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The archaeon Pyrococcus furiosus is emerging as a metabolic engineering platform for production of fuels and chemicals, such that more must be known about this organism's characteristics in bioprocessing contexts. Its ability to grow at temperatures from 70 to greater than 100°C and thereby avoid contamination, offers the opportunity for long duration, continuous bioprocesses as an alternative to batch systems. Toward that end, we analyzed the transcriptome of P. furiosus to reveal its metabolic state during different growth modes that are relevant to bioprocessing. As cells progressed from exponential to stationary phase in batch cultures, genes involved in biosynthetic pathways important to replacing diminishing supplies of key nutrients and genes responsible for the onset of stress responses were up-regulated. In contrast, during continuous culture, the progression to higher dilution rates down-regulated many biosynthetic processes as nutrient supplies were increased. Most interesting was the contrast between batch exponential phase and continuous culture at comparable growth rates (∼0.4 hr−1), where over 200 genes were differentially transcribed, indicating among other things, N-limitation in the chemostat and the onset of oxidative stress. The results here suggest that cellular processes involved in carbon and electron flux in P. furiosus were significantly impacted by growth mode, phase and rate, factors that need to be taken into account when developing successful metabolic engineering strategies. [ABSTRACT FROM AUTHOR]

Quorum sensing provides the basis for coordinating community-wide, microbial behaviors in many mesophilic bacteria. However, little attention has been directed toward the possibility that such phenomena occur in extremely thermal microbial environments. Despite the absence of luxS in hyperthermophile genomes, autoinducer-2 (AI-2), a boronated furanone and proposed ‘universal’ interspecies mesophilic bacterial communication signal, could be formed by Thermotoga maritima and Pyrococcus furiosus through a combination of biotic and abiotic reaction steps. AI-2 did not, however, induce any detectable quorum-sensing phenotypes in these organisms, although transcriptome-based evidence of an AI-2-induced stress response was observed in T. maritima. The significance, if any, of AI-2 in hydrothermal habitats is not yet clear. Nevertheless, these results show the importance of considering environmental factors, in this case high temperatures, as abiotic causative agents of biochemical and microbiological phenomena. [ABSTRACT FROM AUTHOR]

Abstract: Hydrothermal microbiotopes are characterized by the consumption and production of molecular hydrogen. Heterotrophic hyperthermophilic microorganisms (growth T opt⩾80°C) actively participate in the production of H2 in these environments through the fermentation of peptides and carbohydrates. Hyperthermophiles have been shown to approach the theoretical (Thauer) limit of 4mol of H2 produced per mole of glucose equivalent consumed, albeit at lower volumetric productivities than observed for mesophilic bacteria, especially enterics and clostridia. Potential advantages for biohydrogen production at elevated temperatures include fewer metabolic byproducts formed, absence of catabolic repression for growth on heterogeneous biomass substrates, and reduced loss of H2 through conversion to H2S and CH4 by mesophilic consortia containing sulfate reducers and methanogens. To fully exploit the use of these novel microorganisms and their constituent hydrogenases for biohydrogen production, development of versatile genetic systems and improvements in current understanding of electron flux from fermentable substrates to H2 in hyperthermophiles are needed. [Copyright &y& Elsevier]