Biology subjects

Provatas, A. A.

Publications and source records attributed to Provatas, A. A..

3 recordsLinked to original sources

bioRxiv2026

The MarR-family regulator TilR links biosynthesis of enterotoxin tilimycin with physiologic adaptation in Klebsiella oxytoca

Members of the Klebsiella oxytoca species complex (KoSC) are ubiquitous gut colonizers that produce the DNA-damaging enterotoxin tilimycin (TM) as part of their virulence-related program. A MarR-like transcriptional regulator, herein designated TilR, controls expression of the divergently transcribed aroX- and NRPS-operons responsible for TM production. Deletion of tilR resulted in pronounced induction of both operons, elevated toxin production, and increased cytotoxicity - establishing TilR as the key repressor of TM biosynthesis. TilR is encoded downstream of the NRPS operon and binds a 20 bp motif within the aroX-NRPS intergenic region, spatially separated from the predicted promoters driving toxin gene expression. Analysis of global transcriptome profiles revealed that TilR, the most highly expressed of the seven MarRs in KoSC, links toxin biosynthesis to a broader transcriptional network involved in nutrient acquisition, stress adaptation, and central metabolism. In addition, TM production coincided with induction of multiple virulence-associated genes involved in adhesion, biofilm formation, and iron acquisition. Phylogenetic and structural analyses revealed that TilR is distinct from canonical MarRs and absent from members of the closely related, competing Klebsiella pneumoniae species complex (KpSC). These findings identify TilR as an evolutionarily specialized global regulator that coordinates TM biosynthesis with broader metabolic, stress-adaptive, and virulence-associated transcriptional responses.

microbiology↗

bioRxiv2025

Wildfire ash impacts to photosynthesis and growth of marine phytoplankton cultures

Climate change includes increasing surface temperatures as well as extreme events--heatwaves, storms, floods, and droughts. In 2020, these factors produced a record 10,000 wildfires that burned 18,000 km2 in California USA. Air pollution, including airborne ash, from these fires was a widespread human health hazard. While the ecological effects of wildfires have been extensively documented in terrestrial and freshwater systems, impacts on ocean and coastal ecosystems are largely unexplored. Here, we describe the physical and chemical properties of ash from the CZU Lightning Complex fire and experimentally test its effects on the photosynthesis and growth of four unicellular marine phytoplankton. Sieved air-fall ash was primarily composed of particles 250-500 m and contained [~]1 {per thousand} of Fe, Mn, and Ba. Diagnostic indices of polycyclic aromatic hydrocarbons indicated the air-fall ash originated from combusted wood, and the total concentration of the EPA 16 high-priority PAHs exceeded 2.7 ppm. Pulse Amplitude Modulation fluorometry documented various declines in the photosynthetic efficiency of Isochrysis and Dunaliella cultures dosed with ash, and the bulk cellular growth of these cultures was inhibited. While our study demonstrated the impacts of wildfire ash on marine producers, the precise mechanisms are unclear. We provide recommendations for how future studies may further resolve the impacts of ash on phytoplankton productivity, community diversity, and trophic transfer of toxins and describe the long-term impacts of wildfires on coastal marine ecosystems.

ecology↗

bioRxiv2020

PREFERENTIAL SYNTHESIS OF VERY LONG CHAIN POLYUNSATURATED FATTY ACIDS IN EUTREPTIELLA SP. (EUGELNOZOA) REVEALED BY CHROMATOGRAPHIC AND TRANSCRIPTOMIC ANALYSES

Algal lipids are important fuel storage molecules in algae and a currency for energy transfer in the marine food chain as well as materials for biofuel production, but their production and regulation are not well understood in many species including the common coastal phytoplankton Eutreptiella spp. Here, using gas chromatography-tandem mass spectrometry (GC/MS/MS), we discovered 24 types of fatty acids (FAs) in Eutreptiella sp. with a relatively high proportion of long chain unsaturated FAs. The abundances of C16, C18 and saturated FAs decreased when phosphate in the culture medium was depleted. Among the 24 FAs, docosahexaenoic acid (22:6) and eicosapentaenoic acid (20:5) were the most abundant, suggesting that Eutreptiella sp. preferentially invests in the synthesis of very long chain polyunsaturated fatty acids (VLCPFA). Further transcriptomic analysis revealed that Eutreptiella sp. likely synthesizes VLCPFA via {Delta}8 pathway and uses type I and II fatty acid synthases. Using RT-qPCR, we found that some of the lipid production genes, such as {beta}-ketoacyl-ACP reductase, fatty acid desaturase, acetyl-CoA carboxylase, acyl carrier protein, {Delta}8 desaturase, and Acyl-ACP thioesterase, were more actively expressed during light period. Besides, two carbon-fixation genes were more highly expressed in the high lipid illuminated cultures, suggesting a linkage between photosynthesis and lipid production.

molecular biology↗