Biology subjects

Chase, A. B.

Publications and source records attributed to Chase, A. B..

7 recordsLinked to original sources

bioRxiv2024

Pattern-based genome mining guides discovery of the antibiotic indanopyrrole A from a marine streptomycete.

Terrestrial actinomycetes in the genus Streptomyces have long been recognized as prolific producers of small molecule natural products, including many clinically important antibiotics and cytotoxic agents. Although Streptomyces can also be isolated from marine environments, their potential for natural product biosynthesis remains underexplored. The MAR4 clade of largely marine-derived Streptomyces has been a rich source of novel halogenated natural products of diverse structural classes. To further explore the biosynthetic potential of this group, we applied pattern-based genome mining leading to the discovery of the first halogenated pyrroloketoindane natural products, indanopyrrole A (1) and B (2), and the bioinformatic linkage of these compounds to an orphan biosynthetic gene cluster (BCG) in 20 MAR4 genomes. Indanopyrrole A displays potent broad-spectrum antibiotic activity against clinically relevant pathogens. A comparison of the putative indanopyrrole BGC with that of the related compound indanomycin provides new insights into the terminal cyclization and offloading mechanisms in pyrroloketoindane biosynthesis. Broader searches of public databases reveal the rarity of this BGC while also highlighting opportunities for discovering additional compounds in this uncommon class. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/620887v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@14d6080org.highwire.dtl.DTLVardef@fa89b5org.highwire.dtl.DTLVardef@66fdddorg.highwire.dtl.DTLVardef@1a4f7f9_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Substrate complexity buffers negative interactions in a synthetic microbial community of leaf litter degraders.

Microbes associated with leaf litter, the top layer of soil, collectively decompose organic matter such as plant polysaccharides, and respire carbon dioxide, regulating the land-atmosphere fluxes of carbon. Therefore, it is crucial to understand the processes limiting biopolymer degradation and their influences on soil community properties. For example, it is still unclear how substrate complexity - defined as the structure of the saccharide and the amount of external processing by extracellular enzymes - influences species interactions and species coexistence. Here, we tested the hypothesis that growth on monosaccharides (i.e., xylose) promotes negative interactions through resource competition, and growth on polysaccharides (i.e., xylan) promotes neutral or positive interactions through resource partitioning or synergism among extracellular enzymes. We assembled a three-species community of leaf litter-degrading bacteria isolated from a grassland site in Southern California. In the polysaccharide xylan, pairs of species stably coexisted and grew equally in co-culture and in monoculture. Conversely, in the monosaccharide xylose, competitive exclusion and negative interactions prevailed. These pairwise dynamics remained consistent in a three-species community: all three species coexisted in xylan, while only two species coexisted in xylose. A mathematical model parameterized from single-species growth behaviors showed that in xylose these dynamics could be explained by resource competition. Instead, the resource competition model could not predict the coexistence patterns in xylan. Overall, our study shows that substrate complexity influences species interactions and patterns of coexistence in a synthetic microbial community of leaf litter degraders that can serve as a model for studying carbon cycling and climate change. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/573222v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@abf5aeorg.highwire.dtl.DTLVardef@18e99d5org.highwire.dtl.DTLVardef@1158650org.highwire.dtl.DTLVardef@252623_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

Small Molecule in situ Resin Capture - an Organism Independent Strategy for Natural Product Discovery.

Microbial natural products remain an important resource for drug discovery. Yet, commonly employed discovery techniques are plagued by the rediscovery of known compounds, the relatively few microbes that can be cultured, and laboratory growth conditions that do not elicit biosynthetic gene expression among myriad other challenges. Here we introduce a culture independent approach to natural product discovery that we call the Small Molecule In situ Resin Capture (SMIRC) technique. SMIRC exploits in situ environmental conditions to elicit compound production and represents a new approach to access poorly explored chemical space by capturing natural products directly from the environments in which they are produced. In contrast to traditional methods, this compound-first approach can capture structurally complex small molecules across all domains of life in a single deployment while relying on Nature to provide the complex and poorly understood environmental cues needed to elicit biosynthetic gene expression. We illustrate the effectiveness of SMIRC in marine habitats with the discovery of numerous new compounds and demonstrate that sufficient compound yields can be obtained for NMR-based structure assignment. Two new compound classes are reported including one novel carbon skeleton that possesses a functional group not previously observed among natural products and a second that possesses potent biological activity. We introduce expanded deployments, in situ cultivation, and metagenomics as methods to facilitate compound discovery, enhance yields, and link compounds to producing organisms. This compound first approach can provide unprecedented access to new natural product chemotypes with broad implications for drug discovery. Significance StatementPharmaceutically relevant microbial natural products have traditionally been discovered using a microbe-first approach in which bioassays are used to guide the isolation of active compounds from crude culture extracts. While once productive, it is now widely recognized that this approach fails to access the vast chemical space predicted from microbial genomes. Here, we report a new approach to natural product discovery in which compounds are captured directly from the environments in which they are produced. We demonstrate the applications of this technique with the isolation and identification of both known and new compounds including several that possess new carbon skeletons and one with promising biological activity.

biochemistry↗

bioRxiv2023

Metagenomic Data Reveal Type I Polyketide Synthase Distributions Across Biomes

Microbial polyketide synthase (PKS) genes encode the biosynthesis of many biomedically important natural products, yet only a small fraction of natures polyketide biosynthetic potential has been realized. Much of this potential originates from type I PKSs (T1PKSs), which can be delineated into different classes and subclasses based on domain organization and structural features of the compounds encoded. Notably, phylogenetic relationships among PKS ketosynthase (KS) domains provide a method to classify the larger and more complex genes in which they occur. Increased access to large metagenomic datasets from diverse habitats provides opportunities to assess T1PKS biosynthetic diversity and distributions through the analysis of KS domain sequences. Here, we used the webtool NaPDoS2 to detect and classify over 35,000 type I KS domains from 137 metagenomic data sets reported from eight diverse biomes. We found biome-specific separation with soils enriched in modular cis-AT and hybrid cis-AT KSs relative to other biomes and marine sediments enriched in KSs associated with PUFA and enediyne biosynthesis. By extracting full-length KS domains, we linked the phylum Actinobacteria to soil-specific enediyne and cis-AT clades and identified enediyne and monomodular KSs in phyla from which the associated compound classes have not been reported. These sequences were phylogenetically distinct from those associated with experimentally characterized PKSs suggesting novel structures or enzyme functions remain to be discovered. Lastly, we employed our metagenome-extracted KS domains to evaluate commonly used type I KS PCR primers and identified modifications that could increase the KS sequence diversity recovered from amplicon libraries. ImportancePolyketides are a crucial source of medicines, agrichemicals, and other commercial products. Advances in our understanding of polyketide biosynthesis coupled with the accumulation of metagenomic sequence data provide new opportunities to assess polyketide biosynthetic potential across biomes. Here, we used the webtool NaPDoS2 to assess type I PKS diversity and distributions by detecting and classifying KS domains across 137 metagenomes. We show that biomes are differentially enriched in KS domain classes, providing a roadmap for future biodiscovery strategies. Further, KS phylogenies reveal both biome-specific clades that do not include biochemically characterized PKSs, highlighting the biosynthetic potential of poorly explored environments. The large metagenome-derived KS dataset allowed us to identify regions of commonly used type I KS PCR primers that could be modified to capture a larger extent of KS diversity. These results facilitate both the search for novel polyketides and our understanding of the biogeographical distribution of PKSs across earths major biomes.

microbiology↗

bioRxiv2021

High fiber, whole foods dietary intervention alters the human gut microbiome but not fecal short-chain fatty acids

Dietary shifts can have a direct impact on the gut microbiome by preferentially selecting for microbes capable of utilizing the various dietary nutrients. Intake of dietary fiber has decreased precipitously in the last century, while consumption of processed foods has increased. Fiber, or microbiota-accessible carbohydrates (MACs), persist in the digestive tract and can be metabolized by specific bacteria encoding fiber degrading enzymes. Digestion of MACs results in the accumulation of short-chain fatty acids (SCFAs) and other metabolic byproducts that are critical to human health. Here, we implemented a two-week dietary fiber intervention aiming for 40-50 grams of fiber per day within the context of a course-based undergraduate research experience (CURE) (n = 20). By coupling shotgun metagenomic sequencing and targeted gas-chromatography mass spectrometry (GC/MS), we found that the dietary intervention significantly altered the composition of individual gut microbiomes, accounting for 8.3% of the longitudinal variability within subjects. Notably, microbial taxa that increased in relative abundance as a result of the diet change included known MAC degraders (i.e., Bifidobacterium and Lactobacillus). We further assessed the genetic diversity within Bifidobacterium, assayed by amplification of the groEL gene. Concomitant with microbial composition changes, we show an increase in the abundance of genes involved in inositol degradation. Despite these changes in gut microbiome composition, we did not detect a consistent shift in SCFA abundance. Collectively, our results demonstrate that on a short-term timescale of two weeks, increased fiber intake can induce compositional changes of the gut microbiome, including an increase in MAC degrading bacteria. IMPORTANCEA profound decrease in the consumption of dietary fiber in many parts of the world in the last century may be associated with the increasing prevalence of Type II diabetes, colon cancer, and other health problems. A typical U.S. diet includes about [~]15 grams of fiber per day, far less fiber than daily recommended allowance. Changes in dietary fiber intake affect human health not only through the uptake of nutrients directly, but also indirectly through changes in the microbial community and their associated metabolism. Here we conducted a two-week diet intervention in healthy young adults to investigate the impact of fiber consumption on the gut microbiome. Participants increased their average fiber consumption by 25 grams/day on average for two weeks. The high fiber diet intervention altered the gut microbiome of the study participants, including increases in known fiber degrading microbes such as Bifidobacterium and Lactobacillus.

microbiology↗

bioRxiv2020

Complex evolutionary dynamics govern the diversity and distribution of biosynthetic gene clusters and their encoded specialized metabolites

While specialized metabolites are thought to mediate ecological interactions, the evolutionary processes driving their diversification, particularly among closely related lineages, remain poorly understood. Here, we examine the evolutionary dynamics governing the distribution of natural product biosynthetic gene clusters (BGCs) using 118 strains within the marine actinomycete genus Salinispora. While previous evidence indicated that horizontal gene transfer (HGT) largely contributed to BGC diversity, we find that a majority of BGCs in Salinispora genomes are conserved through processes of vertical descent. In particular, vertical inheritance maintained BGCs over evolutionary timescales (millions of years) allowing for BGC diversification among Salinispora species. By coupling the genomic analyses with high-resolution tandem mass spectrometry (LC-MS/MS), we identified that BGC evolution in Salinispora proceeds largely through gene gain/loss events and constrained recombination that contributes to interspecies diversity at the gene, pathway, and metabolite levels. Consequently, the evolutionary processes driving BGC diversification had direct consequences for compound production and contributed to chemical diversification, as exemplified in our case study of the medically relevant proteosome inhibitors, the salinosporamides. Together, our results support the concept that specialized metabolites, and their cognate BGCs, represent functional traits associated with niche differentiation among Salinispora species. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=107 SRC="FIGDIR/small/423547v2_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@aef190org.highwire.dtl.DTLVardef@17536baorg.highwire.dtl.DTLVardef@5bf336org.highwire.dtl.DTLVardef@bc7d2f_HPS_FORMAT_FIGEXP M_FIG C_FIG O_TEXTBOXSIGNIFICANCENatural products are traditionally exploited for their pharmaceutical potential; yet what is often overlooked is that the evolution of the biosynthetic gene clusters (BGCs) encoding these small molecules likely affects the diversification of the produced compounds and implicitly has an impact on the compounds activities and ecological functions. And while the prevailing dogma in natural product research attributes frequent and widespread horizontal gene transfer (HGT) as an integral driver of BGC evolution, we find that the majority of BGC diversity derives from processes of vertical descent, with HGT events being rare. This understanding can facilitate informed biosynthetic predictions to identify novel natural products, in addition to uncovering how these specialized metabolites contribute to the environmental distribution of microbes. C_TEXTBOX

microbiology↗

bioRxiv2019

Sympatric and allopatric differentiation delineate population structure in a free-living terrestrial bacterium

In free-living bacteria and archaea, the equivalent of the biological species concept does not exist, creating several barriers to the study of the processes contributing to microbial diversification. As such, microorganisms are often operationally defined using conserved marker genes (i.e., 16S rRNA gene) or whole-genome measurements (i.e., ANI) to interpret intra-specific processes. However, as in eukaryotes, investigations into microbial populations must consider the potential for interacting genotypes among individuals that are subjected to similar environmental selective pressures. Therefore, we isolated 26 strains within a single bacterial ecotype (equivalent to a eukaryotic species definition) from a common habitat (leaf litter) across a regional climate gradient and asked whether the genetic diversity in a free-living soil bacterium (Curtobacterium) was consistent with patterns of allopatric or sympatric differentiation. By examining patterns of gene flow, our results indicate that microbial populations are delineated by gene flow discontinuities and exhibit evidence for population-specific adaptation. We conclude that the genetic structure within this bacterium is due to both adaptation within localized microenvironments (isolation-by-environment) as well as dispersal limitation between geographic locations (isolation-by-distance).

evolutionary biology↗