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Bacteria and yeast are being intensively used to produce biofuels and high-added-value products by using plant biomass derivatives as substrates. The number of microorganisms available for industrial processes is increasing thanks to biotechnological improvements to enhance their productivity and yield through microbial metabolic engineering and laboratory evolution. This is allowing the traditional industrial processes for biofuel production, which included multiple steps, to be improved through the consolidation of single-step processes, reducing the time of the global process, and increasing the yield and operational conditions in terms of the desired products. Engineered microorganisms are now capable of using feedstocks that they were unable to process before their modification, opening broader possibilities for establishing new markets in places where biomass is available. This review discusses metabolic engineering approaches that have been used to improve the microbial processing of biomass to convert the plant feedstock into fuels. Metabolically engineered microorganisms (MEMs) such as bacteria, yeasts, and microalgae are described, highlighting their performance and the biotechnological tools that were used to modify them. Finally, some examples of patents related to the MEMs are mentioned in order to contextualize their current industrial use.

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In recent years, biodiesel production has emerged as an option for renewable and green fuel generation due to the constant reduction of fossil fuel reservoirs. Biofuels as biodiesel also show valuable attributes, environmentally speaking, due to their low environmental impact, contributing to the achievement of sustainability. However, costs are not allowable for large-scale production. Thereby, several novel processes have been proposed (e.g., reactive distillation) to solve this issue. An inconvenience for the development of these processes is the little information in the literature about the critical properties of fatty acids, which are precursors of biodiesel. Determination of critical properties for fatty acids through experimentation is difficult. The reason is that fatty acids tend to self-associate (to dimerize) due to carboxylic groups presence through hydrogen bonds, and consequently, have higher boiling points than other compounds of similar molecular mass (e.g., hydrocarbons, esters). Therefore, alternative methods for this determination are required. One choice is the group-contribution method, which is based on the structure of the molecule; however, results can significantly vary among different group-contribution approaches. Another alternative (and the focus of this research) for the determination of these properties is molecular simulation techniques. In this work, the liquid-vapor equilibrium as a function of temperature and the surface tension of three pure fatty acids of long chain (linoleic, oleic, and palmitic acid) have been calculated. Simulations have been performed by molecular dynamics using the method of direct determination of phase coexistence with the software GROMACS; in which the transferable potentials for phase equilibria united atom forcefield (TraPPE-UA) have been implemented for these specific molecules. Orthobaric densities and surface tension values have been reported at temperatures near the critical point (from 650 K to 800 K). Critical properties (temperature, pressure, density) have been extrapolated from trajectories obtained in these simulations using scaling law relations. Critical properties for these compounds are not available experimentally, therefore, group contribution calculations from the literature were used as a reference. In this comparison, the palmitic acid properties calculated in this work, show the best agreement among the three substances investigated.

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Mole sauce is one of the traditional Mexican foods; it is a complex mixture of ingredients of diverse origins that directly influence its nutritional value. The objective of this study was to investigate the antioxidant properties and nutritional components in five varieties of mole from Hidalgo in Mexico namely verde (V), ranchero (R), almendrado (A), casero (C), and pipian (P). Proximal chemical analysis and determination of the color index and the content of total starch, dietary fiber, mineral content (Ca, Na, K, and Mg), total phenolic content, and antioxidant activity by ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (2,2-diphenylpicrylhydrazyl) were carried out. All the five varieties of mole reported less than 25% moisture content while fat content varied from 42.9% to 58.25%. The color index ranged from a deep orange to a deep red color. A fair percentage of dietary fiber was found in all mole varieties with a low amount of starch as well. The presence of mostly insoluble dietary fiber, high phenolic content (36.13-79.49 mg GAE/100 g), and high antioxidant activity could be considered important strengths to boost the consumption of these traditional preparations. This research will contribute to a better scientific knowledge of traditional Mexican sauces as functional foods or nutraceuticals that could be used to avoid health disorders.

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In this article, the geographical location and availability of the most important crop residues generated in Mexico over the last 10 years (2008-2017) were determined. This study estimates the gross number of residues for the four most important cultivars in Mexico named conventional residues (CRs) such as corn, wheat, sorghum, and barley, and estimates were also made for regionally important crops identified as nonconventional residues (NCRs) such as coffee, sugarcane, and beans. The total and sustainable energy potentials (TEP and SEP) for agricultural residues were calculated, in similar way the butanol and electricity production potentials were also calculated if these residues were processed under a nonconventional biorefinery scheme; the calculated availability of crop residues was 59,059,666 t/year, thus demonstrating that Mexico could have great potential for bioenergy production. The estimated TEP was 1,787,241,249 PJ/year, and the SEP was 78,724,689 PJ/year. The production of butanol and its production cost were calculated for the main crop residues; the butanol volume ranged from 7348 to 161,610 t/day, and the volume of crops of regional importance ranged from 6461.9 to 151,389 t/day. The minimum butanol production cost was 2000 t/day of feedstock. The surplus electricity was determined for all crop residues.

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Background: The application of polycyclic aromatic hydrocarbons (PAHs) will affect the bacterial community structure as some groups will be favoured and others not. An alkaline saline soil with electrolytic conductivity (EC) 56 dS m-1 was spiked with anthracene and acetone while their effect on bacterial community structure was investigated. Results: The percentages of Acidobacteria and Actinobacteria decreased over time, while the percentage of Proteobacteria, mostly Xanthomonadales, increased. The percentage of the phylotypes belonging to the Nocardioides, Rhodococcus and Streptomyces, known degraders of PAHs, was larger in the anthracene-amended soil than in the acetone-amended and unamended soil at day 14. The phylotypes belonging to the genera Sphingomonas, also a known degrader of PAHs, however, was lower. Weighted and unweighted PCoA with UniFrac indicated that phylotypes were similar in the different treatments at day 0, but changed at day 1. After 14 days, phylotypes in the unamended and acetone-amended soil were similar, but different from those in the anthracene-spiked soil. Conclusions: It was found that incubating the soil and contaminating it with anthracene changed the bacterial community structure, but spiking the soil with acetone had little or no effect on the bacterial community structure compared to the unamended soil.

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In a previous study, remediation of anthracene from soil was faster in the top 0-2 cm layer than in the lower soil layers. It was not clear whether this faster decrease was due to biotic or abiotic processes. Anthracene-contaminated soil columns were covered with black or transparent perforated polyethylene so that aeration occurred but that fluctuations in water content were minimal and light could reach (LIGHT treatment) or not reach the soil surface (DARK treatment), or left uncovered so that soil water content fluctuate and light reached the soil surface (OPEN treatment). The amount of anthracene, microbial biomass C, and microbial activity as reflected by the amount of CO(2) produced within 3 days were determined in the 0-2 cm, 2-8 cm, and 8-15 cm layer after 0, 3, 7, 14, and 28 days. In the 0-2 cm layer of the OPEN treatment, 17% anthracene remained, 48% in the LIGHT treatment and 61% in the DARK treatment after 28 days. In the 2-8 cm and 8-15 cm layer, treatment had no significant effect on the dissipation of anthracene from soil after 14 and 28 days. It was found that light and fluctuations in water content stimulated the removal of anthracene from the top 0-2 cm soil layer, but not from the lower soil layers. It can be speculated that covering contaminated soil or piling it up will inhibit the dissipation of the contaminant.

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