Optimization of factors influencing exopolysaccharide production by Halomonas xianhensis SUR308 under batch culture

Simultaneous conversion of chromium and malachite green coexists in halophilic bacterium Halomonas xianhensis SUR308 isolated from a solar saltern

Many industries are known to use heavy metals like chromium (Cr) to fix dyes in the fabrication processes and malachite green (MG) as colorant. Alkalinity, elevated temperature, or salinity of the industrial effluents makes conventional physicochemical removal of MG and hexavalent chromium [Cr(VI)] more difficult to apply and demands to perceive potential cost-effective and environment-friendly treatment methods to eliminate or convert them into less toxic compounds. Here, we report simultaneous removal and bioconversion of MG and Cr(VI) by a halophilic biofilm-forming bacterium Halomonas xianhensis SUR308. It can efficiently produce exopolysaccharides as extracellular polymeric substances (EPS) and form biofilm under oxygen limiting condition. The reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] is about 100%, and 95% after 84 h of growth in shaken and stagnant culture, respectively. The strain completely decolorizes MG after 48 h of growth in shaken culture. Furthermore, we found that strain SUR308 can efficiently detoxify chromium by reduction and degrades MG via producing various intermediate products simultaneously. Most interestingly, such conversions can also take place in alkaline environment and in environment where substantial amount of salt is present. These unique features of strain SUR308 make it suitable for the simultaneous remediation of toxic heavy metals and hazardous dye even from the environment having higher pH and salinity. The detail molecular mechanism of the bioconversion with its application in open environment would be the future research focus for bioprospecting strain SUR308.

Marine Microbial Polysaccharides: An Untapped Resource for Biotechnological Applications

As the largest habitat on Earth, the marine environment harbors various microorganisms of biotechnological potential. Indeed, microbial compounds, especially polysaccharides from marine species, have been attracting much attention for their applications within the medical, pharmaceutical, food, and other industries, with such interest largely stemming from the extensive structural and functional diversity displayed by these natural polymers. At the same time, the extreme conditions within the aquatic ecosystem (e.g., temperature, pH, salinity) may not only induce microorganisms to develop a unique metabolism but may also increase the likelihood of isolating novel polysaccharides with previously unreported characteristics. However, despite their potential, only a few microbial polysaccharides have actually reached the market, with even fewer being of marine origin. Through a synthesis of relevant literature, this review seeks to provide an overview of marine microbial polysaccharides, including their unique characteristics. In particular, their suitability for specific biotechnological applications and recent progress made will be highlighted before discussing the challenges that currently limit their study as well as their potential for wider applications. It is expected that this review will help to guide future research in the field of microbial polysaccharides, especially those of marine origin.

Assessing the effect of multiple variables on the production of bioflocculant by Serratia marcescens: Flocculating activity, kinetics, toxicity, and flocculation mechanism

Bioflocculants gain attention as alternatives to chemical flocculants because they are more environmentally friendly and highly biodegradable. This study aims to improve the bioflocculant production by Serratia marcescens using one-variable-at-a-time (OVAT) analysis and analyze its flocculating activity performance, toxicity, and the flocculation mechanism. The effect of multiple variables including initial inoculum size, pH, mixing speed, temperature, growth medium, and incubation period was assessed through OVAT. Flocculating activity was then determined via jar test analysis, and toxicity test was performed using Daphnia magna and Daphnia pulex. The flocculation mechanism was determined via particle size distribution and zeta potential analysis. The optimum conditions for the improved bioflocculant production were as follows: 10% v/v initial inoculum size, pH 7, mixing speed of 150 rpm, room temperature, nutrient broth medium, and 72 h of incubation period. Scanning electron microscopy showed flake-like intact structure with coarse surface. The produced bioflocculant showed flocculating activity of 48% in 5227 ± 580 NTU initial kaolin turbidity with 1 mg/L concentration and 5% v/v dosage of bioflocculant, following the second-order kinetics. Toxicity test to D. magna and D. pulex showed the 48 h LC₅₀ values of 8.06 and 6.42 g/L, respectively; these values are greatly higher than the fabricated chemical flocculants. The flocculation process using bioflocculant produced by S. marcescens was suggested to occur via bridging mechanism because it greatly affected the particle size distribution. Results indicated that bioflocculant produced by S. marcescens is much environmentally friendly and has great potential for turbidity removal in water/wastewater.

Extracellular Polysaccharide Extraction from Streptococcus thermophilus in Fermented Milk

Lactic acid bacteria such as Streptococcus thermophilus are known to produce extracellular polysaccharide (EPS) in fermented foods that enhance the creaminess and mouthfeel of the product, such as yogurt. Strains producing larger amounts of EPS are highly sought-after, and therefore, robust and accurate quantification methodologies are important. This study found that two commonly used methodologies significantly underestimated the amount of EPS produced as measured using a milk matrix. To this end, a proteolytic step was implemented prior to EPS extraction (Method C). An initial proteolytic step using xanthan gum-spiked milk significantly increased recovery yield to 64%, compared to 27.8% for Method A and 34.3% for Method B. Method C showed no improvement when assessed using a chemically defined medium. Method C was further validated using three strains of S. thermophilus with varying EPS-production capabilities (ST^LOW, ST^MID, ST^HIGH). Overall, Method C demonstrated significant improvements in the EPS extraction yield for all three S. thermophilus strains in fermented milk. On average, Method C improved isolation yield by ∼3- to 6-fold compared with Method A and by ∼2- to 3-fold compared with method B. There were no significant differences between samples when they were grown in a chemically defined medium, highlighting the importance of a proteolytic step specifically for fermented milk samples. In commercial applications, accurate quantification of EPS-production is an important aspect when finding new strains. IMPORTANCE Extracellular polysaccharide (EPS) production by milk-fermenting microorganisms is a highly sought-after trait in improving the perceived thickness, creaminess, and mouthfeel of yogurt. Streptococcus thermophilus are commonly isolated and their EPS production is quantified in the search for higher-producing strains. In this study, we demonstrated that two commonly used methods for isolating EPS from milk samples significantly underestimated the true amount of EPS present. We demonstrated that the addition of a proteolytic step prior to EPS extraction isolated over 2-fold more EPS than identical samples processed using the traditional protocols. We further validated this method in fermented milk samples from three strains of S. thermophilus that included a low-, mid-, and high-EPS producing strain. Again, we showed significant improvements in EPS isolation using a proteolytic step. In the search for new S. thermophilus strains with enhanced EPS production, accurate quantification in an optimal medium is essential.

Metabolic potential of the moderate halophile Yangia sp. ND199 for co-production of polyhydroxyalkanoates and exopolysaccharides

Yangia sp. ND199 is a moderately halophilic bacterium isolated from mangrove samples in Northern Vietnam, which was earlier reported to grow on several sugars and glycerol to accumulate poly(hydroxyalkanoates) (PHA). In this study, the potential of the bacterium for co‐production of exopolysaccharides (EPS) and PHA was investigated. Genome sequence analysis of the closely related Yangia sp. CCB‐M3 isolated from mangroves in Malaysia revealed genes encoding enzymes participating in different EPS biosynthetic pathways. The effects of various cultivation parameters on the production of EPS and PHA were studied. The highest level of EPS (288 mg/L) was achieved using sucrose and yeast extract with 5% NaCl and 120 mM phosphate salts but with modest PHA accumulation (32% of cell dry weight, 1.3 g/L). Growth on fructose yielded the highest PHA concentration (85% of CDW, 3.3 g/L) at 90 mM phosphate and higher molecular weight EPS at 251 mg/L yield at 120 mM phosphate concentration. Analysis of EPS showed a predominance of glucose, followed by fructose and galactose, and minor amounts of acidic sugars.

Genome analysis of a halophilic bacterium Halomonas malpeensis YU-PRIM-29T reveals its exopolysaccharide and pigment producing capabilities

Halomonas malpeensis strain YU-PRIM-29T is a yellow pigmented, exopolysaccharide (EPS) producing halophilic bacterium isolated from the coastal region. To understand the biosynthesis pathways involved in the EPS and pigment production, whole genome analysis was performed. The complete genome sequencing and the de novo assembly were carried out using Illumina sequencing and SPAdes genome assembler (ver 3.11.1) respectively followed by detailed genome annotation. The genome consists of 3,607,821 bp distributed in 18 contigs with 3337 protein coding genes and 53% of the annotated CDS are having putative functions. Gene annotation disclosed the presence of genes involved in ABC transporter-dependent pathway of EPS biosynthesis. As the ABC transporter-dependent pathway is also implicated in the capsular polysaccharide (CPS) biosynthesis, we employed extraction protocols for both EPS (from the culture supernatants) and CPS (from the cells) and found that the secreted polysaccharide i.e., EPS was predominant. The EPS showed good emulsifying activities against the petroleum hydrocarbons and its production was dependent on the carbon source supplied. The genome analysis also revealed genes involved in industrially important metabolites such as zeaxanthin pigment, ectoine and polyhydroxyalkanoate (PHA) biosynthesis. To confirm the genome data, we extracted these metabolites from the cultures and successfully identified them. The pigment extracted from the cells showed the distinct UV-Vis spectra having characteristic absorption peak of zeaxanthin (λmax 448 nm) with potent antioxidant activities. The ability of H. malpeensis strain YU-PRIM-29T to produce important biomolecules makes it an industrially important bacterium.

Production and Characterization of Extracellular Polymeric Substances by marine Halomonas sp. NASH isolated from Wadi El-Natroun

Halophilic micro-organisms often synthesize and produce extracellular polysaccharides (EPS), whose physical, chemical properties and material properties vary greatly from each other. The extracellular polysaccharide (EPS) development of Halomonas sp. MN795630 strain type halophilic bacterium (NASH) was investigated and whether biotechnological applications were feasible. After 168 hours of incubation, 4 g/L of EPS was produced and all elements from the medium were completely used during the growth. Sucrose has been identified as the most favorable carbon source for production of EPS and maximum production (6 g/l). Beef extract level was shown to be the best for EPS production among different nitrogen sources. Optimum production of EPS (10 g/L) were achieved by supplementing the medium with 4M NaCl, pH adjusted at 9 and the medium was inoculated with 7% initial inoculum. The purified EPS were characterized chemically. Fourier transform infrared (FTIR) spectrophotometer was observed in several functional groups. EPS also demonstrated an significant inhibitor of Candida albicans ATCC 10231 and Pseudomonas aeruginosa ATCC 9027 (20.4 and 14.7 mm), respectively. EPS show satisfactory results when applied as anti-oxidant, anti-inflammatory and emulsifier.

High bioreactor production and emulsifying activity of an unusual exopolymer by Chromohalobacter canadensis 28

Unusual composition of an exopolymer (EP) from an obligate halophilic bacterium Chromohalobacter canadensis 28 has triggered an interest in development of an effective bioreactor process for its production. Its synthesis was investigated in 2-L bioreactor at agitation speeds at interval 600-1000 rpm, at a constant air flow rate of 0.5 vvm; aeration rates of 0.5, 1.0, and 1.5 vvm were tested at constant agitation rate of 900 rpm. EP production was affected by both, agitation and aeration. As a result twofold increase of EP yield was observed and additionally increased up to 3.08 mg/mL in a presence of surfactants. For effective scale-up of bioreactors mass transfer parameters were estimated and lowest values of KLa obtained for the highest productivity fermentation was established. Emulsification activity of EP exceeded that of trade hydrocolloids xanthan, guar gum, and cellulose. A good synergism between EP and commercial cellulose proved its potential exploration as an enhancer of emulsifying properties of trade emulsions. A pronounced lipophilic effect of EP was established toward olive oil and liquid paraffin. Cultivation of human keratinocyte cells (HaCaT) with crude EP and purified γ-polyglutamic acid (PGA) showed higher viability than control group.

Potential antitumor activity of exopolysaccharide produced from date seed powder as a carbon source for Bacillus subtilis

The major functions of Exopolysaccharide (EPS) include, preventing bacterial cells from desiccating and biofilm production to increase the colonization of bacterial cells. In the current study, a bacterial strain was isolated to produce EPS. Phylogenetic analysis of the isolated strain indicated it was related to Bacillus subtilis. The bacterium showed the ability to produce a new EPS using very cheap date seeds as a carbon source. Different conditions were studied to enhance exopolysaccharide production. Maximum total sugars (exopolysaccharide) were reached to 0.87 mM) at 20 g/lAjwadates seed (ADS). The maximum production was found to be 3.46 mM by addition of peptone as the main source of nitrogen with a concentration of 1.5 g/L. The optimal parameter values were temperature 37 °C, pH 6, incubation time 72 h and inoculum concentration 1 mL. The crude exopolysaccharide was purified by removing the cells, then the protein, then dialysis and finally ethanol precipitation of the exopolysaccharide. This method modification increased exopolysaccharide production to 0.6 g/L. The exopolysaccharide produced showed antitumor activity against Erlich tumor cells. It is promising for application on a large scale for different types of cancer cell lines.