Aims: Rhamnolipids are seeking utmost attention as a new class of biosurfactants having promising potential in diverse fields as they offer a wide range of advantages over chemically synthesised surfactants. However, the high extraction costs make large scale production face difficulty. In present study, hydrocarbon degrading bacteria Pseudomonas aeruginosa UKMP14T was exploited for its biosurfactant producing ability including a comparative study between different extraction procedures for its recovery. In addition to this, the recovered biosurfactant was explored for its potential application as an antimicrobial agent. Methodology and results: The production of rhamnolipid biosurfactant was confirmed through various detection methods which are drop-collapse test, oil spreading assay, emulsification index, cetyltrimethylammonium bromide (CTAB) assay and hemolytic assay. The test strain P. aeruginosa UKMP14T showed positive results for all the detection assays. Following this, shake flask cultivation was carried out for several time intervals (1, 3, 5, 7 and 9 days) to discover the optimum time for rhamnolipid biosurfactant production. The results were evaluated by quantifying the rhamnolipid yield using Anthrone method and maximum yield was obtained on day 7. Then, three commonly employed rhamnolipid biosurfactant extraction methods (acid precipitation, solvent extraction and zinc sulphate precipitation) were incorporated for the extraction of rhamnolipid biosurfactant. Among these methods, organic solvent extraction (using methanol, chloroform and acetone in 1:1:1 ratio) gave the highest yield (7.37 ± 0.81 g/L) of biosurfactant, followed by zinc sulphate precipitation (5.83 ± 0.02 g/L), whereas acid precipitation gave the lowest yield (2.8 ± 0.12 g/L) and required longer time (30 days). Finally, the antimicrobial activity of several concentrations of rhamnolipid was tested using modified microdilution method and highest antibacterial activity (in the form of percent reduction in growth) of 95.05% and 91.89% was recorded for Escherichia coli ATCC 10536 and Staphylococcus aureus ATCC 11632, respectively, at 100 µg/mL concentration of rhamnolipid biosurfactant. Conclusion, significance and impact of study The ability of P. aeruginosa UKMP14T in producing rhamnolipid biosurfactant was confirmed. Despite the higher yield obtained by organic solvent extraction method, the recovery technique (involving the separation of solvent system) caused some loss in product. In addition, the transfer and storage of rhamnolipid was challenging using solvent extraction in comparison to acid precipitation and zinc sulphate precipitation. On the other hand, recovery using acid precipitation suffered from lowest yield of rhamnolipid. Therefore, zinc sulphate precipitation is prioritised over the other two methods. Furthermore, the antimicrobial potential of rhamnolipid biosurfactant was tested successfully for as low as 10 µg/mL concentration against E. coli ATCC 10536 and S. aureus ATCC 11632. Therefore, the recovery cost of a high value product like rhamnolipid can be reduced by incorporating the results of this study in the downstream processing and promote rhamnolipid biosurfactant as a potential antimicrobial agent.
Glycolipids--biosynthesis ; Surface-Active Agents ; Pseudomonas aeruginosa

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