The coffee berry borer (Hypothenemus hampei) is the most devastating insect pest of coffee worldwide with its infestations decreasing crop yield by up to 80%. Caffeine is an alkaloid that can be toxic to insects and is hypothesized to act as a defence mechanism to inhibit herbivory. Here we show that caffeine is degraded in the gut of H. hampei, and that experimental inactivation of the gut microbiota eliminates this activity. We demonstrate that gut microbiota in H. hampei specimens from seven major coffee-producing countries and laboratory-reared colonies share a core of microorganisms. Globally ubiquitous members of the gut microbiota, including prominent Pseudomonas species, subsist on caffeine as a sole source of carbon and nitrogen. Pseudomonas caffeine demethylase genes are expressed in vivo in the gut of H. hampei, and re-inoculation of antibiotic-treated insects with an isolated Pseudomonas strain reinstates caffeine-degradation ability confirming their key role.

Global climate models project a decrease in the magnitude of precipitation in tropical regions. Changes in rainfall patterns have important implications for the moisture content and redox status of tropical soils, yet little is known about how these changes may affect microbial community structure. Specifically, does exposure to prior stress confer increased resistance to subsequent perturbation? Here we reduced the quantity of precipitation throughfall to tropical forest soils in the Luquillo Mountains, Puerto Rico. Treatments included newly established throughfall exclusion plots (de novo excluded), plots undergoing reduction for a second time (pre-excluded) and ambient control plots. Ten months of throughfall exclusion led to a small but statistically significant decline in soil water potential and bacterial populations clearly adapted to increased osmotic stress. Although the water potential decline was small and microbial biomass did not change, phylogenetic diversity in the de novo-excluded plots decreased by B40% compared with the control plots, yet pre-excluded plots showed no significant change. On the other hand, the relative abundances of bacterial taxa in both the de novo-excluded and pre-excluded plots changed significantly with throughfall exclusion compared with control plots. Changes in bacterial community structure could be explained by changes in soil pore water chemistry and suggested changes in soil redox. Soluble iron declined in treatment plots and was correlated with decreased soluble phosphorus concentrations, which may have significant implications for microbial productivity in these P-limited systems.

Soil surface temperature, an important driver of terrestrial biogeochemical processes, depends strongly on soil albedo, which can be significantly modified by factors such as plant cover. In sparsely vegetated lands, the soil surface can be colonized by photosynthetic microbes that build biocrust communities. Here we use concurrent physical, biochemical and microbiological analyses to show that mature biocrusts can increase surface soil temperature by as much as 10 °C through the accumulation of large quantities of a secondary metabolite, the microbial sunscreen scytonemin, produced by a group of late-successional cyanobacteria. Scytonemin accumulation decreases soil albedo significantly. Such localized warming has apparent and immediate consequences for the soil microbiome, inducing the replacement of thermosensitive bacterial species with more thermotolerant forms. These results reveal that not only vegetation but also microorganisms are a factor in modifying terrestrial albedo, potentially impacting biosphere feedbacks on past and future climate, and call for a direct assessment of such effects at larger scales.

Global climate models predict a future of increased severity of drought in many tropical forests. Soil microbes are central to the balance of these systems as sources or sinks of atmospheric carbon (C), yet how they respond metabolically to drought is not well-understood. We simulated drought in the typically aseasonal Luquillo Experimental Forest, Puerto Rico, by intercepting precipitation falling through the forest canopy. This approach reduced soil moisture by 13% and water potential by 0.14 MPa (from -0.2 to -0.34). Previous results from this experiment have demonstrated that the diversity and composition of these soil microbial communities are sensitive to even small changes in soil water. Here, we show prolonged drought significantly alters the functional potential of the community and provokes a clear osmotic stress response, including the production of compatible solutes that increase intracellular C demand. Subsequently, a microbial population emerges with a greater capacity for extracellular enzyme production targeting macromolecular carbon. Significantly, some of these drought-induced functional shifts in the soil microbiota are attenuated by prior exposure to a short-term drought suggesting that acclimation may occur despite a lack of longer-term drought history.

Pelosinus spp. are fermentative firmicutes that were recently reported to be prominent members of microbial communities at contaminated subsurface sites in multiple locations. Here we report metabolic characteristics and their putative genetic basis in Pelosinus sp. strain HCF1, an isolate that predominated anaerobic, Cr(VI) T he throughput, depth, and reduced cost of second-generation DNA sequencing facilitate our ability to gain insight into a broad range of microbiological processes in the environment, and genome sequencing of prominent members of environmental microbial communities should contribute to the understanding of complex biogeochemical systems. Members of the Veillonellaceae, and particularly Pelosinus spp., have recently been reported to be among the more abundant bacterial taxa in chromate-reducing systems inoculated with material from the chromium-contaminated aquifer at the U.S. Department of Energy (DOE) Hanford 100H site in Washington State (1, 2) and in other contaminated aquifers (3-5). Chromate-reducing bacteria are of interest because in situ reductive immobilization is favored as one of the more cost-effective approaches to remediation of aquifers contaminated with Cr(VI), a potent toxicant, mutagen, and carcinogen (6, 7). Fermentative bacteria such as Pelosinus spp. may be of particular relevance to a common bioremediation scenario in which metabolism of organic electron donors (e.g., lactate-based polymers) injected into the subsurface readily consumes available electron acceptors (e.g., oxygen, nitrate, sulfate, and ferric iron) and drives the treated zone toward fermentative/methanogenic conditions.-In this article, we report on a variety of metabolic capabilities and their possible underlying genetic basis in a Pelosinus isolate that dominated a chromate-reducing community derived from aquifer sediment from the Hanford 100H site. The metabolic capabilities explored include lactate fermentation to propionate and acetate (related to the methylmalonyl-coenzyme A [CoA] pathway identified in the genome), Cr(VI) and Fe(III) reduction (both potentially related to identified flavoproteins), nitrate and nitrite reduction (potentially related to NrfH and NrfA as well as a membrane-bound, respiratory nitrate reductase), and H 2 metabolism (two [NiFe]-hydrogenases and four [FeFe]-hydrogenases were identified). We also report on focused transcriptional studies designed to more clearly associate certain genes with specific metabolic activities (namely, H 2 cycling and nitrate or nitrite reduction). Some metabolic activities and gene content reported here are unexpected for Pelosinus species and broaden our perspective on what metabolic and ecological roles this species might play in microbial communities in contaminated (and uncontaminated) environments. MATERIALS AND METHODSIsolation and cultivation of Pelosinus sp. strain HCF1. Pelosinus sp. strain HCF1 was isolated from the effluent of an anaerobic, chromatereducing, flowthrough column containing aquifer sediment from the DOE Hanford 100H site...