Amino Acid Analog Induces Stress Response in Marine Synechococcus.

Characterizing the cell-level metabolic trade-offs that phytoplankton exhibit in response to changing environmental conditions is important for predicting the impact of these changes on marine food web dynamics and biogeochemical cycling. The time-selective proteome-labeling approach, bioorthogonal noncanonical amino acid tagging (BONCAT), has potential to provide insight into differential allocation of resources at the cellular level, especially when coupled with proteomics. However, the application of this technique in marine phytoplankton remains limited. We demonstrate that the marine cyanobacteria Synechococcus sp. and two groups of eukaryotic algae take up the modified amino acid l-homopropargylglycine (HPG), suggesting that BONCAT can be used to detect translationally active phytoplankton. However, the impact of HPG addition on growth dynamics varied between groups of phytoplankton. In addition, proteomic analysis of Synechococcus cells grown with HPG revealed a physiological shift in nitrogen metabolism, general protein stress, and energy production, indicating a potential limitation for the use of BONCAT in understanding the cell-level response of Synechococcus sp. to environmental change. Variability in HPG sensitivity between algal groups and the impact of HPG on Synechococcus physiology indicates that particular considerations should be taken when applying this technique to other marine taxa or mixed marine microbial communities. IMPORTANCE Phytoplankton form the base of the marine food web and substantially impact global energy and nutrient flow. Marine picocyanobacteria of the genus Synechococcus comprise a large portion of phytoplankton biomass in the ocean and therefore are important model organisms. The technical challenges of environmental proteomics in mixed microbial communities have limited our ability to detect the cell-level adaptations of phytoplankton communities to a changing environment. The proteome labeling technique, bioorthogonal noncanonical amino acid tagging (BONCAT), has potential to address some of these challenges by simplifying proteomic analyses. This study explores the ability of marine phytoplankton to take up the modified amino acid, l-homopropargylglycine (HPG), required for BONCAT, and investigates the proteomic response of Synechococcus to HPG. We not only demonstrate that cyanobacteria can take up HPG but also highlight the physiological impact of HPG on Synechococcus, which has implications for future applications of this technique in the marine environment.

Diet breadth and exploitation of exotic plants shift the core microbiome of Cephaloleia, a group of tropical herbivorous beetles.

The beetle genus Cephaloleia has evolved in association with tropical ginger plants and for many species their specific host plant associations are known. Here we show that the core microbiome of six closely related Costa Rican Cephaloleia species comprises only eight bacterial groups, including members of the Acinetobacter, Enterobacteriacea, Pseudomonas, Lactococcus, and Comamonas. The Acinetobacter and Enterobacteriacea together accounted for 35% of the total average 16S rRNA ribotypes recovered from all specimens. Further, microbiome diversity and community structure was significantly linked to beetle diet breadth, between those foraging on less than two plant types (specialists) versus over nine plant types (generalists). Moraxellaceae, Enterobacteriaceae, and Pseudomonadaceae were highly prevalent in specialist species, and also present in eggs, while Rickettsiaceae associated exclusively with generalist beetles. Bacteria isolated from Cephaloleia digestive systems had distinct capabilities and suggested a possible beneficial role in both digestion of plant-based compounds, including xylose, mannitol, and pectin, and possible detoxification, via lipases. Cephaloleia species are currently expanding their diets to include exotic invasive plants, yet it is unknown whether their microbial community plays a role in this transition. In this study, colonization of invasive plants was correlated with a dysbiosis of the microbiome, suggesting a possible relationship between gut bacteria and niche adaptation.