Dmitri Mavrodi1, Ankita Bhattacharyya1, Olga Mavrodi1, Linda Thomashow2 and David Weller2
1School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi,  Hattiesburg, MS, 2USDA-ARS Wheat Health,  Genetics and Quality Research Unit, Pullman, WA

Introduction. Climate change is among the most critical global concerns farmers face in the 21st century. Rhizosphere microbial communities positively influence plant fitness and offer much potential for improving crop resilience to drought and diseases. However, our understanding of the mechanisms through which water-stressed plants recruit rhizobacteria and the subsequent feedback of the rhizobiome to plant growth and fitness remains limited. 

Hypothesis. We hypothesize that the dryland rhizobiome differs from microbial communities of plants from well-watered soils and that the microbial adaptation to dryland conditions is mediated by changes in rhizodeposition. We performed a field study involving wheat grown in adjacent irrigated and dryland plots in Lind, WA, an area of the Inland Pacific Northwest currently experiencing an unprecedented heat wave and drought.

Methods and Results. The plots were sampled annually, and the bulk soil, rhizosphere, and endosphere microbiomes were characterized by 16S amplicon sequencing. We also collected and analyzed root exudates from water-replete and water-stressed plants. We cultured Pseudomonas synxantha 2-79, a beneficial strain isolated from wheat grown in Lind, in the presence of these root exudates and analyzed transcriptome changes by RNA-seq. We identified pronounced changes in the composition of communities associated with roots of wheat grown under dryland and irrigated conditions. The exposure of 2-79 to root exudates altered the expression of multiple genes, including those involved in the uptake and catabolism of quaternary ammonium compounds (QACs). These findings matched elevated amounts of choline and glycine betaine detected in root secretions of water-stressed wheat. In microorganisms, the QACs function as compatible solutes, and adding root exudates to 2-79 cultures efficiently protected the bacteria from water stress. 

Conclusions. Our results provide insight into the effects of drought on the plant microbiome and suggest that exudates play a key role in the survival of root-associated microorganisms in water-deprived conditions.

Citation/Acknowledgements. This work was supported by grants from NSF (award IOS-1656872) and the USDA National Institute of Food and Agriculture (NIFA) (award 2023-67019-40168). 

Natalie M. Meléndez-Vázquez1, Candelaria Gomez-Manzano2, Teresa Nguyen2, Juan Fueyo2, and Filipa Godoy-Vitorino1
1Department of Microbiology and Medical Zoology, University of Puerto Rico, Medical Sciences Campus, San Juan, PR, 2Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX

Introduction/Background. In glioblastoma (GBM), the most common primary brain tumor, less than 6% of patients survive 5 years following diagnosis. Particularly, in a phase I clinical trial, the oncolytic adenovirus Delta-24-RGD induced complete tumor regression in 20% of patients with recurrent GBM. However, not all viroimmunotherapy-treated patients responded to the therapy. Previous studies have shown a potential for gut microbiome-dependent strategies to influence immunotherapy response. Currently, there are no studies linking the gut microbiome to viroimmunotherapy efficacy.

Hypothesis/Goal of Study. We hypothesize that the gut microbiome plays an important role modulating the virus-driven anti-tumor response.

Methods and Results. To test this hypothesis, GBM cells were intracranially injected into immunocompetent C57BL/6 mice. Animals were treated orally with Indoximod, an inhibitor of immune modulator IDO, or with PBS or Delta-24-RGDOX, an oncolytic adenovirus armed with an OX-40L expression cassette, by intratumoral injections. A Naïve group with no tumor nor treatment was added as control. Fecal pellets were used for 16S microbiota assessment and community analysis. We found significant differences on gut bacterial structure in viroimmunotherapy-treated animals with higher survival. We also found differences in bacterial diversity between the Naïve and PBS groups, suggesting that the presence of tumors modifies the gut microbiota. Particularly, Bifidobacterium and Akkermansia were enriched in viroimmunotherapy responders. To evaluate the importance CD4+ T cells have regarding gut microbiome composition, we used another mice cohort but with combinatory therapies of Indoximod and Delta-24-RGDOX. CD4+ T cell depletion resulted in less survival, alterations to gut bacterial structure, and lower abundance of Bifidobacterium in viroimmunotherapy-treated mice.

Discussion/Conclusions. These findings suggest bacterial communities such as anti-inflammatory taxa may regulate host gut homeostasis and play a crucial role in the clinical outcome efficacy of Delta-24-RGDOX. These results highlight the importance of novel combinatorial therapies such as viroimmunotherapy with microbiome modulation to contribute to the success rate of treatments against solid tumors.

Citation/Acknowledgements. This project was funded by the University of Puerto Rico/MD Anderson Cancer Center Partnership for Excellence in Cancer Research award number 2U54CA096297-16 and the National Institute of Health (NIH) R01CA256006. Support was also given by NIMHD-RCMI grant number U54 MD007600 and grant #R25GM061838 of the National Institute of General Medical Sciences, Research Initiative for Scientific Enhancement (RISE).

Britton Strickland1, Kelly Moffat1, Huai Li1, Manoj Dadlani1, and Rita Colwell1,2
1CosmosID, Germantown, MD, 2Institute for Advanced Computer Studies, University of Maryland, College Park, MD

Abstract Embargoed