Screening biosurfactant-producing actinomycetes: Identification of Streptomyces sp. RP1 as a potent species for bioremediation

This study aimed to isolate biosurfactant-producing and hydrocarbon-degrading actinomycetes from different soils using glycerol-asparagine and starch-casein media with an antifungal agent. The glycerol-asparagine agar exhibited the highest number of actinomycetes, with a white, low-opacity medium supporting pigment production and high growth. Biosurfactant analyses, such as drop collapse, oil displacement, emulsification, tributyrin agar test, and surface tension measurement, were conducted. Out of 25 positive isolates, seven could utilize both olive oil and black oil for biosurfactant production, and only isolate RP1 could produce biosurfactant when grown in constrained conditions with black oil as the sole carbon source and inducer, demonstrating in situ bioremediation potential. Isolate RP1 from oil-spilled garden soil is Gram-staining-positive with a distinct earthy odor, melanin formation, and white filamentous colonies. It has a molecular size of ~621 bp and 100% sequence similarity to many Streptomyces spp. Morphological, biochemical, and 16 S rRNA analysis confirmed it as Streptomyces sp. RP1, showing positive results in all screenings, including high emulsification activity against kerosene (27.2%) and engine oil (95.8%), oil displacement efficiency against crude oil (7.45 cm), and a significant reduction in surface tension (56.7 dynes/cm). Streptomyces sp. RP1 can utilize citrate as a carbon source, tolerate sodium chloride, resist lysozyme, degrade petroleum hydrocarbons, and produce biosurfactant at 37°C in a 15 mL medium culture, indicating great potential for bioremediation and various downstream industrial applications with optimization.

Extended Biosynthesis of Rhamnolipid by Immobilized Pseudomonas aeruginosa USM-AR2 Cells in a Fluidized Bed Bioreactor

This study aims to evaluate rhamnolipid production by immobilized Pseudomonas aeruginosa USM-AR2 cells using waste cooking oil (WCO) as the carbon source. P. aeruginosa USM-AR2 cells were entrapped in polyvinyl alcohol (PVA)-alginate hydrogel beads. The performance of entrapped cells was compared with free cells in shake flasks before cultivation in a custom-designed fluidized bed reactor (FBR). A mass of 1 g wet cells entrapped in PVA-alginate hydrogel beads were successfully recycled 3 times in shake flasks at 200 rpm, producing between 0.66-1.34 g L-1 rhamnolipid after 120 h. Meanwhile, cultivation of entrapped cells in FBR with broth recirculation showed that the suitable hydrogel beads to medium ratio was 1:20 ratio at an aeration rate of 0.5 vvm, producing between 0.77 to 1.58 g L-1 rhamnolipid, degrading 8.67 to 20.93 g L-1 of waste cooking oil in 15 cycles of repeated batch cultivation. Entrapped P. aeruginosa USM-AR2 cells achieved a higher rhamnolipid production, by 1.03-fold during cycle 3 in shake flasks and 1.19-fold during cycle 11 in an FBR, compared to free cells. These results show that entrapment enables reusability of viable cells and maintains stability of rhamnolipid production throughout the extended cultivation, increasing cell tolerance to perturbations in fermentation conditions.

Production of lipopeptide biosurfactant in batch and fed-batch Streptomyces sp. PBD-410L cultures growing on palm oil

The present study focused on lipopeptide biosurfactant production by Streptomyces sp. PBD-410L in batch and fed-batch fermentation in a 3-L stirred-tank reactor (STR) using palm oil as a sole carbon source. In batch cultivation, the impact of bioprocessing parameters, namely aeration rate and agitation speed, was studied to improve biomass growth and lipopeptide biosurfactant production. The maximum oil spreading technique (OST) result (45 mm) which corresponds to 3.74 g/L of biosurfactant produced, was attained when the culture was agitated at 200 rpm and aeration rate of 0.5 vvm. The best aeration rate and agitation speed obtained from the batch cultivation was adopted in the fed-batch cultivation using DO-stat feeding strategy to further improve the lipopeptide biosurfactant production. The lipopeptide biosurfactant production was enhanced from 3.74 to 5.32 g/L via fed-batch fermentation mode at an initial feed rate of 0.6 mL/h compared to that in batch cultivation. This is the first report on the employment of fed-batch cultivation on the production of biosurfactant by genus Streptomyces.

Colorimetric Analysis of Glucose Oxidase-Magnetic Cellulose Nanocrystals (CNCs) for Glucose Detection

Glucose oxidase (EC 1.1.3.4) sensors that have been developed and widely used for glucose monitoring have generally relied on electrochemical principle. In this study, the potential use of colorimetric method for glucose detection utilizing glucose oxidase-magnetic cellulose nanocrystals (CNCs) is explored. Magnetic cellulose nanocrystals (magnetic CNCs) were fabricated using iron oxide nanoparticles (IONPs) and cellulose nanocrystals (CNCs) via electrostatic self-assembly technique. Glucose oxidase was successfully immobilized on magnetic CNCs using carbodiimide-coupling reaction. About 33% of GOx was successfully attached on magnetic CNCs, and the affinity of GOx-magnetic CNCs to glucose molecules was slightly higher than free enzymes. Furthermore, immobilization does not affect the specificity of GOx-magnetic CNCs towards glucose and can detect glucose from 0.25 mM to 2.5 mM. Apart from that, GOx-magnetic CNCs stored at 4 °C for 4 weeks retained 70% of its initial activity and can be recycled for at least ten consecutive cycles.

Enhanced rhamnolipid production by Pseudomonas aeruginosa USM-AR2 via fed-batch cultivation based on maximum substrate uptake rate

A fed-batch strategy was established based on the maximum substrate uptake rate (MSUR) of Pseudomonas aeruginosa USM-AR2 grown in diesel to produce rhamnolipid. This strategy matches the substrate feed rates with the substrate demand based on the real-time measurements of dissolved oxygen (DO). The MSUR was estimated by determining the time required for consumption of a known amount of diesel. The MSUR trend paralleled the biomass profile of Ps. aeruginosa USM-AR2, where the MSUR increased throughout the exponential phase indicating active substrate utilization and then decreased when cells entered stationary phase. Rhamnolipid yield on diesel was enhanced from 0·047 (g/g) in batch to 0·110 (g/g) in pulse-pause fed-batch and 0·123 (g/g) in MSUR fed-batch. Rhamnolipid yield on biomass was also improved from 0·421 (g/g) in batch, 3·098 (g/g) in pulse-pause fed-batch to 3·471 (g/g) using MSUR-based strategy. Volumetric productivity increased from 0·029 g l(-1) h(-1) in batch, 0·054 g l(-1) h(-1) in pulse-pause fed-batch to 0·076 g l(-1) h(-1) in MSUR fed-batch.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study highlights the significance of an effective fed-batch strategy for rhamnolipid production in a submerged fermentation using a water-immiscible substrate, based on maximum substrate uptake rate. The impact of this strategy ensured that the substrate was supplied at the rate matching the maximum substrate utilization by the cells without excess feeding, leading to increased rhamnolipid production, yield and productivity.

Rhamnolipid produced by Pseudomonas aeruginosa USM-AR2 facilitates crude oil distillation

A biosurfactant-producing and hydrocarbon-utilizing bacterium, Pseudomonas aeruginosa USM-AR2, was used to assist conventional distillation. Batch cultivation in a bioreactor gave a biomass of 9.4 g L(-1) and rhamnolipid concentration of 2.4 g L(-1) achieved after 72 h. Biosurfactant activity (rhamnolipid) was detected by the orcinol assay, emulsification index and drop collapse test. Pretreatment of crude oil TK-1 and AG-2 with a culture of P. aeruginosa USM-AR2 that contains rhamnolipid was proven to facilitate the distillation process by reducing the duration without reducing the quality of petroleum distillate. It showed a potential in reducing the duration of the distillation process, with at least 2- to 3-fold decreases in distillation time. This is supported by GC-MS analysis of the distillate where there was no difference between compounds detected in distillate obtained from treated or untreated crude oil. Calorimetric tests showed the calorie value of the distillate remained the same with or without treatment. These two factors confirmed that the quality of the distillate was not compromised and the incubation process by the microbial culture did not over-degrade the oil. The rhamnolipid produced by this culture was the main factor that enhanced the distillation performance, which is related to the emulsification of hydrocarbon chains in the crude oil. This biotreatment may play an important role to improve the existing conventional refinery and distillation process. Reducing the distillation times by pretreating the crude oil with a natural biosynthetic product translates to energy and cost savings in producing petroleum products.

Biosynthesis of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer by Cupriavidus sp. USMAA1020 isolated from Lake Kulim, Malaysia

Cupriavidus sp. USMAA1020 was isolated from Malaysian environment and able to synthesize poly(3-hydroxybutyrate-co-4-hydroxybutyrate), [P(3HB-co-4HB)] when grown on gamma-butyrolactone as the sole carbon source. The polyester was purified from freeze-dried cells and analyzed by nuclear magnetic resonance (NMR) spectroscopy. 1H and 13C NMR results confirmed the presence of 3HB and 4HB monomers. In a one-step cultivation process, P(3HB-co-4HB) accumulation by Cupriavidus sp. USMAA1020 was affected by carbon to nitrogen ratio (C/N). A two-step cultivation process accumulated P(3HB-co-4HB) copolyester with a higher 4HB fraction (53 mol%) in nitrogen-free mineral medium containing gamma-butyrolactone. The biosynthesis of P(3HB-co-4HB) was also achieved by using 4-hydroxybutyric acid and alkanediol as 1,4-butanediol. The composition of copolyesters varied from 32 to 51 mol% 4HB, depending on the carbon sources supplied. The copolyester produced by Cupriavidus sp. USMAA1020 has a random sequence distribution of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) units when analyzed by nuclear magnetic resonance (NMR) spectroscopy. When gamma-butyrolactone was used as the sole carbon source, the 4HB fraction in copolyester increased from 25 to 60 mol% as the concentration of gamma-butyrolactone in the culture medium increased from 2.5 g/L to 20.0 g/L.