Microbes with higher metabolic independence are enriched in human gut microbiomes under stress

Changes in bumblebee queen gut microbiotas during and after overwintering diapause

Bumblebees are key pollinators with gut microbiotas that support host health. After bumblebee queens undergo winter diapause, which occurs before spring colony establishment, their gut microbiotas are disturbed, but little is known about community dynamics during diapause itself. Queen gut microbiotas also help seed worker microbiotas, so it is important that they recover post-diapause to a typical community structure, a process that may be impeded by pesticide exposure. We examined how bumblebee queen gut microbiota community structure and metabolic potential shift during and after winter diapause, and whether post-diapause recovery is affected by pesticide exposure. To do so, we placed commercial Bombus impatiens queens into diapause, euthanizing them at 0, 2 and 4 months of diapause. Additionally, we allowed some queens to recover from diapause for 1 week before euthanasia, exposing half to the common herbicide glyphosate. Using whole-community, shotgun metagenomic sequencing, we found that core bee gut phylotypes dominated queen gut microbiotas before, during and after diapause, but that two phylotypes, Schmidhempelia and Snodgrassella, ceased to be detected during late diapause and recovery. Despite fluctuations in taxonomic community structure, metabolic potential remained constant through diapause and recovery. Also, glyphosate exposure did not affect post-diapause microbiota recovery. However, metagenomic assembly quality and our ability to detect microbial taxa and metabolic pathways declined alongside microbial abundance, which was substantially reduced during diapause. Our study offers new insights into how bumblebee queen gut microbiotas change taxonomically and functionally during a key life stage and provides guidance for future microbiota studies in diapausing bumblebees.

Nutrient amendments enrich microbial hydrocarbon degradation metagenomic potential in freshwater coastal wetland microcosm experiments

Biostimulating native microbes with fertilizers has proven to be a highly effective strategy to speed up biodegradation rates in microbial communities. This study investigates the genetic potential of microbes to degrade light synthetic crude oil in a freshwater coastal wetland. Experimental sediment microcosms were exposed to a variety of conditions (biological control, a light synthetic crude oil amendment, and light synthetic crude oil with nutrient amendment) and incubated for 30 days before volatile organic compounds (BTEX) were quantified and DNA was sequenced for metagenomic analysis. The resulting DNA sequences were binned into metagenome-assembled genomes (MAGs). Analyses of MAGs uncovered a 13-fold significant increase in the abundance of rate-limiting hydrocarbon degrading monooxygenases and dioxygenases, identified only in MAGs from the light synthetic crude oil with nutrient amendments. Further, complete degradation pathways for BTEX compounds were found only in MAGs resulting from the light synthetic crude with nutrient amendment. Moreover, volatile organic compounds (BTEX, cyclohexane, and naphthalene) analyses of microcosm sediments in the presence of nutrients documented that benzene was degraded below detection limits, toluene (98%) and ethylbenzene (67%) were predominantly reduced within 30 days. Results indicate that the genetic potential to degrade BTEX compounds in this freshwater wetland can be linked to the functional potential for bioremediation. BTEX compounds are typically more recalcitrant and tougher to degrade than alkanes. This study demonstrated that stimulating a microbial community with nutrients to enhance its ability to biodegrade hydrocarbons, even in a relatively nutrient-rich habitat like a freshwater wetland, is an effective remediation tactic.

IMPORTANCE

The impact of oil spills in a freshwater aquatic environment can pose dire social, economic, and ecological effects on the region. An oil spill in the Laurentian Great Lakes region has the potential to affect the drinking water of more than 30 million people. The light synthetic crude oil used in this experimental microcosm study is transported through an underground pipeline crossing the waterway between two Laurentian Great Lakes. This study collected metagenomic data (experiments in triplicate) and assessed the quantity of BTEX compounds, which connected microbial degradation function to gene potential. The resulting data documented the bioremediation capabilities of native microbes in a freshwater coastal wetland. This study also provided evidence for this region that bioremediation can be a viable remediation strategy instead of invasive physical methods.

Disease-specific loss of microbial cross-feeding interactions in the human gut

Many gut microorganisms critical to human health rely on nutrients produced by each other for survival; however, these cross-feeding interactions are still challenging to quantify and remain poorly characterized. Here, we introduce a Metabolite Exchange Score (MES) to quantify those interactions. Using metabolic models of prokaryotic metagenome-assembled genomes from over 1600 individuals, MES allows us to identify and rank metabolic interactions that are significantly affected by a loss of cross-feeding partners in 10 out of 11 diseases. When applied to a Crohn's disease case-control study, our approach identifies a lack of species with the ability to consume hydrogen sulfide as the main distinguishing microbiome feature of disease. We propose that our conceptual framework will help prioritize in-depth analyses, experiments and clinical targets, and that targeting the restoration of microbial cross-feeding interactions is a promising mechanism-informed strategy to reconstruct a healthy gut ecosystem.