Methylene blue is a toxic dye present in the textile industry, and if left untreated, it causes harm to the environment. Therefore, to decolorize methylene blue from industrial effluents, a green approach using Rhodococcus pyridinivorans strain UCC 0003 was attempted. Methylene blue decolorization was measured spectro-photometrically, and the static condition yielded 86% decolorization after 24 h as compared to the shaking mode (20%). Optimization of static conditions using the one-factor-at-a-time approach resulted in 100% decolorization at 30°C, pH 6, inoculum size of 16% (v/v), and 5% (v/v) banana peel addition as a carbon source. The R. pyridinivorans strain UCC 0003 could successfully and completely decolorize 0.75 g/l methylene blue for 4 consecutive cycles, which is advantageous from an economic point of view. The rate of methylene blue disappearance was investigated using 10% (v/v) R. pyridinivorans strain UCC 0003 at 30°C over a certain incubation time with 0.4 g/l to 10.0 g/l methylene blue as the substrate. This study revealed Vmax and Km values of 37.04 g/l/h and 55.69 g/l, respectively, as the kinetic behavior of methylene blue-decolorizing enzymes from the bacterial strain. The properties of the treated solution of methylene blue resembled the control system (distilled water) for the phytotoxicity study, thereby indicating the complete removal of dye toxicity as evidenced by the growth of Vigna radiata and Triticum aestivum, respectively, in the treated methylene blue solution. This local bacterial strain has therefore a huge potential to be used as a green biocatalyst for the bioremediation of methylene blue-containing industrial effluents.
In the present study, locally isolated Rhodococcus strains were attempted as biological tools for methyl red removal, a mutagenic azo dye posing threat to the environment if left untreated. Rhodococcus strain UCC 0016 demonstrated superior methyl red-decolourizing activity of 100% after 24 h at static condition in comparison to Rhodococcus strain UCC 0008 which recorded 65% decolourization after 72 h. Optimization of physicochemical parameters at 30°C, pH 7 and supplementing glucose as the carbon source resulted in improved methyl red-decolourizing activity at static condition and reduced the time taken to achieve complete decolourization by 80%. Higher concentration of methyl red (5 g/L) was able to be decolourized completely within 10 h by adopting the technology of immobilization. The encapsulated cells of Rhodococcus strain UCC 0016 demonstrated higher substrate affinity (Km = 0.6995 g/L) and an accelerated rate of disappearance of methyl red (Vmax = 0.3203 g/L/h) compared to the free cells. Furthermore, the gellan gum beads could be reused up to nine batches without substantial loss in the catalytic activity indicating the economic importance of this protocol. Analysis of methyl red degradation products revealed no germination inhibition on Triticum aestivum and Vigna radiata demonstrating complete toxicity removal of the parent dye after biological treatment. The occurrence of new and altered peaks (UV-Vis and FTIR) further supported the notion that the removal of methyl red by Rhodococcus strain UCC 0016 was indeed through biodegradation. Therefore, this strain has a huge potential as a candidate for efficient bioremediation of wastewater containing methyl red.
The capability of the crude extract of Rhodococcus UKMP-5M was enhanced by adopting the technology of immobilization. Among the matrices screened to encapsulate the crude extract, gellan gum emerged as the most suitable immobilization material, exceeding the activity of cyanide-degrading enzyme by 61% and 361% in comparison to alginate carrier and non-immobilized crude extract, respectively. Improved bead mechanical strength which supported higher biocatalyst activity by 63% was observed when concentration of gellan gum, concentration of calcium chloride, number of beads and bead size were optimized. The immobilized crude extract demonstrated higher tolerance towards broad range of pH (5-10) and temperature (30°C-40°C), superior cyanide-degrading activity over time and improved storage stability by maintaining 76% of its initial activity after 30 days at 4°C. Furthermore, repeated use of the gellan gum beads up to 20 batches without substantial loss in the catalytic activity was documented in the present study, indicating that the durability of the beads and the stability of the enzyme are both above adequate. Collectively, the findings reported here revealed that the utilization of the encapsulated crude extract of Rhodococcus UKMP-5M can be considered as a novel attempt to develop an environmentally favourable and financially viable method in cyanide biodegradation.
Natural growth-promoting nutrients extracted from aquaculture sludge waste can be used to maximise microalgal growth. This study identified the influence of aquaculture sludge extract (SE) on four microalgae species. Conway or Bold's Basal Media (BBM) was supplemented with SE collected from a Sabak Bernam shrimp pond (SB) and Kota Puteri fish pond (KP), and tested using a novel microplate-incubation technique. Five different autoclave extraction treatment parameters were assessed for both collected SE, i.e., 1-h at 105 °C, 2-h at 105 °C, 1-h at 121 °C, 2-h at 121 °C, and 24-h at room temperature (natural extraction). Microalgae culture in the microplates containing control (media) and enriched (media + SE) samples were incubated for nine days, at 25 °C with the light intensity of 33.75 μmol photons m-2 s-1 at 12-h light/dark cycle. The total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) in KP SE were 44.0-82.0 mg L-1 and 0.96-8.60 mg L-1. TDN (8.0%-515.0%) and TDP (105%-186 %) were relatively higher in KP SE compared to SB SE. The growth of microalgae species Nannochloropsis ocenica showed significant differences (p < 0.05) between the five extraction treatments from SB and the control. However, Chlorella vulgaris, Neochloris conjuncta, and Nephroclamys subsolitaria showed no significant differences (p > 0.05) in SB SE. N. ocenica, C. vulgaris, and N. conjuncta showed significant differences (p < 0.05) between five extraction treatments from KP and the control while N. subsolitaria showed no significant difference (p > 0.05). The specific growth rate (SGR) in the exponential phase of all microalgae species were relatively higher in SB SE compared to KP SE. While the organic matter content of KP SE was relatively higher, there were no significant differences in microalgae growth compared to SB SE. Nonetheless, modified SE did influence microalgae growth compared to the control. This study shows that modified SE could be used as enrichment media for microalgae cultivation.
Soil extracts are useful nutrients to enhance the growth of microalgae. Therefore, the present study attempts for the use of virgin soils from Peninsular Malaysia as growth enhancer. Soils collected from Raja Musa Forest Reserve (RMFR) and Ayer Hitam Forest Reserve (AHFR) were treated using different extraction methods. The total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and dissolved organic carbon (DOC) concentrations in the autoclave methods were relatively higher than natural extraction with up to 132.0 mg N/L, 10.7 mg P/L, and 2629 mg C/L, respectively for RMFR. The results of TDN, TDP, and DOC suggested that the best extraction methods are autoclaved at 121 °C twice with increasing 87%, 84%, and 95%, respectively. Chlorella vulgaris TRG 4C dominated the growth at 121 °C twice extraction method in the RMRF and AHRF samples, with increasing 54.3% and 14%, respectively. The specific growth rate (µ) of both microalgae were relatively higher, 0.23 d-1 in the Ayer Hitam Soil. This extract served well as a microalgal growth promoter, reducing the cost and the needs for synthetic medium. Mass production of microalgae as aquatic feed will be attempted eventually. The high recovery rate of nutrients has a huge potential to serve as a growth promoter for microalgae.
The assessment of water-extractable organic matter using an autoclave can provide useful information on physical, chemical, and biological changes within the soil. The present study used virgin forest soils from Chini Forest Reserve, Langkawi Island, and Kenyir Forest Reserve (Malaysia), extracted using different extraction methods. The dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and ammonium-nitrate content were higher in the autoclave treatments, up to 3.0, 1.3, 1.2, and 1.4 times more than by natural extraction (extracted for 24 h at room temperature). Overall, the highest extractable DOC, TDN, TDP, ammonium and nitrate could be seen under autoclaved conditions 121 °C 2×, up to 146.74 mg C/L, 8.97 mg N/L, 0.23 mg P/L, 5.43 mg N mg/L and 3.47 N mg/L, respectively. The soil extracts became slightly acidic with a higher temperature and longer duration. Similar trends were observed in the humic and nonhumic substances, where different types of soil extract treatments influenced the concentrations of the fractions. Different soil extraction methods can provide further details, thus widening the application of soil extracts, especially in microbes.