Biology subjects

Grzymski, J. J.

Publications and source records attributed to Grzymski, J. J..

4 recordsLinked to original sources

bioRxiv2018

Resource limitation modulates the fate of dissimilated nitrogen in a dual-pathway Actinobacterium

Respiratory ammonification and denitrification are two evolutionarily unrelated dissimilatory nitrogen (N) processes central to the global N cycle, the activity of which is thought to be controlled by carbon (C) to nitrate (NO3-) ratio. Here we find that Intrasporangium calvum C5, a novel menaquinone-based dual-pathway denitrifier/respiratory ammonifier, disproportionately utilizes ammonification rather than denitrification when grown under carbon or nitrate limitation, not C:NO3- ratio. Higher growth rates are promoted by ammonification and metabolite and transcriptional profiles during growth show that the bacterium produces its own formate from a fermentable carbon source (lactate) to further generate a proton motive force for the ammonification pathway. Transcript abundances encoding for nitrite reducing enzymes, NrfAH and NirK, also significantly increase in response to nitrite production. Mechanistically, our results suggest that pathway selection is driven by intracellular redox potential (redox poise), which may be lowered during resource limitation, thereby decreasing catalytic activity of upstream electron transport steps needed for denitrification enzymes. Our work advances our understanding of the biogeochemical flexibility of N-cycling organisms and pathway evolution.

microbiology↗

bioRxiv2018

Physiological and transcriptional response of the diatom Corethron hystrix under robust UVR irradiation

The effect of ultraviolet radiation (UVR) on photosynthetic efficiency and the resulting mechanisms against UV exposure employed by phytoplankton are not completely understood. To address this knowledge gap, we developed a novel close-coupled, wavelength-configurable platform designed to produce precise and repeatable in vitro irradiation of Corethron hystrix, a member of a genera found abundantly in the Southern Ocean where UV exposure is high. We aimed to determine its metabolic, protective, mutative, and repair mechanisms as a function of varying levels of specific electromagnetic energy. Our results show that the physiological responses to each energy level of UV have a negative linear decrease in the photosynthetic efficiency of photosystem II proportional to UV intensity, corresponding to a large increase in the turnover time of quinone re-oxidation. Gene expression changes of photosystem II related reaction center proteins D1, CP43 and CP47 showed coordinated downregulation whereas the central metabolic pathway demonstrated mixed expression of up and downregulated transcripts after UVR exposure. These results suggest that while UVR may damage photosynthetic machinery, oxidative damage may limit production of new photosynthetic and electron transport complexes as a result of UVR exposure.

microbiology↗

bioRxiv2018

The Healthy Nevada Project: rapid recruitment for population health study

BackgroundNevada ranks in the bottom half of overall health rankings in the United States. The majority of residents of Northern Nevada live in Washoe County, which is confounded with high age-adjusted death rates for heart disease, cancer and chronic lower respiratory disease.\n\nMethodsSaliva as a source of DNA was collected from adults in Northern Nevada as the first phase of a much larger (100,000 participants) effort to contribute to comprehensive population health studies in Nevada. The personal genetics company 23andMe was used to genotype the first 10,250 participants and deliver their custom ancestry, traits, wellness, and carrier status reports.\n\nResultsThe study was announced by Governor Brian Sandoval on September 15, 2016 and within two days the registration of 9,700 volunteers for an appointment was complete. Processing of 9,344 participants was achieved in 3 months, with a no-show rate of just over 11%. The participant population was skewed to female and was less racially diverse than the population.\n\nConclusionDNA genotyping was administered free-of-charge and the patient population was representative of the socio-economic diversity in northern Nevada - indicating that free genetic testing is of interest to a broad swath of the population and a powerful motivator for comprehensive population health study research.

scientific communication and education↗

bioRxiv2016

Nitrogen cost minimization is promoted by structural changes in the transcriptome of N deprived Prochlorococcus cells

Prochlorococcus is a globally abundant marine cyanobacterium with many adaptations that reduce cellular nutrient requirements, facilitating growth in its nutrient-poor environment. One such genomic adaptation is the preferential utilization of amino acids containing fewer N-atoms, which minimizes cellular nitrogen requirements. We predicted that transcriptional regulation might be used to further reduce cellular N budgets during transient N limitation. To explore this, we compared transcription start sites (TSSs) in Prochlorococcus MED4 under N-deprived and N-replete conditions. Of 64 genes with primary and internal TSSs in both conditions, N-deprived cells initiated transcription downstream of primary TSSs more frequently than N-replete cells. Additionally, 117 genes with only an internal TSS demonstrated increased internal transcription under N-deprivation. These shortened transcripts encode predicted proteins with ~5-20% less N content compared to full-length transcripts. We hypothesized that low translation rates, which afford greater control over protein abundances, would be beneficial to relatively slow-growing organisms like Prochlorococcus. Consistent with this idea, we found that Prochlorococcus exhibits greater usage of glycine-glycine motifs, which cause translational pausing, when compared to faster growing microbes. Our findings indicate that structural changes occur within the Prochlorococcus MED4 transcriptome during N-deprivation, potentially altering the size and structure of proteins expressed under nutrient limitation.

genomics↗