Enhancement of harvesting efficiency and polyunsaturated fatty acid-rich lipid production of Aurantiochytrium sp. SW1 by co-cultivation with oleaginous fungus Cunninghamella bainieri 2A1

Aims@#Thraustochytrids have been shown to be excellent lipid producers due to their ability to accumulate over 50% lipid (g/g biomass) containing up to 50% docosahexaenoic acid (DHA). However, efficient and cost-effective cell recovery of lipid-rich biomass has become a significant challenge at the industrial scale. In this study, we attempted to enhance the harvesting efficiency (HE) and the DHA content of Aurantiochytrium sp. through co-cultivation with a γ-linolenic acid (GLA)-producing oleaginous filamentous fungus, Cunninghamella bainieri 2A1.@*Methodology and results@#A 72 h old C. bainieri 2A1 culture in the form of loose mycelia or pellets of various sizes was added into 72 h old Aurantiochytrium sp. cultures and further incubated for 48 h. The HE of Aurantiochytrium sp. was then determined by comparing the remaining OD values of the supernatant with and without minimal centrifugation at 4000× g. Results showed that 63.23% of HE was achieved without centrifugation from co-cultivation with dispersed mycelia. Higher HE between 96.71-99.55% was achieved when centrifugation was implemented, with the highest value resulting from co-cultivation with dispersed mycelia. These are higher than HE of centrifuged control cultures (80%) consisting of Aurantiochytrium sp. monocultures, suggesting that co-cultivation with C. bainieri 2A1 facilitates the recovery of Aurantiochytrium sp. cells. Moreover, the co-cultivation also resulted in a 28% increase in DHA compared to non-optimized cultures.@*Conclusion, significance and impact of study@#This study provides the first evidence of enhancement in harvesting and DHA content of oleaginous thraustochytrids that could be achieved through co-cultivation with oleaginous fungi.

Extraction and antimicrobial activity of rhamnolipid biosurfactant produced by Pseudomonas aeruginosa UKMP14T

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.

Antibacterial and antibiofilm analyses of Melastoma malabathricum leaves extract against Streptococcus mutans on tooth surfaces

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.

Bacterial isolation of oral, rectum and anus swabs from Macaca fascicularis and Macaca namestrina in Kemasul, Pahang, Malaysia

Abstract@#This study was conducted with the aim of isolating and identifying pathogenic bacterial communities from actively shedding anatomical sites of Macaca fascicularis and M. namestrina in Jambu Rias (JR) and Chemomoi (CM) in Kemasul Forest Reserve, Pahang and to determine the antibiotic susceptibility of these isolates. The findings show that M. fascicularis had higher bacterial density and ten different isolates were identified from these samples. The antibiotic susceptibility tests determined that ciproflaxin and vancomycin as most effective antibiotic towards these isolates.

Transcriptomic profiling of substrate-dependent autoaggregation in Pseudomonas putida CP1

Aims@#Pseudomonas putida CP1 is an interesting environmental isolate which exhibits substrate-dependent autoaggregation when the organism was grown on 0.5% (w/v) fructose. Autoaggregation is a process of a single bacterial species to develop clumps of cells during a substrate stress. This study was carried out to investigate the genetic changes in the bacterium during aggregate formation. @*Methodology and results@#P. putida CP1 was grown on 0.5% (w/v) fructose in batch culture at 30 °C and 150 rpm. The removal of fructose from the medium corresponded with aggregation of the cells which started after 8 h incubation. Microarray gene expression profiling using a P. putida KT2440 Genome Oligonucleotide Array (Progenika, Spain) showed that 838 genes involved in metabolism and adaptation were differentially expressed in P. putida CP1. Global transcriptomic profiling studies showed that P. putida CP1 growing on fructose resulted in the induction of genes encoding for proteins mainly involved in protein translation, ABC transporters, oxidative phosphorylation and two-component systems (TCS). Novel genes, associated with autoaggregation, were identified using transcriptomic analysis involved in ABC transporter, TCS, flagella assembly and lipopolysaccharide biosynthesis. It was also associated with the up-regulation of genes involved in the flagellar assembly including the fliE gene which encodes for the flagellar hook-basal body protein. @*Conclusion, significance and impact of study@#The identification of new genes involved in autoaggregation formation is important to understand the molecular basis of strain variation and the mechanisms implicated in cell-cell communication.

Extreme environment: Biofilms and microbial diversity

@#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.

Influences of extracellular polymeric substances (EPS) for autoaggregation of Pseudomonas putida CP1 during growth on mono-chlorophenol

Aims: Pseudomonas putida CP1 exhibits substrate-dependent autoaggregation during the degradation of 100 ppm 2- chlorophenol, 100 ppm 3-chlorophenol and 200 ppm 4-chlorophenol. This study discussed the production of extracellular polymeric substances (EPS) by the organism for the formation of aggregates. Methodology and results: Aggregation was accompanied by the production of extracellular polymeric substances (EPS). The extent of EPS production and the size of the aggregates increased with increasing stress as did the aggregation index and the hydrophobicity of the cells. A biochemical analysis of the EPS showed that the main constituents were carbohydrate (40% w/v) and protein (50% w/v) together with lower levels of DNA (<10% w/v). Conclusion, significance and impact study: Given that the aggregated form of the bacterium has shown potential for use in bioaugmentation, an in-depth understanding of the phenomenon could enhance the use of this organism in biological wastewater treatment systems.

Antibacterial and biofilm inhibition activities of Melastoma malabathricum stem bark extract against Streptococcus mutants

Aim: This study was to determine the antibacterial activity of Melastoma malabathricum stem bark acetone extract (MMSBAE) against Streptococcus mutans. Methodology and results: Antibacterial activity of the extract was determined by minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), biofilm formation, adherence inhibition, time kill studies and effect on S. mutans membrane integrity. MIC and MBC values of MMSBAE were 1.25 and 5 mg/mL, respectively. Time kill studies showed that reduction of colony forming unit in treated cells is 3 log10 after 10 h of treatment (p ˂ 0.05). The extracts reduced 50% biofilm and adherence activity of S. mutans at 1.88 mg/mL. The effect on S. mutans membrane integrity after exposure to MMSBAE for 90 and 120 min was determined by measuring leakage of cell content at 2 different wavelengths of 260 nm and 280 nm. In leakage assay, the percentage of absorbance (260 nm) in treated cell material showed 57% at 90 min and 60% at 120 min which is higher than negative control (<20%) but less than positive control (100%). The percentage absorbance of treated cell material (280 nm) was 61% at 90 min and 63% at 120 min. Identification of compound in MMSBAE was done by gas chromatography mass spectrometry (GCMS). Ten compounds were identified in the MMSBAE with some of them important in antimicrobial activity such as ethyl ester, undecene, and gamma sitosterol. Conclusion, significance and impact of study: MMSBAE showed excellent bactericidal and antibacterial activities against S. mutans. The antibacterial mode of action of MMSBAE is suggested to be the disruption of the S. mutans membrane structure. The MMSBAE significantly inhibited biofilm and adherence activities of S. mutans in dose dependent manner (p ˂ 0.05). MMSBAE has potential in the development of antibacterial agent with anti-biofilm and anti-adherence activities.