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Differences in Shewanella algae C6G3 transcriptomes according to nature of electron acceptor (MnIV/NO3)

ABSTRACT: Shewanella algae C6G3 can conduct dissimilative nitrate reduction into ammonium and MnIV reduction. This bacteria have the unusual ability to produce anaerobically nitrite from ammonium in the presence of MnIV. This property may explain NO2/3- accumulation observed in some anaerobic zones of marine sediments. To gain insight into their metabolic capabilities, global mRNA expression patterns were investigated by RNA-seq and qRT-PCR in cells growing with lactate and ammonium as carbon and nitrogen sources and with MnIV or nitrate as electron acceptors. Genes exhibiting higher expression levels in the presence of MnIV belonged to functional categories of carbohydrate, coenzyme, lipid metabolisms and inorganic ion transport. Furthermore, comparative transcriptomic pattern between MnIV and NO3 revealed that the strain presented an ammonium limitation status with MnIV, despite the presence of identical and non-limiting concentration of ammonium in both culture conditions. Regulators ntrB/nrtC, ammonium channel, nitrogen regulatory protein P-II, glutamine synthetase and asparagine synthetase glutamine dependent genes were over-expressed. In nitrate condition, genes involved in synthesis of several amino acids were over expressed. Among the genes associated with the stress response, Kat E was highly expressed particularly under manganese condition

ORGANISM(S): Shewanella algae

PROVIDER: GSE109146 | GEO | 2018/12/31

REPOSITORIES: GEO

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Project description:Algal biofuel production requires an input of synthetic nitrogen fertilizer. Fertilizer synthesized via the Haber-Bosch process produces CO2 as a waste by-product and represents a substantial financial and energy investment. Reliance on synthetic fertilizer attenuates the environmental significance and economic viability of algae production systems. To lower fertilizer input, the waste streams of algal production systems can be recycled to provide alternative sources of nitrogen such as amino acids to the algae. The halophytic green alga Dunaliella viridis can use ammonium (NH4+) derived from the abiotic degradation of amino acids, and previously, supplementation of NH4+ from glutamine (GLN) degradation was shown to support acceptable levels of growth and increased neutral lipid production compared to nitrate. To understand the effect of glutamine-released NH4+ on algae growth and physiology, metabolite levels, growth parameters, and transcript profiles of D. viridis cultures were observed in a time course after transition from media containing nitrate as a sole N source to medium containing GLN, glutamate (GLU), or a N-depleted medium. Growth parameters were similar between GLN (NH4+) and nitrate supplemented cultures, however, metabolite data showed that the GLN supplemented cultures (NH4+) more closely resembled cultures under nitrogen starvation (N-depleted and GLU supplementation). Neutral lipid accumulation was the same in nitrate and glutamine-derived NH4+ cultures. However, glutamine-derived NH4+ caused a transcriptional response in the immediate hours after inoculation of the culture. The strong initial response of cultures to NH4+ changed over the course of days to closely resemble that of nitrogen starvation. These observations suggest that release of NH4+ from glutamine was sufficient to maintain growth, but not high enough to trigger a cell transition to a nitrogen replete state. Comparative transcript profiling of the nitrogen-starved and nitrate-supplied cultures show an overall downregulation of fatty acid synthesis and a shift to starch synthesis and accumulation. The results indicate that a continuous, amino acid derived slow release of NH4+ to algae cultures could reduce the amount of synthetic nitrogen needed for growth, but optimization is needed to balance nitrogen starvation and cell division.

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Differences in Shewanella algae C6G3 transcriptomes according to nature of electron acceptor (MnIV/NO3)

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