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Abstract This study aims to elucidate the mechanism of carbon partitioning towards starch and triacylglycerol (TAG) under nitrogen stress. Whole-transcriptome analysis was performed using RNA sequencing before being validated with qRT-PCR. The strain, Chlorella vulgaris UPSI-JRM01, exhibited a two-stage response to nitrogen stress: i) carbohydrate accumulation, plastid protein degradation and amino acid biosynthesis; and ii) lipid accumulation, carbohydrate degradation and DNA damage. In the first stage, the genes responsible for plastid protein degradation (CD4A), amino acid biosynthesis (arg, GLSN, AHCY, win1), carbon fixation (RuBisCO, GapC, fba, TK) and starch synthesis (SS, SBE2) were upregulated. In the second stage, the upregulation of genes responsible for starch degradation (SP), glycolysis (PFO, PK, ACS), fatty acid biosynthesis (FabH, accD) and TAG accumulation (DGAT2) were observed. By contrast, the components of photosystem I (PsbD, PsbC, PsbB), photosystem II (PsaA), cytochrome b6/f (PetA, PetG) and F-type ATPase (beta, alpha) were downregulated. The results suggested that nitrogen stress triggered high starch accumulation before the carbon was partitioned towards triacylglycerol (TAG) for long-term energy storage by two different pathways: chloroplastic TAG synthesis and glycerolipid metabolism. The starch build-up functions served as a rapid response to nitrogen stress, whereas subsequent lipid accumulation benefited the long-term storage of energy. This research provides in-depth understanding of the metabolic changes triggered by nitrogen stress.

Influence of different pretreated sludge for electricity generation in microbial fuel cells (MFCs) was investigated in this study. Pre-treatment has shown significant improvement in MFC electricity productivity especially from microwave treated sludge. Higher COD reduction in the MFC has been revealed from microwave treated sludge with 55% for total and 85% for soluble COD, respectively. Nonetheless, longer ozonation treatment did not give additional advantage compared to the raw sludge. On the other hand, samples from anodes were analyzed using the 16S rRNA gene-based pyrosequencing technique for microbial community analysis. There was substantial difference in community compositions among MFCs fed with different pretreated sludge. Bacteroidetes was the abundant bacterial phylum dominated in anodes of higher productivity MFCs. These results demonstrate that using waste sludge as the substrate in MFCs could achieve both sludge reduction and electricity generation, and proper pre-treatment of sludge could improve the overall process performance.

Pseudomonas aeruginosa RW9 is a promising candidate for the bioremediation of chromium hexavalent (Cr(VI)) pollution, as it resists a high concentration of up to 60 mg/L of Cr(VI). Leaving cells exposed to Cr(VI) has large bioreduction potential, implying its capacity to extract the ions from the contaminated medium. In this study, the tolerance for and distribution of Cr(VI) were investigated to identify the cells’ adaptation and removal strategies. Micro-characterization analysis was conducted to assess the effect of Cr(VI) on the cells. The cells’ elongation was observed at higher Cr(VI) concentrations, signifying their adaptation to DNA damage caused by Cr(VI) toxicity. Cr(VI) distribution analysis showed that the strain developed a complex mechanism to adapt to Cr(VI), based on surface-bound (0.46 mg/L), intracellularly accumulated (1.24 mg/L) and extracellular sequestration (6.74 mg/L), which accounted for 85% of the removal efficiency. The extracellular sequestration might be attributable to the production of metabolites, in accordance with the fourier-transform infrared spectroscopy (FTIR) spectra and orcinol analysis that confirmed the presence of a glycolipid biosurfactant, rhamnolipid. Remarkably, the rhamnolipid was slightly induced in the presence of Cr(VI). From the data obtained, it was confirmed that this local strain is well equipped to survive high doses of Cr(VI) and has great potential for application in Cr(VI) bioremediation.

Bioconverting glycerol into various valuable products is one of glycerol's promising applications due to its high availability at low cost and the existence of many glycerol-utilizing microorganisms. Bioethanol and biohydrogen, which are types of renewable fuels, are two examples of bioconverted products. The objectives of this study were to evaluate ethanol production from different media by local microorganism isolates and compare the ethanol fermentation profile of the selected strains to use of glucose or glycerol as sole carbon sources. The ethanol fermentations by six isolates were evaluated after a preliminary screening process. Strain named SS1 produced the highest ethanol yield of 1.0 mol: 1.0 mol glycerol and was identified as Escherichia coli SS1 Also, this isolated strain showed a higher affinity to glycerol than glucose for bioethanol production.