Extreme environments have been the interest of numerous studies and scientific publications. For many years, these environmental roles, which are characterised by high or low temperatures, high-pressure, low pH, high salt concentrations and companions of two or more extreme parameters. For many years, these environmental niches have increased in importance due to extreme microorganisms diversity and their potential returns of several industrial production processes concerning the food fields, medical and pharmaceutical. At present, it's possible to detect life in most extreme environments, from the deep sea hot springs, depth of the oceans, deep inside the earth crust, harsh chemical environments, and high radiation environments through metagenomics analysis. In this review, newly identified microorganisms, and their potential uses in several applied fields have been outlined. The microbial development in biofilms form has supported the survival of alkaliphiles, psychrophile, halophile thermophile and extremophile microorganisms; where they flourish due to the adaptation strategies involving complex variation in biofilms structure and behaviours.

Aims: Dental caries is a chronic infectious disease caused by Streptococcus mutans due to its ability to form biofilm. This study aims to assess the antimicrobial efficacy of Melastoma malabathricum leaf extract against S. mutans on the surface of tooth samples as a potential therapy for dental caries. Methodology and results: Extraction of M. malabathricum leaves was done using acetone as the solvent and antibacterial activity of the extracts was determined by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Antibiofilm activity of M. malabathricum extract against S. mutans was determined by comparing the colony count, biofilm formation assay and morphology observation by scanning electron microscope (SEM). The MIC value of extracts was 6.25 mg/mL and MBC value was >25 mg/mL. A decrease in colony count was noted when tooth samples were incubated with M. malabathricum extract for 8 h compared to 4 h incubation. At pH 5, the formation of the colony was the least, medium at pH 8 and maximum at pH 7. A decrease in biofilm formation was observed when tooth samples were incubated with the extract for 8 h. SEM observations showed treatment with the extract caused S. mutans cell membrane to leak leading to cell morphology changes. Conclusion, significance and impact of study Acetone extract of M. malabathricum leaves showed excellent antibacterial activity against S. mutans. It has bactericidal activity with the ability to inhibit biofilm in dose-dependent manner against S. mutans. The morphological analyses suggested that the extract disrupted the cell membrane of the bacteria.
Dental Caries--therapy