This study aimed to examine the calcite precipitation potential of non-ureolytic bacterial strains of two species, Viridibacillus arenosi (A₆) and Bacillus zhangzhouensis (D₂₅), as compared to the known ureolytic bacterial strain, Sporosarcina pasteurii (SP), within geopolymer mortar. Tests were carried out after 56 days of injection treatment to confirm the precipitation process, incorporating healing efficiency measured by ImageJ software, recovery of UPV, water permeability, capillary water absorption, and microstructural and mineralogical analysis SEM/EDS and XRD. The non-ureolytic isolates D₂₅ and A₆ showed the highest healing efficiencies, at 96.9% and 91.9%, respectively, followed by the ureolytic bacteria SP at 77.8%. A₆ exhibited the most substantial reduction in permeability at 97.3%, indicating extensive crack healing, followed by D₂₅ at 92.9% and SP at 82.1%. Furthermore, SEM and EDS analyses confirmed the formation of calcite crystals and calcium depositions in the bacteria-treated samples. Complementary evidence was provided by XRD, which revealed distinct calcium carbonate peaks in the treated specimens, peaks that were entirely absent in the control samples, thus strongly confirming the role of bacterial activity in the precipitation process. The results confirm that non-ureolytic bacteria can efficiently boost calcite precipitation in geopolymer mortars, offering superior healing performance and a more sustainable alternative to ureolytic strains.

Microorganisms are distributed everywhere even on the extreme environments such as caves. The underground surfaces are minerals rich and the life in there is found to be related to both biotic and abiotic factors. Since the cycle of these minerals is insured by the chemolithotrophs living in there. In addition, caves are also considered as important reservoirs of bioactive compounds. However, caves are entered for different reasons. Some of cavers are of scientific research, some of them are for recreational reasons like sports and simple cave visits. All these activities are thought to impacts on the visible mat and invisible colonies of microorganisms through mechanical force or importing exogenous microorganisms. This study summarizes the different impacts which can be caused by the different human activities in caves. Finally, perspective of the conservation of cave microbial structure are suggested for the further uses of caves.

In this last decade, the environmental problems of microplastics have been occupied a large place in the world scientific researches. The unbreakable property of these particles causes their rapid accumulation in the environment. Their micro and millimetric sizes let them to be distributed over the world in a way almost uncontrollable. Works are still multiplying in identification of the source and nature, in the fate and effects of the microplastics on the different ecosystems. The accumulation of these debris in our ecosystem is a serious problem in the way of their distribution and migration: from the aquatic to the terrestrial ecosystem, all food web class will be affected. Different solutions for escaping their over distribution in the world have been studied. However, the biodegradation of this tiny particles seems the perfect solution of their disappearance from our environments. Studies seem slowly progressed because of different types of microplastics and the unknown mechanism of most of microorganisms on the surface of microplastics. This review is a synthesis of works done in microplastics by offering a good comprehension in microplastics source, effects and biodegradation both in aquatic and terrestrial ecosystems. Researchers will have to expand their working fields by approaching to the extreme ecosystems such as caves in the hope of finding microorganisms capable of producing enzymes that will serve in a complete degradation of these debris.

Abiotic and biotic factors, especially microorganisms, play a role in the development of cave formations and the existence of unique characteristics of each cave. Due to the ecological conditions that characterize the cave environments, highly specialized microorganisms that are the main source of diverse bioactive compounds, inhabit these environments. The aim of this study is to determine the role and biotechnological potential of the bacteria isolated from Yarık Sinkhole located in Antalya (Turkey) by screening their ability to induce the CaCO3 precipitation, to hydrolyze urea, to induce calcite dissolution, and screening their possession of NRPS/PKS gene clusters. The most prevalent phylum is the Bacillota (synonym Firmicutes) (75.7 %), while the dominant species is Bacillus pumilus (33 %). All the isolates showed crystal formation on B4 agar medium, and the Energy dispersive X-Ray spectroscopy (EDS) analyses showed that the crystals are predominately composed of calcium, carbon and oxygen. Ninety-six (96 %) of our isolates have negative ureolytic activity. According to this result and having the ability to induce the CaCO3 precipitation, bac­teria in this environment use other biosynthesis pathways than urea hydrolysis. MgCO3 and CaCO3 were dissolved by 61 % and 59 % of the isolates, respectively. In addition, 5.9 % and 53.7 % of the isolates showed the possession of PKS and NRPS genes, respectively. This result reveals that our isolates have high in­dustrial and biotechnological potential. They may constitute good candidates for further biotechnological applications such as construction of bio-concretes, bioremediation, soil fertility, and production of biologically active secondary metabolites.