Characterization of esterase activity from an Acetomicrobium hydrogeniformans enzyme with high structural stability in extreme conditions

The biotechnological and industrial uses of thermostable and organic solvent-tolerant enzymes are extensive and the investigation of such enzymes from microbiota present in oil reservoirs is a promising approach. Searching sequence databases for esterases from such microbiota, we have identified in silico a potentially secreted esterase from Acetomicrobium hydrogeniformans, named AhEst. The recombinant enzyme was produced in E. coli to be used in biochemical and biophysical characterization studies. AhEst presented hydrolytic activity on short-acyl-chain p-nitrophenyl ester substrates. AhEst activity was high and stable in temperatures up to 75 °C. Interestingly, high salt concentration induced a significant increase of catalytic activity. AhEst still retained ~ 50% of its activity in 30% concentration of several organic solvents. Synchrotron radiation circular dichroism and fluorescence spectroscopies confirmed that AhEst displays high structural stability in extreme conditions of temperature, salinity, and organic solvents. The enzyme is a good emulsifier agent and is able to partially reverse the wettability of an oil-wet carbonate substrate, making it of potential interest for use in enhanced oil recovery. All the traits observed in AhEst make it an interesting candidate for many industrial applications, such as those in which a significant hydrolytic activity at high temperatures is required

Development and characterization of stable anaerobic thermophilic methanogenic microbiomes fermenting switchgrass at decreasing residence times

Background: Anaerobic fermentation of lignocellulose occurs in both natural and managed environments, and is an essential part of the carbon cycle as well as a promising route to sustainable production of fuels and chemicals. Lignocellulose solubilization by mixed microbiomes is important in these contexts. Results: Here, we report the development of stable switchgrass-fermenting enrichment cultures maintained at various residence times and moderately high (55 degrees C) temperatures. Anaerobic microbiomes derived from a digester inoculum were incubated at 55 degrees C and fed semi-continuously with medium containing 30 g/L mid-season harvested switchgrass to achieve residence times (RT) of 20, 10, 5, and 3.3 days. Stable, time-invariant cellulolytic methanogenic cultures with minimal accumulation of organic acids were achieved for all RTs. Fractional carbohydrate solubilization was 0.711, 0.654, 0.581 and 0.538 at RT = 20, 10, 5 and 3.3 days, respectively, and glucan solubilization was proportional to xylan solubilization at all RTs. The rate of solubilization was described well by the equation r = k(C -C(0)f(r)), where C represents the concentration of unutilized carbohydrate, C-0 is the concentration of carbohydrate (cellulose and hemicellulose) entering the bioreactor and f(r) is the extrapolated fraction of entering carbohydrate that is recalcitrant at infinite residence time. The 3.3 day RT is among the shortest RT reported for stable thermophilic, methanogenic digestion of a lignocellulosic feedstock. 16S rDNA phylotyping and metagenomic analyses were conducted to characterize the effect of RT on community dynamics and to infer functional roles in the switchgrass to biogas conversion to the various microbial taxa. Firmicutes were the dominant phylum, increasing in relative abundance from 54 to 96% as RT decreased. A Clostridium clariflavum strain with genetic markers for xylose metabolism was the most abundant lignocellulose-solubilizing bacterium. A Thermotogae (Defluviitoga tunisiensis) was the most abundant bacterium in switchgrass digesters at RT = 20 days but decreased in abundance at lower RTs as did multiple Chloroflexi. Synergistetes and Euryarchaeota were present at roughly constant levels over the range of RTs examined. Conclusions: A system was developed in which stable methanogenic steady-states were readily obtained with a particulate biomass feedstock, mid-season switchgrass, at laboratory (1 L) scale. Characterization of the extent and rate of carbohydrate solubilization in combination with 16S rDNA and metagenomic sequencing provides a multidimensional view of performance, species composition, glycoside hydrolases, and metabolic function with varying residence time. These results provide a point of reference and guidance for future studies and organism development efforts involving defined cultures

Environmental change and out-migration: evidence from Nepal

Scholars and activists have hypothesized a connection between environmental change and out-migration. In this paper we test this hypothesis using data from Nepal. We operationalize environmental change in terms of declining land cover, rising times required to gather organic inputs, increasing population density, and perceived declines in agricultural productivity. In general, environmental change is more strongly related to short- than long-distance moves. Holding constant the effects of other social and economic variables, we find that local moves are predicted by perceived declines in productivity, declining land cover, and increasing time required to gather firewood. Long-distance moves are predicted by perceived declines in productivity, but the effect is weaker than in the model of short-distance mobility. We also show that effects of environmental change vary by gender and ethnicity, with women being more affected by changes in the time required to gather fodder and men by changes in the time to gather firewood, and high caste Hindus generally being less affect than others by environmental change