High synthetic cost-amino acids reduce member interactions of acetate-degrading methanogenic microbial community.

Introduction: The cooperation among members of microbial communities based on the exchange of public goods such as 20 protein amino acids (AAs) has attracted widespread attention. However, little is known about how AAs availability affects interactions among members of complex microbial communities and the structure and function of a community. Methods: To investigate this question, trace amounts of AAs combinations with different synthetic costs (low-cost, medium-cost, high-cost, and all 20 AAs) were supplemented separately to acetate-degrading thermophilic methanogenic reactors, and the differences in microbial community structure and co-occurring networks of main members were compared to a control reactor without AA supplementation. Results: The structure of the microbial community and the interaction of community members were influenced by AAs supplementation and the AAs with different synthetic costs had different impacts. The number of nodes, links, positive links, and the average degree of nodes in the co-occurrence network of the microbial communities with AAs supplementation was significantly lower than that of the control without AAs supplementation, especially for all 20 AAs supplementation followed by the medium- and high-cost AAs supplementation. The average proportion of positive interactions of microbial members in the systems supplemented with low-cost, medium-cost, high-cost, all AAs, and the control group were 0.42, 0.38, 0.15, 0.4, and 0.45, respectively. In addition, the ecological functions of community members possibly changed with the supplementation of different cost AAs. Discussion: These findings highlight the effects of AAs availability on the interactions among members of complex microbial communities, as well as on community function.

Evaluation of physicochemical properties, bacterial community, and product fertility during rice straw composting supplemented with different nitrogen-rich wastes.

This study evaluated the compostability of rice straw as the main feedstock (75 % in dry weight), supplemented with three different nitrogen-rich wastes, namely food waste (FW), dairy manure (DM), and sewage sludge (SS). Organic matter (OM) degradation, maturity and fertility of the end-product, and bacterial community structure during the composting processes were compared. All composting processes generated mature end-product within 51 days. Notably, FW addition was more effective to accelerate rice straw OM degradation and significantly improved end-product fertility with a high yield of Chinese cabbage. The succession of the bacterial community was accelerated with FW supplementation. Genera Geobacillus, Chryseolinea, and Blastocatella were significantly enriched during the composting of rice straw with FW supplementation. Finally, temperature, total nitrogen, moisture, pH, and total carbon were the key factors affecting microorganisms. This study provides a promising alternative method to enhance the disposal of larger amounts of rice straw in a shorter time.

Microbial communities in crude oil phase and filter-graded aqueous phase from a Daqing oilfield after polymer flooding.

AIMS: The aim was to characterize indigenous micro-organisms in oil reservoirs after polymer flooding (RAPF). METHODS: The microbial communities in the crude oil phase (Oil) and in the filter-graded aqueous phases Aqu0.22 (>0.22 µm) and Aqu0.1 (0.1-0.22 µm) were investigated by 16S rRNA gene high-throughput sequencing. RESULTS: Indigenous micro-organisms related to hydrocarbon degradation prevailed in the three phases of each well. However, obvious differences in bacterial compositions were observed amongst the three phases of the same well and amongst the same phase of different wells. The crude oil and Aqu0.22 shared many dominant bacteria. Aqu0.1 contained a unique bacterial community in each well. Most bacteria in Aqu0.1 were affiliated to culturable genera, suggesting that they may adapt to the oil reservoir environment by reduction of cell size. Contrary to the bacterial genera, archaeal genera were similar in the three phases but varied in relative abundances. The observed microbial differences may be driven by specific environmental factors in each oil well. CONCLUSIONS: The results suggest an application potential of microbial enhanced oil recovery (MEOR) technology in RAPF. The crude oil and Aqu0.1 contain many different functional micro-organisms related to hydrocarbon degradation. Both should not be overlooked when investing and exploring the indigenous micro-organisms for MEOR. SIGNIFICANCE AND IMPACT OF THE STUDY: This work facilitates the understanding of microbial community structures in RAPF and provides information for microbial control in oil fields.

The Comparison of Structural, Physicochemical, and Digestibility Properties of Repeatedly and Continuously Annealed Sweet Potato Starch.

In order to investigate the varied effects of repeated annealing treatment (RANN) and continuous annealing treatment (CANN) on the structural, physicochemical, and digestibility properties of the sweet potato. The 75% starch-water suspensions were prepared and incubated at 65 °C for 8 cycles and 96 hr. The results exhibited that RANN and CANN did not influence the starch granules and polarization cross obviously. The crystal type of RANN and CANN starches still maintained A-type, while the relative crystallinity increased. The solubility, swelling power, peak viscosity and breakdown of RANN and CANN starches decreased, but the gelatinization transition temperatures, trough viscosity, final viscosity, setback, and pasting temperatures of starches increased after annealing treatments. Furthermore, RANN and CANN decreased the RS and RS + SDS contents with the increase of annealing cycles and time. The RANN was more effective in modification of the crystallinity, solubility, swelling power, pasting, gelatinization transition temperatures and enthalpy, and digestibility of starch before four times compared with the CANN ones. By and large, RANN may be a potential way for modification of structural, physicochemical and digestibility properties. PRACTICAL APPLICATION: The described RANN and CANN starch provide new ideas for the study of modified starch. Furthermore, this study revealed the mechanism of annealing treatment and it was concluded that the repeated annealing treatment could provide a new potential way for the modification of starch.

Physical and structural properties of potato starch modified by dielectric treatment with different moisture content.

The altered morphology, amylose content, microstructure, viscosity and thermal properties of potato starch after heating by radio frequency (RF) and microwaves (MW) were studied and contrasted with the native potato starch. The results showed that the MW treatment roughens the starch surface and lowers the amylose content of the starch, even more than the RF-treated starch does. The starch granule size of MW treated was larger than RF treated. RF treatment altered the structure and reduced the crystallinity of the starch, but the MW treatment did not affect the crystal form. The gelatinization temperature of the MW-treated starch was higher than the native potato starch, while the RF-treated starch was lower than the native starch. The results also indicated that the peak viscosity and the breakdown viscosity values of the RF-treated starch consistently surpassed that of the MW-treated starch. The results exposed the facts that RF treated starch showed the same trend on crystal and pasting properties compared with the hot water annealing starches, which suggested RF can be an efficient method for starch annealing.

The effect of repeated versus continuous annealing on structural, physicochemical, and digestive properties of potato starch.

Native potato starch was suspended in distilled water at starch: water ratio of 1:3 (w/v). The starch-water suspensions were then subjected to repeated annealing treatments (RANN) at 55 °C for 12 h, repeated for 8 cycles or continuous annealing treatments (CANN) at 55 °C for 24, 48, 72 and 96 h. The structural, physiochemical and digestive properties of the annealed starch samples were studied and compared with those of the native starch. The scanning electron microscopy and light microscopy analysis showed that the repeated and continuous annealing treatments could keep the integrity and surface perfection of the starch granules. The growth rings of the annealed starch granules were more distinct than those of the native starch granules as revealed by confocal laser scanning microscopy. The crystallinity degree increased and the crystalline retained the B-type pattern after the annealing treatments. There were no chemical bonds and functional groups produced or disappeared during the applied annealing treatments. Infrared absorption peak intensity of starch decreased and short-range ordered structures increased after treatments. The swelling power and solubility decreased at low temperature (50 to 60 °C) and increased at relatively high temperature (70 to 90 °C). The rapid visco-analyzer and differential scanning calorimeter analysis revealed an increase in the setback, final viscosity, pasting temperature and gelatinization transition temperature, and a decrease in breakdown value of the starch after the annealing treatments. On the other hand, the repeated and continuous annealing treatments resulted in starch with low in vitro digestibility degree, indicating formation of resistant starch. Generally, the repeated annealing treatment resulted in starch with high improved properties compared with the starch resulted from the continuous annealing treatments. Therefore, the repeated annealing treatments can be suggested as an effective method for producing of modified starch for food industrial applications.