Stancheva, R. | Search bioRxiv

bioRxiv2026

Predicting taxon-specific benthic cyanobacterial mat cover and anatoxin concentrations in northern California rivers

Ecological forecasts often rely on established relationships between the ecological process of interest and predictor variables that are more easily measured. Proliferations of benthic (i.e., bottom-dwelling) cyanobacteria have been increasingly observed in rivers globally and are an emerging ecological forecasting issue as they pose a public health threat due to the production of potent neurotoxins known as anatoxins. Controls on these benthic cyanobacteria are poorly understood, thus predicting or forecasting their extent and anatoxin production is a significant challenge. Here, we measured benthic cyanobacterial cover and anatoxin concentrations for two common taxa associated with anatoxins (Microcoleus and Anabaena) at biweekly to weekly intervals during June to September in 2022 and 2023 in three northern Californian rivers. We then built predictive models to test how incorporation of a biotic predictor (river reach-scale gross primary productivity [GPP]) affected predictive accuracy in addition to widely measured abiotic predictors (i.e., nutrients, discharge, and temperature). Temporal patterns in taxon-specific benthic cyanobacterial cover and anatoxin concentrations were highly variable among rivers and between taxa. While Microcoleus cover peaked in rivers during periods of relatively low GPP, there were no clear relationships between GPP and Anabaena cover nor anatoxin concentrations of either taxon among rivers. Among multiple reaches sampled weekly in the South Fork Eel River, magnitudes of taxon-specific benthic cyanobacterial cover and anatoxin concentrations differed, but the timing of peak taxon-specific cover and anatoxin concentrations were generally consistent. Furthermore, Anabaena displayed a hysteresis relationship where increases in cover were followed by increases in anatoxin concentrations while Microcoleus lacked such relationship. While incorporating GPP as a covariate improved our predictions of Anabaena cover, we had more success predicting Microcoleus cover than Anabaena cover due to its strong negative relationship with discharge. In contrast, our models predicting Anabaena anatoxin concentrations outperformed those predicting Microcoleus anatoxin concentrations due to the hysteresis relationship between Anabaena cover and anatoxins. Overall, our predictive modeling results highlight the application of ecological forecasting for benthic cyanobacterial cover and anatoxin concentrations in rivers and demonstrate the importance of incorporating taxon-specific predictors into future forecasts of benthic cyanobacteria.

ecology↗

bioRxiv2023

Characterizing the microbial metagenome of calcareous stromatolite formations in the San Felipe Creek in Anza Borrego Desert

Here we describe the metagenome composition, community functional annotation, and diversity of prokaryotic microbial species derived from calcareous stromatolite formations discovered in the dry stream bed of the open-canopy, ephemeral San Felipe Creek in the Anza Borrego Desert. In this environment, resident microbes must be able to adapt to the harsh conditions of extreme heat, high UV light, desiccation and fluctuating solubilization/precipitation and hydration/evaporation. Metagenomic analysis revealed a community capable of carrying out complete nitrogen fixation and assimilatory nitrate reduction, forming biofilms and quorum sensing, and potentially forming thick-walled akinetes as desiccation-resistant stages. Nitrogen cycling is likely to play a fundamental role in mediating both the structure of the stromatolite microbial community and the mineral precipitation/dissolution. The viruses present in the stromatolites, particularly Nodularia and Mycobacterium phages are also likely to impact community population dynamics and activity. Stromatolite community members possess different morphological and physiological strategies to cope with desiccation stress. Metagenomic signatures were found for scytonemin, carotenoids, synthesis of potential microsporine-like amino acids; genes involved in microalgal desiccation tolerance, including those encoding aquaporins, chaperones, antioxidants; and enzymes responsible for the synthesis of trehalose, sucrose, and polyamines. The stromatolite ecosystem provides a diverse array of microniches where different functional guilds can develop complex metabolite exchange with the substrate supporting their life in extreme conditions. Metagenome analyses revealed several genes that might enable a specialized and unique group of endolithic cyanobacteria including Chroococcidiopsis, Hyella, Myxosarcina, and Pleurocapsa to derive metals and important nutrients from rocks, being potentially destructive for the calcareous formations. Our study revealed environmental adaptations of freshwater microbial communities in desert stream stromatolites which may provide valuable insights into Precambrian paleoenvironments, which are little known.

genomics↗