Application of stereolithographic custom models for studying the impact of biofilms and mineral precipitation on fluid flow

Years of sand fixation with Caragana korshinskii drive the enrichment of its rhizosphere functional microbes by accumulating soil N

C. korshinskii is one of the most widely-planted sand-fixing legumes in northwest China and exploring its rhizosphere microbiome is of great ecological importance. However, the effect of long-term sand fixation on the composition, diversity, and underlying functions of microbes in the C. korshinskii rhizosphere in dryland ecosystems remain unclear. Here, we performed high-throughput sequencing using a 16S rRNA (absolute quantification) and bacterial functional annotation of prokaryotic taxa (FAPROTAX) analysis and an ITS (relative quantification) and fungal functional guild (FUNGuild) analysis to investigate the C. korshinskii rhizosphere microbiome and metabolic functional groups at different sand-fixing ages (six years, CK6; twelve years, CK12; and eighteen years, CK18) and determined the physicochemical properties of the rhizosphere soil. Results showed that the key bacterial taxa of the rhizosphere were significantly more abundant in CK18 than in CK12 and CK6 at the phylum-class-genus level, and that fungal Glomeromycota was also significantly more abundant in the CK18 rhizosphere compared to CK12 and CK6. Among these bacterial taxa, the enrichment effect of key, functional, genus-level species of bacteria was the most obvious, including Rhizobium, Ensifer, Neorhizobium, Mesorhizobium, Streptomyces, Sphingomonas, and Flavobacterium, which are N-fixing and/or phosphate-solubilizing groups. The significant improvement seen in the physicochemical properties of the CK18 rhizosphere soil, including the higher total nitrogen (TN), available nitrogen (AN), pH, electrical conductivity (EC), higher N:P ratio, and lower C:N ratio, all demonstrated the relationship between the rhizosphere microbes and soil carbon (C) and nitrogen (N) cycling. A redundancy analysis (RDA) of different taxonomic levels indicated a close positive relationship between rhizosphere microbes and AN. In addition, the functional groups of the C. korshinskii rhizosphere bacteria were closely related to soil AN and were mainly composed of chemoheterotrophy and aerobic chemoheterotrophy. A Spearman correlation analysis revealed that these functional groups were mainly identified from bacterial Actinobacteria, Proteobacteria, Verrucomicrobia, Bacteroidetes, and fungal Glomeromycota. Our study provides evidence that the rhizosphere microbes of C. korshinskii are closely related to the accumulation of N in the restoration of desert ecosystems, and that the ecological functional processes they are involved in mainly involve C and N cycles, which play an important role in desertification reversal.

Sporosarcina pasteurii can clog and strengthen a porous medium mimic

The bacterium Sporosarcina pasteurii can produce significant volumes of solid precipitation in the presence of specific chemical environments. These solid precipitate particles can enter a network of microscale pores and cause long-range clogging. As a result, the medium gains strength and exhibits superior mechanical properties. This concept is also known as Microbiologically Induced Calcite Precipitation (MICP). In this study, we have used sponge blocks as surrogate porous media mimics and analyzed several aspects of MICP. A synergistic approach involving electron microscopy (SEM), computerized X-Ray tomography (μCT), quasi-static compressive load testing and chemical characterization (EDX) has been used to understand several physical and chemical aspects of MICP.

Applications of Microbial Processes in Geotechnical Engineering

Over the last 10-15 years, a new field of "biogeotechnics" has emerged as geotechnical engineers seek to find ground improvement technologies which have the potential to be lower carbon, more ecologically friendly, and more cost-effective than existing practices. This review summarizes the developments which have occurred in this new field, outlining in particular the microbial processes which have been shown to be most promising for altering the hydraulic and mechanical responses of soils and rocks. Much of the research effort in this new field has been focused on microbially induced carbonate precipitation (MICP) via ureolysis, while a comprehensive review of MICP is presented here, the developments which have been made regarding other microbial processes, including MICP via denitrification and biogenic gas generation are also presented. Furthermore, this review outlines a new area of study: the potential deployment of fungi in geotechnical applications which has until now been unexplored.

A new stereolithography experimental porous flow device

A new method for constructing laboratory-scale porous media with increased pore-level variabilities for two-phase flow experiments is presented here. These devices have been created with stereolithography directly on glass, thus improving the stability of the model created with this precision rapid construction technique. The method of construction and improved parameters are discussed in detail, followed by a brief comparison of two-phase drainage results for air invasion into the water-saturated porous medium. Flow through the model porous medium is shown to substantiate theoretical fractal predictions.