Consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems. This is a new paradigm for many in geotechnical engineering. Realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification. This paper assesses the progress, opportunities, and challenges in this emerging field. Biomediated geochemical processes, which consist of a geochemical reaction regulated by subsurface microbiology, currently being explored include mineral precipitation, gas generation, biofilm formation and biopolymer generation. For each of these processes, subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals, organic matter, pore fluids, and gases that constitute soil. Geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radionuclides. Challenges in biomediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process, and education of engineers and researchers.

Among the environmental factors, soil salinity is one of the most detrimental factors affecting plant growth and productivity. Nutritional-imbalance is also known as one of the negative effects of salinity on plant growth and productivity. Among the essential plant nutrients, phosphorus (P) is a nutrient in which the uptake, transport, and distribution in plant is adversely affected by salinity-stress. Salinity-stress-mediated low a P availability limits the crop production. Adding additional P fertilizer is generally recommended to manage P deficit in saline-soils; however, the low-efficiency of available P fertilizer use in salt-affected soils, restricts P availability, and P fertilizers are also a cause of significant environmental concerns. The application of salinity-tolerant phosphate–solubilizing-bacteria (ST-PSB) can be as a greatly effective and economical way to improve the P availability, and recover the P-deficit in saline-land. This review focuses on soil salinization and its effect on P availability, the mechanisms of P solubilization by ST-PSB, ST-PSB diversity, their role in alleviating salinity stress in plants, the current and future scenarios of their use, and the potential application of this knowledge to manage the sustainable environmental system. According to this review, adding ST-PSB to saline soils could be an alternative for alleviating the negative effects of salinity on plants and may ameliorate salinity tolerance.

Biological synthesis of gold and silver nanoparticles was carried out using the bacteria Bacillus subtilis. The reduction processes of chloroaurate and silver ions by B. subtilis were found to be different. Gold nanoparticles were synthesized both intra- and extracellularly, while silver nanoparticles were exclusively formed extracellularly. The gold nanoparticles were formed after 1 day of addition of chloroaurate ions, while the silver nanoparticles were formed after 7 days. The nanoparticles were characterized by X-ray diffraction, UV-vis spectra and transmission electron spectroscopy. X-ray diffraction revealed the formation of face-centered cubic (fcc) crystalline gold nanoparticles in the supernatant, broth solution and bacterial pellet. Silver nanoparticles also exhibited diffraction peaks corresponding to fcc metallic silver. UV-vis spectra showed surface plasmon vibrations for gold and silver nanoparticles centered at 530 and 456 nm, respectively. TEM micrographs depicted the formation of gold nanoparticles intra- and extracellularly, which had an average size of 7.6 ± 1.8 and 7.3 ± 2.3 nm, respectively, while silver nanoparticles were exclusively formed extracellularly, with an average size of 6.1 ± 1.6 nm. The bacterial proteins were analyzed by sodium dodecyl sulfonate-polyacrylamide electrophoresis (SDS-PAGE) before and after the addition of metal ion solutions. We believe that proteins of a molecular weight between 25 and 66 kDa could be responsible for chloroaurate ions reduction, while the formation of silver nanoparticles can be attributed to proteins of a molecular weight between 66 and 116 kDa. We also believe that the nanoparticles were stabilized by the surface-active molecules i.e., surfactin or other biomolecules released into the solution by B. subtilis.

Improper disposal practices have caused environmental disruptions, possessing by heavy metal ions and radioactive elements in water and soil, where the innovative and sustainable remediation strategies are significantly imperative in last few decades. Microbially induced carbonate precipitation (MICP) has emerged as a pioneering technology for remediating contaminated soil and water. Generally, MICP employs urease-producing microorganisms to decompose urea (NH₂CONH₂) into ammonium (NH₄⁺and carbon dioxide (CO₂), thereby increasing pH levels and inducing carbonate precipitation (CO₃^2-), and effectively removing remove contaminants. Nonetheless, the intricate mechanism underlying heavy metal mineralization poses a significant challenge, constraining its application in contaminants engineering, particularly in the context of prolonged heavy metal leaching over time and its efficacy in adverse environmental conditions. This review provides a comprehensive idea of recent development of MICP and its application in environmental engineering, examining metabolic pathways, mineral precipitation mechanisms, and environmental factors as well as providing future perspectives for commercial utilization. The use of ureolytic bacteria in MICP demonstrates cost-efficiency, environmental compatibility, and successful pollutant abatement over tradition bioremediation techniques, and bio-synthesis of nanoparticles. limitations such as large-scale application, elevated Ca²⁺levels in groundwater, and gradual contaminant release need to be overcome. The possible future research directions for MICP technology, emphasizing its potential in conventional remediation, CO₂ sequestration, bio-material synthesis, and its role in reducing environmental impact for long-term economic benefits.