helgoland during different seasons by 16S rRNA gene analysis and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). Generally Planctomycetes are more abundant in samples collected in summer and autumn than in samples collected in winter and spring. Statistical analysis revealed that Planctomycetes abundance was correlated to the Centrales diatom bloom in spring 2007. The analysis of size-fractionated seawater samples and of macroaggregates showed that ~90% of the Planctomycetes reside in the >3-μm size fraction. Comparative sequence analysis of 184 almost full-length 16S rRNA genes revealed three dominant clades. The clades, named Planctomyces-related group A, uncultured Planctomycetes group B, and Pirellula-related group D, were monitored by CARD-FISH using newly developed oligonucleotide probes. All three clades showed recurrent abundance patterns during two annual sampling campaigns. Uncultured Planctomycetes group B was most abundant in autumn samples, while Planctomyces-related group A was present in high numbers only during late autumn and winter. The levels of Pirellula-related group D were more constant throughout the year, with elevated counts in summer. Our analyses suggest that the seasonal succession of the Planctomycetes is correlated with algal blooms. We hypothesize that the niche partitioning of the different clades might be caused by their algal substrates.

Methylotrophy in a lake: from metagenomics to single-organism physiology

This review provides a brief summary of ongoing studies in Lake Washington (Seattle, WA) directed at an understanding of the content and activities of microbial communities involved in methylotrophy. One of the findings from culture-independent approaches, including functional metagenomics, is the prominent presence of Methylotenera species in the site and their inferred activity in C(1) metabolism, highlighting the local environmental importance of this group. Comparative analyses of individual genomes of Methylophilaceae from Lake Washington provide insights into their genomic divergence and suggest significant metabolic flexibility.

Genomes of three methylotrophs from a single niche reveal the genetic and metabolic divergence of the methylophilaceae

The genomes of three representatives of the family Methylophilaceae, Methylotenera mobilis JLW8, Methylotenera versatilis 301, and Methylovorus glucosetrophus SIP3-4, all isolated from a single study site, Lake Washington in Seattle, WA, were completely sequenced. These were compared to each other and to the previously published genomes of Methylobacillus flagellatus KT and an unclassified Methylophilales strain, HTCC2181. Comparative analysis revealed that the core genome of Methylophilaceae may be as small as approximately 600 genes, while the pangenome may be as large as approximately 6,000 genes. Significant divergence between the genomes in terms of both gene content and gene and protein conservation was uncovered, including the varied presence of certain genes involved in methylotrophy. Overall, our data demonstrate that metabolic potentials can vary significantly between different species of Methylophilaceae, including organisms inhabiting the very same environment. These data suggest that genetic divergence among the members of this family may be responsible for their specialized and nonredundant functions in C₁ cycling, which in turn suggests means for their successful coexistence in their specific ecological niches.

The expanding world of methylotrophic metabolism

In the past few years, the field of methylotrophy has undergone a significant transformation in terms of discovery of novel types of methylotrophs, novel modes of methylotrophy, and novel metabolic pathways. This time has also been marked by the resolution of long-standing questions regarding methylotrophy and the challenge of long-standing dogmas. This chapter is not intended to provide a comprehensive review of metabolism of methylotrophic bacteria. Instead we focus on significant recent discoveries that are both refining and transforming the current understanding of methylotrophy as a metabolic phenomenon. We also review new directions in methylotroph ecology that improve our understanding of the role of methylotrophy in global biogeochemical processes, along with an outlook for the future challenges in the field.

Methylotrophy in freshwater Beggiatoa alba strains

Two freshwater strains of the gammaproteobacterium Beggiatoa alba, B18LD and OH75-2a, are able to use methanol as a sole carbon and energy source under microoxic conditions. Genes encoding a methanol dehydrogenase large-subunit homolog and four enzymes of the tetrahydromethanopterin-dependent C(1) oxidation pathway were identified in B18LD. No evidence of methanotrophy was detected.

Real-time detection of actively metabolizing microbes by redox sensing as applied to methylotroph populations in Lake Washington

Redox sensor green (RSG), a novel fluorescent dye from Invitrogen was employed as a tool for real-time detection of microbes metabolically active in situ, in combination with flow cytometry and cell sorting. Lake Washington sediment, an environment known for high rates of methane oxidation, was used as a model, and methylotrophs were targeted as a functional group. We first tested and optimized the performance of the dye with pure methylotroph cultures. Most cells in actively growing cultures were positive for staining, whereas in starved cultures, few cells fluoresced. However, starved cells could be activated by addition of substrate. High numbers of fluorescing cells were observed in a Lake Washington sediment sample, and activation of subpopulations of cells was demonstrated in response to methane, methanol, methylamine and formaldehyde. The fraction of the population activated by methane was investigated in more detail, by phylogenetic profiling. This approach showed that the major responding species were the Methylomonas species, previously isolated from the site, and Methylobacter species that have not yet been cultivated from Lake Washington. In addition, from the methane-stimulated fraction, uncultivated bacterial sequences were obtained that belonged to unclassified Deltaproteobacteria, unclassified Verrucomicrobiles and unclassified Acidobacteria, suggesting that these microbes may also be involved in methane metabolism. The approach was further tested for its utility in facilitating enrichment for functional types that possess specific metabolic activities but resist cultivation. It was demonstrated that in enrichment cultures inoculated with cells that were sorted after stimulation with methane, Methylobacter sequences could be detected, whereas in enrichment cultures inoculated by randomly sorted cells, Methylomonas species quickly outcompeted all other types.

Effect of wastewater treatment plant effluent on microbial function and community structure in the sediment of a freshwater stream with variable seasonal flow

We investigated the effects of wastewater treatment plant (WWTP) discharge on the ecology of bacterial communities in the sediment of a small, low-gradient stream in South Australia. The quantification of genes involved in the biogeochemical cycling of carbon and nitrogen was used to assess potential impacts on ecosystem functions. The effects of disturbance on bacterial community structure were assessed by PCR-denaturing gradient gel electrophoresis of 16S rRNA genes, and clone library analysis was used to phylogenetically characterize significant shifts. Significant (P < 0.05) shifts in bacterial community structures were associated with alteration of the sediment's physicochemical properties, particularly nutrient loading from the WWTP discharge. The effects were greatest at the sampling location 400 m downstream of the outfall where the stream flow is reduced. This highly affected stretch of sediment contained representatives of the gammaproteobacteria that were absent from less-disturbed sites, including Oceanospirillales and Methylococcaceae. 16S rRNA gene sequences from less-disturbed sites had representatives of the Caulobacteraceae, Sphingomonadaceae, and Nitrospirae which were not represented in samples from disturbed sediment. The diversity was lowest at the reference site; it increased with proximity to the WWTP outfall and declined toward highly disturbed (400 m downstream) sites (P < 0.05). The potential for biological transformations of N varied significantly with the stream sediment location (P < 0.05). The abundance of amoA, narG, and nifH genes increased with the distance downstream of the outfall. These processes are driven by N and C availability, as well as redox conditions. Together these data suggest cause and effect between nutrient loading into the creek, shift in bacterial communities through habitat change, and alteration of capacity for biogeochemical cycling of N.

Archaeal and bacterial community composition of sediment and plankton from a suboxic freshwater pond

We studied the composition of archaeal and bacterial communities present in the sediment and plankton of a shallow suboxic-to-anoxic freshwater pond with high organic matter input, as an example of a kind of inland freshwater system widely distributed in forests of temperate regions. Molecular surveys based on small subunit rRNA genes showed a remarkably high diversity of lineages within the Bacteria, with a total of 18 phyla or candidate divisions being detected, in addition to a few highly divergent phylotypes of unknown affiliation. We identified members of the five subdivisions of the Proteobacteria, as well as Acidobacteria, Verrucomicrobia, Planctomycetes, Bacteroidetes, Chlorobi, Actinobacteria, Firmicutes, Chloroflexi, Gemmatimonadetes, Spirochaetes, Fibrobacteres and the candidate divisions OD1, OP11, TM6, WS1, WS6 and Termite Group 1 ("Endobacteria"). Candidate division OD1 and beta-Proteobacteria were dominant in the environmental libraries of plankton and sediment, respectively. Archaea were also very diverse, but only members of the Euryarchaeota, including Methanosarcinales, Methanomicrobiales and some divergent lineages, were identified. The application of various species richness estimators confirmed the highly diverse nature of both plankton and sediment samples. The pond is a microbial-based complex ecosystem mainly fueled by the degradation of allochthonous organic matter that maintains tightly coupled carbon and sulfur cycles.

Diversity of Planctomycetes in soil in relation to soil history and environmental heterogeneity

Members of the Planctomycetes, which were once thought to occur primarily in aquatic environments, have been discovered in soils on five continents, revealing that these Bacteria are a widespread and numerically abundant component of microbial communities in soil. We examined the diversity of Planctomycetes in soil samples obtained from experimental plots at an agricultural site in order to assess the extent of Planctomycetes diversity in soil, to determine whether management effects such as past land cover and compost addition affected the composition of the Planctomycetes community, and to determine whether the observations made could provide insight into the ecological distribution of these organisms. Analysis of Planctomycetes 16S rRNA gene sequences revealed a total of 312 +/- 35 unique phylotypes in the soil at the site examined. The majority of these Planctomycetes sequences were unique, and the sequences had phylogenetic affiliations that included all major lineages in the Planctomycetaceae, as well as several novel groups of deeply divergent Planctomycetes. Both soil management history and compost amendment had significant effects on the Planctomycetes diversity, and variations in soil organic matter, Ca2+ content, and pH were associated with variations in the Planctomycetes community composition. In addition, Planctomycetes richness increased in proportion to the area sampled and was correlated with the spatial heterogeneity of nitrate, which was associated with the soil management history at the orchard site examined. This report provides the first systematic assessment of the diversity of Planctomycetes in soil and also provides evidence that the diversity of this group increases with area as defined by the general power law description of the taxon-area relationship.

Highly divergent genes for methanopterin-linked C1 transfer reactions in Lake Washington, assessed via metagenomic analysis and mRNA detection

The origins and the evolutionary history of tetrahydromethanopterin-linked C1 transfer reactions that are part of two environmentally important biotransformations, methylotrophy and methanogenesis, are still not well understood. In previous studies, we have expanded the known phylogenetic diversity of these reactions by identifying genes highly diverging from the ones associated with cultivated Proteobacteria, Planctomycetes, or Archaea (M. G. Kalyuzhnaya, M. E. Lidstrom, and L. Chistoserdova, Microb. Ecol. 48:463-472, 2004; M. G. Kalyuzhnaya, O. Nercessian, M. E. Lidstrom, and L. Chistoserdova, Environ. Microbiol. 7:1269-1274, 2005). Here we used a metagenomic approach to demonstrate that these divergent genes are present with high abundance in the microbial community inhabiting Lake Washington sediment. We also gained preliminary insights into the genomic composition of the organisms possessing these genes by sequencing genomic fragments from three uncultured microbes possessing the genes of interest. Phylogenetic analyses suggested that, although distantly related to each other, these organisms deeply diverge from known Bacteria and Archaea, with more relation to the former, suggesting their affiliation with a new bacterial phylum. We also demonstrate, via specific mRNA detection, that these divergent genes are expressed in the environment, pointing toward their potential role in local carbon cycling.

Analysis of fae and fhcD genes in Mono Lake, California

Genes for two enzymes of the tetrahydromethanopterin-linked C(1) transfer pathway (fae and fhcD) were detected in hypersaline, hyperalkaline Mono Lake (California), via PCR amplification and analysis. Low diversity for fae and fhcD was noted, in contrast to the diversity previously detected in a freshwater lake, Lake Washington (Washington).

Community-level analysis: genes encoding methanopterin-dependent enzymes

This chapter describes a set of novel tools for the environmental detection of C1 transfer functions linked to the cofactor methanopterin. These tools include degenerate environmental primers targeting four of the most conserved genes in the methanopterin-linked C1 transfer pathway in bacteria, fae, mtdB, mch, and fhcD, and extensive databases of the respective genes. The tools described are suitable for detecting methanopterin-linked formaldehyde-oxidizing capacity in natural microbial communities and for determining the phylogenetic affiliations of major phyla involved in single-carbon cycling in the environment. The range of detection includes a variety of methano- and methylotrophic groups, other proteobacterial species capable of methanopterin-mediated reactions, and a variety of planctomycetes, as well as groups of microbes with currently unknown phylogenetic affiliations.

MtdC, a novel class of methylene tetrahydromethanopterin dehydrogenases

Novel methylene tetrahydromethanopterin (H4MPT) dehydrogenase enzymes, named MtdC, were purified after expressing in Escherichia coli genes from, respectively, Gemmata sp. strain Wa1-1 and environmental DNA originating from unidentified microbial species. The MtdC enzymes were shown to possess high affinities for methylene-H4MPT and NADP but low affinities for methylene tetrahydrofolate or NAD. The substrate range and the kinetic properties revealed by MtdC enzymes distinguish them from the previously characterized bacterial methylene-H4MPT dehydrogenases, MtdA and MtdB. While revealing higher sequence similarity to MtdA enzymes, MtdC enzymes appear to fulfill a function homologous to the function of MtdB, as part of the H4MPT-linked pathway for formaldehyde oxidation/detoxification.

Bacterial populations active in metabolism of C1 compounds in the sediment of Lake Washington, a freshwater lake

Active members of the bacterial community in the sediment of Lake Washington, with special emphasis on C1 utilizers, were identified by employing two complementary culture-independent approaches: reverse transcription of environmental mRNA and 16S rRNA combined with PCR (RT-PCR) and stable-isotope probing (SIP) of DNA with the 13C-labeled C1 substrates methanol, methylamine, formaldehyde, and formate. Analysis of RT-PCR-amplified fragments of 16S rRNA-encoding genes revealed that gammaproteobacterial methanotrophs belonging to Methylobacter and Methylomonas dominate the active methylotroph population, while only one other known methylotrophic lineage, Methylophilaceae, was detected via this approach. Analysis of RT-PCR-amplified functional genes, pmoA and fae, allowed detection of alphaproteobacterial (Methylosinus) and gammaproteobacterial (Methylobacter, Methylomonas, and Methylomicrobium) methanotrophs, methylotrophs of the genus Methylobacterium, and yet-unidentified proteobacteria. SIP experiments allowed detection of a broad variety of groups actively metabolizing C1 compounds. Comparisons between 16S rRNA gene pools amplified from [13C]DNA and from [12C]DNA revealed that the proportion of Methylophilus-related sequences increased in the presence of [13C]methanol, [13C]methylamine, and [13C]formaldehyde; Novosphingobium-related sequences were enriched in the presence of [13C]methanol; Gemmatimonadaceae-related sequences were enriched in the presence of [13C]formaldehyde and [13C]formate; and Xanthomonadaceae-related sequences were enriched in the presence of [13C]formate. Analysis of fae genes amplified from [13C]DNAs isolated from different microcosms revealed specific shifts in populations in response to a specific C1 compound: Methylosinus sequences dominated the [13C]methanol microcosm pool, and beta- and gammaproteobacterial sequences dominated the [13C]methylamine microcosm pool. The [13C]formaldehyde microcosm was dominated by betaproteobacterial sequences and by sequences of a nonaffiliated group, while the [13C]formate microcosm was dominated by alpha- and betaproteobacterial sequences. Overall, these data point toward the presence of a diverse population of active methylotrophs in Lake Washington sediments and toward the existence of yet-uncultivated organisms.

Analysis of gene islands involved in methanopterin-linked C1 transfer reactions reveals new functions and provides evolutionary insights

In this study, the occurrence and chromosomal clustering of genes encoding C(1) transfer reactions linked to tetrahydromethanopterin (H(4)MPT) were analyzed in a variety of proteobacteria and in representatives of the Planctomycetes via genomic analysis or via partial sequencing by cosmid walking. Although a tendency for clustering was found common for the genes of interest, significant variations in gene order and the degree of clustering were uncovered both between and within different groups of Proteobacteria and between Proteobacteria and Planctomycetes. Phylogenetic analyses suggested that the evolution of genes encoding H(4)MPT-linked reactions in Proteobacteria involved lateral transfers within Proteobacteria and possibly between Proteobacteria and other phyla. Gene cluster comparisons revealed a number of novel genes potentially involved in the C(1) transfer reactions, and these were analyzed by mutation and expression analyses. Four genes, a homolog of pabB, and three genes conserved between methanogenic Archaea and Bacteria possessing H(4)MPT-linked functions, orfY, orf1, and afpA were shown to be involved in formaldehyde oxidation/detoxification, as judged by specific mutant phenotypes. In particular, pabB contributes to the biosynthesis of para-aminobenzoic acid, a precursor of both tetrahydrofolate and H(4)MPT, and afpA apparently encodes a novel dihydromethanopterin reductase, based on mutant complementation experiments.