Project description:Microarrays are useful tools for detecting and quantifying specific functional and phylogenetic genes in natural microbial communities. In order to track uncultivated microbial genotypes and their close relatives in an environmental context, we designed and implemented a “genome proxy” microarray that targets microbial genome fragments recovered directly from the environment. Fragments consisted of sequenced clones from large-insert genomic libraries from microbial communities in Monterey Bay, the Hawaii Ocean Time-series station ALOHA, and Antarctic coastal waters. In a prototype array, we designed probe sets to thirteen of the sequenced genome fragments and to genomic regions of the cultivated cyanobacterium Prochlorococcus MED4. Each probe set consisted of multiple 70-mers, each targeting an individual ORF, and distributed along each ~40-160kbp contiguous genomic region. The targeted organisms or clones, and close relatives, were hybridized to the array both as pure DNA mixtures and as additions of cells to a background of coastal seawater. This prototype array correctly identified the presence or absence of the target organisms and their relatives in laboratory mixes, with negligible cross-hybridization to organisms having ≤~75% genomic identity. In addition, the array correctly identified target cells added to a background of environmental DNA, with a limit of detection of ~0.1% of the community, corresponding to ~10^3 cells/ml in these samples. Signal correlated to cell concentration with an R2 of 1.0 across six orders of magnitude. In addition the array could track a related strain (at 86% genomic identity to that targeted) with a linearity of R2=0.9999 and a limit of detection of ~1% of the community. Closely related genotypes were distinguishable by differing hybridization patterns across each probe set. This array’s multiple-probe, “genome-proxy” approach and consequent ability to track both target genotypes and their close relatives is important for the array’s environmental application given the recent discoveries of considerable intra-population diversity within marine microbial communities. Keywords: target addition experiment, proof-of-concept for GPL6012

Project description:To gain improved temporal, spatial and phylogenetic resolution of marine microbial communities, in this study we expanded the original prototype genome proxy array (an oligonucleotide microarray targeting marine microbial genome fragments and genomes), evaluated it against metagenomic sequencing, and applied it to time series samples from the Monterey Bay long term ecological research site. The expanded array targeted 268 microbial genotypes (vs. 14 in the original prototype) across much of the known diversity of cultured and uncultured marine microbes. The target abundances measured by the genome proxy array were highly correlated to pyrosequence-based abundances (linear regression R2 = 0.85-0.91, p<0.0001). Fifty-seven samples from ~4-years in Monterey Bay were examined with the array, spanning the photic zone (0m), the base of the surface mixed layer (30m), and the subphotic zone (200m). A significant portion of the expanded genome proxy array’s targets showed signal (95 out of 268 targets present in ≥ 1 sample). The multi-year community survey showed the consistent presence of a core group of common and abundant targeted taxa at each depth in Monterey Bay, higher variability among shallow than deep samples, and episodic occurrences of more transient marine genotypes. The abundance of the most dominant genotypes peaked after strong episodic upwelling events. The genome-proxy array’s ability to track populations of closely-related genotypes indicated population shifts within several abundant target taxa, with specific populations in some cases clustering by depth or oceanographic season. Although 51 cultivated organisms were targeted (representing 19% of the array) the majority of targets detected and of total target signal (85% and ~92%, respectively) were from uncultivated lineages, often those derived from Monterey Bay. The array provided cost-effective (~$15 per array, for construction and use) insights into the natural history of uncultivated lineages in the wild. To gain improved temporal, spatial and phylogenetic resolution of marine microbial communities, in this study we expanded the original prototype genome proxy array (an oligonucleotide microarray targeting marine microbial genome fragments and genomes), evaluated it against metagenomic sequencing, and applied it to time series samples from the Monterey Bay long term ecological research site. The expanded array targeted 268 microbial genotypes (vs. 14 in the original prototype) across much of the known diversity of cultured and uncultured marine microbes. The target abundances measured by the genome proxy array were highly correlated to pyrosequence-based abundances (linear regression R2 = 0.85-0.91, p<0.0001). Fifty-seven samples from ~4-years in Monterey Bay were examined with the array, spanning the photic zone (0m), the base of the surface mixed layer (30m), and the subphotic zone (200m). A significant portion of the expanded genome proxy array’s targets showed signal (95 out of 268 targets present in ≥ 1 sample). The multi-year community survey showed the consistent presence of a core group of common and abundant targeted taxa at each depth in Monterey Bay, higher variability among shallow than deep samples, and episodic occurrences of more transient marine genotypes. The abundance of the most dominant genotypes peaked after strong episodic upwelling events. The genome-proxy array’s ability to track populations of closely-related genotypes indicated population shifts within several abundant target taxa, with specific populations in some cases clustering by depth or oceanographic season. Although 51 cultivated organisms were targeted (representing 19% of the array) the majority of targets detected and of total target signal (85% and ~92%, respectively) were from uncultivated lineages, often those derived from Monterey Bay. The array provided cost-effective (~$15 per array, for construction and use) insights into the natural history of uncultivated lineages in the wild.

Project description:To gain improved temporal, spatial and phylogenetic resolution of marine microbial communities, in this study we expanded the original prototype genome proxy array (an oligonucleotide microarray targeting marine microbial genome fragments and genomes), evaluated it against metagenomic sequencing, and applied it to time series samples from the Monterey Bay long term ecological research site. The expanded array targeted 268 microbial genotypes (vs. 14 in the original prototype) across much of the known diversity of cultured and uncultured marine microbes. The target abundances measured by the genome proxy array were highly correlated to pyrosequence-based abundances (linear regression R2 = 0.85-0.91, p<0.0001). Fifty-seven samples from ~4-years in Monterey Bay were examined with the array, spanning the photic zone (0m), the base of the surface mixed layer (30m), and the subphotic zone (200m). A significant portion of the expanded genome proxy array’s targets showed signal (95 out of 268 targets present in ≥ 1 sample). The multi-year community survey showed the consistent presence of a core group of common and abundant targeted taxa at each depth in Monterey Bay, higher variability among shallow than deep samples, and episodic occurrences of more transient marine genotypes. The abundance of the most dominant genotypes peaked after strong episodic upwelling events. The genome-proxy array’s ability to track populations of closely-related genotypes indicated population shifts within several abundant target taxa, with specific populations in some cases clustering by depth or oceanographic season. Although 51 cultivated organisms were targeted (representing 19% of the array) the majority of targets detected and of total target signal (85% and ~92%, respectively) were from uncultivated lineages, often those derived from Monterey Bay. The array provided cost-effective (~$15 per array, for construction and use) insights into the natural history of uncultivated lineages in the wild. To gain improved temporal, spatial and phylogenetic resolution of marine microbial communities, in this study we expanded the original prototype genome proxy array (an oligonucleotide microarray targeting marine microbial genome fragments and genomes), evaluated it against metagenomic sequencing, and applied it to time series samples from the Monterey Bay long term ecological research site. The expanded array targeted 268 microbial genotypes (vs. 14 in the original prototype) across much of the known diversity of cultured and uncultured marine microbes. The target abundances measured by the genome proxy array were highly correlated to pyrosequence-based abundances (linear regression R2 = 0.85-0.91, p<0.0001). Fifty-seven samples from ~4-years in Monterey Bay were examined with the array, spanning the photic zone (0m), the base of the surface mixed layer (30m), and the subphotic zone (200m). A significant portion of the expanded genome proxy array’s targets showed signal (95 out of 268 targets present in ≥ 1 sample). The multi-year community survey showed the consistent presence of a core group of common and abundant targeted taxa at each depth in Monterey Bay, higher variability among shallow than deep samples, and episodic occurrences of more transient marine genotypes. The abundance of the most dominant genotypes peaked after strong episodic upwelling events. The genome-proxy array’s ability to track populations of closely-related genotypes indicated population shifts within several abundant target taxa, with specific populations in some cases clustering by depth or oceanographic season. Although 51 cultivated organisms were targeted (representing 19% of the array) the majority of targets detected and of total target signal (85% and ~92%, respectively) were from uncultivated lineages, often those derived from Monterey Bay. The array provided cost-effective (~$15 per array, for construction and use) insights into the natural history of uncultivated lineages in the wild. The expanded genome proxy array was designed as in (Rich et al., 2008). Briefly, each genotype was targeted using suites of ~20 70-mer oligonucleotide probes designed using the program ArrayOligoSelector (Zhu et al., 2003). Probes had approximately the same %GC (40%) and were distributed across the target genome or genome fragment, with no more than one probe per gene and avoiding 16S and 23S rRNA genes. The array included positive and negative control probes designed using the same method, to Halobacterium salinarum NRC-1 and a random genome sequence, respectively. The expanded array had a broader scope than the prototype of Rich et al., 2008 (268 target genotypes, as opposed to the prototype’s 14) and included a co-spot oligo for spot alignment and gridding purposes (using the “alien” oligo sequence of (Urisman et al., 2005). The targets were selected from fully-sequenced marine microbial genomes, publicly-available marine-derived BAC and fosmid clone sequences, and fully-sequenced clones from the lab’s Monterey Bay and Hawaii environmental BAC- and fosmid-based genomic libraries. Targeted genotypes are detailed in Table S1, summarized in Table S2, and presented in a schematic phylogenetic overview in Fig. 1. Previously-unpublished sequences used for array design were submitted to Genbank under accession numbers GU474833-GU474949. This submission presents the analysis of 57 samples, each hybridized to >= 3 arrays. In addition to negative control probes, for each hyrbdization date and run a negative control array was hyrbdized for which the input DNA was TE, taken through the entire aplification, labeling, and hybridization process.

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