Boulton, J. M. | Search bioRxiv

bioRxiv2024

Expansion and revision of the genus Xanthobacter and proposal of Roseixanthobacter gen. nov.

The nitrogen-fixing, chemolithoautotrophic genus Xanthobacter is found worldwide across numerous diverse environments and is an important member of many ecosystems. These species serve as model systems for their metabolic properties in academic settings and have industrial applications in bioremediation and sustainable protein, food, and fertilizer production. Despite their abundance, interest, and importance, the majority of Xanthobacter strains are without a genome sequence, and only 8 validly published species are known to date. To expand our understanding of the diversity and evolutionary history of the genus, we sequenced the genomes of 37 repository strains and 26 novel environmental strains we isolated. After performing comparative phylogenomic analyses, we expand and revise the genus Xanthobacter and propose the novel genus Roseixanthobacter gen. nov. For the Xanthobacter, we describe 10 novel species, bringing the total to 18: Xanthobacter agilis, Xanthobacter albus sp. nov., Xanthobacter aminoxidans, Xanthobacter autotrophicus, Xanthobacter cornucopiae sp. nov., Xanthobacter dioxanivorans, Xanthobacter flavus, Xanthobacter lutulentifluminis sp. nov., Xanthobacter nonsaccharivorans sp. nov., Xanthobacter oligotrophicus, Xanthobacter pseudotagetidis sp. nov., Xanthobacter sediminis sp. nov., Xanthobacter tagetidis, Xanthobacter toluenivorans sp. nov., Xanthobacter variabilis sp. nov., Xanthobacter versatilis sp. nov., Xanthobacter viscosus, and Xanthobacter wiegelii sp. nov. For the Roseixanthobacter gen. nov., we describe 5 novel species formerly classified as Xanthobacter: Roseixanthobacter finlandensis sp. nov., Roseixanthobacter glucoisosaccharinivorans sp. nov., Roseixanthobacter liquoris sp. nov., Roseixanthobacter pseudopolyaromaticivorans sp. nov., and Roseixanthobacter psychrophilus sp. nov. We characterized the phenotypic properties of these type strains, including temperature, salinity and pH ranges, carbon substrate utilization, motility, antibiotic susceptibility, slime production, autotrophic growth, and enzymatic activities. We discovered a more diverse range of phenotypes across the genus Xanthobacter than previously known and elucidated the evolutionary history within the genus. These findings and genome sequences will help further the application of Xanthobacter biology in academic, industrial, and environmental settings and provide additional insight into the unique biological properties that make these species attractive for such applications.

microbiology↗

bioRxiv2020

Exposure duration modulates the response of Caribbean corals to global change stressors

Global change is threatening coral reefs, with rising temperatures leading to repeat bleaching events (dysbiosis of coral hosts and their symbiotic algae) and ocean acidification reducing net coral calcification. Although global-scale mass bleaching events are revealing fine-scale patterns of coral resistance and resilience, traits that lead to persistence under environmental stress remain elusive. Here, we conducted a 95-day controlled-laboratory experiment to investigate how duration of exposure to ocean warming (28, 31{degrees}C), acidification (pCO2 = 400-2800 atm), and their interaction influence the physiological responses of two Caribbean reef-building coral species (Siderastrea siderea, Pseudodiploria strigosa) from two reef zones of the Belize Mesoamerican Barrier Reef System. Every 30 days, calcification rate, total host protein and carbohydrate, chlorophyll a pigment concentration, and symbiont cell density were quantified for the same coral colony to characterize acclimatory responses of each genotype. Physiologies of the two species were differentially affected by these stressors, with exposure duration modulating responses. Siderastrea siderea was most affected by extreme pCO2 (~2800 atm), which resulted in reduced calcification rate, symbiont density, and chlorophyll a concentration. Siderastrea siderea calcification rate initially declined under extreme pCO2 but recovered by the final time point, and overall demonstrated resistance to next-century pCO2 and temperature stress. In contrast, P. strigosa was more negatively impacted by elevated temperature (31{degrees}C). Reductions in P. strigosa calcification rate and total carbohydrates were consistently observed over time regardless of pCO2 treatment, with the greatest reductions observed under elevated temperature. However, nearshore colonies of P. strigosa maintained calcification rates under elevated temperature throughout all exposure durations, suggesting individuals from this environment may be locally adapted to the warmer temperatures characterizing their natal reef zone. This experiment highlights how tracking individual coral colony physiology across broad exposure durations can capture acclimatory responses of corals to global change stressors.

ecology↗