• Energy Research
• Open Access close
• Embargo close
• IN close
• FEMS Microbiology Letters close

In the thermophilic fungus Thermomyces lanuginosus, invertase displays an unusual pattern of development: the induced activity begins to diminish even before any substantial quantity of sucrose has been utilized or an appreciable amount of biomass has been produced. Despite this pattern of invertase activity, neither the growth rate nor the final mycelial yield is affected adversely. T. lanuginosus invertase is a thiol protein and the enzyme is active when specific sulfhydryl group(s) is in the reduced state. Measurements of reduced coenzyme and glutathione pools in sucrose-growth mycelia excluded oxidative stress as the primary reason for the observed decline in invertase activity. Rather, this unusual pattern of invertase is considered to be due to its localization in the hyphal tips. At the early stage of growth, the number of hyphal tips per unit mass of mycelium is maximum, whereas at later times their numbers do not increase in proportion to the biomass. As a result invertase activity shows an apparent inverse relationship with biomass. The enzyme activity disappears when the inducing carbon source is consumed and growth is completed.

This paper illustrates the application of an untargeted metabolic profiling analysis of winery-derived biomass degraded using four filamentous fungi (Trichoderma harzianum, Aspergillus niger, Penicillium chrysogenum and P. citrinum) and a yeast (Saccharomyces cerevisiae). Analysis of the metabolome resulted in the identification of 233 significant peak features [P 2 and signal-to-noise ratio >50] using gas chromatography-mass spectrometry followed by statistical chemometric analysis. Furthermore, A. niger and P. chrysogenum produced higher biomass degradation due to considerable β-glucosidase and xylanase activities. The major metabolites generated during fungal degradation which differentiated the metabolic profiles of fungi included sugars, sugar acids, organic acids and fatty acids. Although, P. chrysogenum could degrade hemicelluloses due to its high β-glucosidase and xylanase activities, it could not utilize the resultant pentoses, which A. niger and P. citrinum could do efficiently, thus indicating a need of mixed fungal culture to improve the biomass degradation. Saccharomyces cerevisiae, a non-cellulose degrader, exhibited sugar accumulation during the fermentation. Penicillium chrysogenum was observed to degrade about 2% lignin, a property not observed in other fungi. This study emphasized the differential fungal metabolic behavior and demonstrated the potential of metabolomics in optimizing degradation or manipulating pathways to increase yields of products of interest.

ABSTRACT Microbial fuel cells (MFCs) offer a promising solution towards recovery and treatment of heavy metal pollutants. In this study, two-chambered MFCs were employed for recovery of chromium, copper and vanadium (Cr (VI), Cu (II) and V (V)). One g/L concentrations of K2Cr2O7, CuCl2 and NaVO3 served as catholytes, while a mixed culture was used as anolyte. Cr (VI), Cu (II) and V (V) were reduced biologically into less toxic forms of Cr (III), Cu and V (IV) respectively. Power density and cathodic efficiency were calculated for each of the catholytes. Cr (VI) gave the maximum power density and cathodic efficiency due to its high redox potential. Current produced depended on the concentration of the catholyte. Over a period of time, biological reduction of catholytes lead to decrease in the metal concentrations, which demonstrated the application of MFC technology towards heavy metal treatment and recovery in a reasonably cost-effective manner.

Abstract Thermo-acidic pretreatment of lignocellulosic biomass is required to make it amenable to microbial metabolism and results in generation of furfural due to breakdown of pentose sugars. Furfural is toxic to microbial metabolism and results in reduced microbial productivity and increased production costs. This study asks if deletion of yghZ gene which encodes a NADPH-dependent aldehyde reductase enzyme results in improved furfural tolerance in Escherichia coli host. The ∆yghZ strain—SSK201–was tested for tolerance to furfural in presence of 5% xylose as a carbon source in AM1 minimal medium. At 96 h and in presence of 1.0 g/L furfural, the culture harboring strain SSK201 displayed 4.5-fold higher biomass, 2-fold lower furfural concentration and 15.75-fold higher specific growth rate (µ) as compared to the parent strain SSK42. The furfural tolerance advantage of SSK201 was retained when the carbon source was switched to glucose in AM1 medium and was lost in rich LB medium. The findings have potential to be scaled up to a hydrolysate culture medium, which contains furan inhibitors and lack nutritionally rich components, under bioreactor cultivation and observe growth advantage of the ∆yghZ host. It harbors potential to generate robust industrial strains which can convert lignocellulosic carbon into metabolites of interest in a cost-efficient manner.

The mechanism of adaptation of bacteria to survive at elevated temperature in the human host and the expression of heat-shock proteins in response to stress was examined by labelling with [35S]methionine. An increase in culture temperature from 26 degrees C to 37 degrees C induced expression of certain bacterial proteins (70 and 60 kDa). Heat shock at 40 degrees C, cold shock (10 degrees C), ethanol treatment or arsenite treatment also led to an increased expression of heat shock proteins of 70 and 60 kDa. Actinomycin D completely blocked the induction, indicating that transcription is required for the overexpression of stress proteins in Leuconostoc mesenteroides. N-terminal sequence analysis showed that these proteins were homologous to the highly conserved chaperone proteins DnaK and GroEL of Escherichia coli, respectively.

The chrysene-degrading bacterium Pseudoxanthomonas sp. PNK-04 was isolated from a coal sample. Three novel metabolites, hydroxyphenanthroic acid, 1-hydroxy-2-naphthoic acid and salicylic acid, were identified by TLC, HPLC and MS. Key enzyme activities, namely 1-hydroxy-2-naphthoate hydroxylase, 1,2-dihydroxynaphthalene dioxygenase, salicylaldehyde dehydrogenase and catechol-1,2-dioxygenase, were noted in the cell-free extract. These results suggest that chrysene is catabolized via hydroxyphenanthroic acid, 1-hydroxy-2-naphthoic acid, salicylic acid and catechol. The terminal aromatic metabolite, catechol, is then catabolized by catechol-1,2-dioxygenase to cis,cis-muconic acid, ultimately forming TCA cycle intermediates. Based on these studies, the proposed catabolic pathway for chrysene degradation by strain PNK-04 is chrysene → hydroxyphenanthroic acid → 1-hydroxy-2-naphthoic acid → 1,2-dihydroxynaphthalene → salicylic acid → catechol →cis,cis-muconic acid.

CO2 is a resource yet to be effectively utilized in the autotrophic biotechnology, not only to mitigate and moderate the anthropogenic influence on our climate, but also to steer CO2 sequestration for sustainable development and carbon neutral status. The atmospheric CO2 concentration has seen an exponential increase with the turn of the new millennia causing numerous environmental issues and also in a way feedstock crisis. To progressively regulate the growing CO2 concentrations and to incorporate the integration strategies to our existing CO2 capturing tools, all the influencing factors need to be collectively considered. The review article puts forth the change in perception of CO2 from which was once considered a harmful pollutant having deleterious effects to a renewable carbon source bearing the potential to replace the fossils as the carbon source through an autotrophic biorefinery. Here, we review the current methods employed for CO2 storage and capture, the need to develop sustainable methods and the ways of improving the sequestration efficiencies by various novice technologies. The review also provides an autotrophic biorefinery model with the potential to operate and produces a multitude of biobased products analogous to the petroleum refinery to establish a circular bioeconomy. Furthermore, fundamental and applied research niches that merit further research are delineated.

Anoxic ammonium oxidation (Anammox) and Completely Autotrophic Nitrogen removal Over Nitrite (CANON) are new and promising microbial processes to remove ammonia from wastewaters characterized by a low content of organic materials. These two processes were investigated on their feasibility and performance in a gas-lift reactor. The Anammox as well as the CANON process could be maintained easily in a gas-lift reactor, and very high N-conversion rates were achieved. An N-removal rate of 8.9 kg N (m(3) reactor)(-1) day(-1) was achieved for the Anammox process in a gas-lift reactor. N-removal rates of up to 1.5 kg N (m(3) reactor)(-1) day(-1) were achieved when the CANON process was operated. This removal rate was 20 times higher compared to the removal rates achieved in the laboratory previously. Fluorescence in situ hybridization showed that the biomass consisted of bacteria reacting to NEU, a 16S rRNA targeted probe specific for halotolerant and halophilic Nitrosomonads, and of bacteria reacting to Amx820, specific for planctomycetes capable of Anammox.

The effect of salt stress on ethanol endurance of yeast cells was studied. Cells grown under increased NaCl concentrations were more ethanol tolerant than controls. The increase in trehalose content under hyper-saline conditions has been suggested to allow cells to withstand higher ethanolic conditions. There seems to be an overlap between osmotolerance and ethanol endurance in Saccharomyces cerevisiae.