Biology subjects

Stewart, G. R.

Publications and source records attributed to Stewart, G. R..

4 recordsLinked to original sources

bioRxiv2026

RAPID DECLINE OF NESTING PEREGRINE FALCONS IN THE SAN FRANCISCO BAY REGION OF CALIFORNIA SYNCHRONOUS WITH AN H5N1 OUTBREAK

After rebounding from near extirpation during the organochlorine era, breeding Peregrine Falcons (Falco peregrinus) in California are again facing adversity, this time consistent with an outbreak of a highly pathogenic avian influenza. Following the first detection of the H5N1 variant clade 2.3.4.4b virus in California wild birds in July 2022, we assembled data from long-term monitoring (2000-2025) of peregrine breeding territory occupancy in the broad vicinity of San Francisco Bay to examine possible impacts on falcon populations. Prior to the outbreak, 47 focal breeding territories had shown nearly complete occupancy by pairs (98.5% of 390 site-years), with very few vacancies, single birds in attendance, or subadult pair members. Within 8 mo of the outbreak, occupancy had dropped to 65.1%, and 2 yrs later (2025), only 36.2% of sites remained occupied. An uptick in site-occupancy by single birds also occurred after the outbreak, but it is unclear whether these were survivors or floaters attempting to fill vacant territories where both pair members had perished. The high vacancy rates signaled an impact upon floaters (nonbreeding adults) that normally buffer breeding site-occupancy in healthy peregrine populations. From October 2022 through November 2025, 17 peregrine fatalities were diagnosed with H5N1 within the counties comprising our study area. Evidence that H5N1 caused these territory vacancies includes, (1) the striking temporal coincidence of occupancy loss with the outbreak, and (2) the lethality of the virus to peregrines and its confirmed presence in peregrine prey in our study area. Our study reaffirms the value of long-term territory occupancy monitoring in this sentinel species.

ecology↗

bioRxiv2023

Temporal genome-wide fitness analysis of Mycobacterium marinum during infection reveals genetic requirement for virulence and survival in amoebae and microglial cells

Tuberculosis remains the most pervasive infectious disease and the recent emergence of multiple or even fully drug-resistant strains increases the risk and emphasizes the need for more efficient and better drug treatments. A key feature of mycobacteria pathogenesis is the metabolic switch during infection and expression of virulence genes is often adapted to specific infection conditions. This study aims to identify genes that are involved in the establishment and maintenance of the infection. To answer these questions, we have applied Transposon Sequencing (Tn-Seq) in M. marinum, an unbiased genome-wide strategy that combines saturation insertional mutagenesis and high throughput sequencing. This approach allowed us to precisely identify the localization and relative abundance of insertions in pools of Tn mutants. The essentiality and fitness cost, in terms of growth advantage and disadvantage of over 105 mutants were quantitatively compared between in vitro and different stages of infection in two evolutionary distinct hosts, D. discoideum and BV2 microglial cells. We found that 57% of TA sites in the M. marinum genome were disrupted and that 568 genes (10.2%) are essential for M. marinum, which is comparable to previous Tn-Seq studies on M. tuberculosis. The major pathways involved in the survival of M. marinum during infection of D. discoideum were related to vitamin metabolism, the esx-1 operon, as well as the mce1 operon.

microbiology↗

bioRxiv2020

Intrathecal catheter implantation decreases cerebrospinal fluid dynamics in cynomolgus monkeys

A detailed understanding of the CSF dynamics is essential for testing and evaluation of intrathecal drug delivery. Preclinical work using large-animal models (e.g., monkeys, dogs and sheep) has great utility for defining spinal drug distribution/pharmacokinetics and provide an important tool for defining safety. In this study, we investigated the impact of catheter implantation in the sub-dural space on CSF flow dynamics in Cynomolgus monkeys. Magnetic resonance imaging (MRI) was performed before and after catheter implantation to quantify the differences based on catheter placement location in the cervical compared to the lumbar spine. Several geometric and hydrodynamic parameters were calculated based on the 3D segmentation and flow analysis. Hagen-Poiseuille equation was used to investigate the impact of catheter implantation on flow reduction and hydraulic resistance. A linear mixed-effects model was used in this study to investigate if there is a statistically significant difference between cervical and lumbar implantation, or between two MRI time points. Results showed that geometric parameters did not change statistically across MRI measurement time points and did not depend on catheter location. However, catheter insertion did have a significant impact on the hydrodynamic parameters and the effect was greater with the cervical implantation. CSF flow rate decreased up to 54.7% when the catheter located in the cervical region. The maximum flow rate reduction in the lumbar implantation group was 21%. Overall, lumbar catheter implantation disrupted CSF dynamics to a lesser degree than cervical catheter implantation and this effect remained up to two weeks post-catheter implantation

pharmacology and toxicology↗

bioRxiv2017

Translational control plays an important role in the adaptive heat-shock response of Streptomyces coelicolor

Stress-induced adaptations require multiple levels of regulation in all organisms to repair cellular damage. In the present study we evaluated the genome-wide transcriptional and translational changes following heat stress exposure in the soil-dwelling model actinomycete bacterium, Streptomyces coelicolor. The combined analysis revealed an unprecedented level of translational control of gene expression, deduced through polysome profiling, in addition to transcriptional changes. Our data show little correlation between the transcriptome and translatome; while an obvious downward trend in genome wide transcription was observed, polysome associated transcripts following heat-shock showed an opposite upward trend. A handful of key protein players, including the major molecular chaperones and proteases were highly induced at both the transcriptional and translational level following heat-shock, a phenomenon known as potentiation. Many other transcripts encoding cold-shock proteins, ABC-transporter systems, multiple transcription factors were more highly polysome-associated following heat stress; interestingly, these protein families were not induced at the transcriptional level and therefore were not previously identified as part of the stress response. Thus, stress coping mechanisms at the level of gene expression in this bacterium go well beyond the induction of a relatively small number of molecular chaperones and proteases in order to ensure cellular survival at non-physiological temperatures.

genomics↗