The effect of salinity, redox mediators and temperature on anaerobic biodegradation of petroleum hydrocarbons in microbial fuel cells.

Microbial fuel cells (MFCs) need to be robust if they are to be applied in the field for bioremediation. This study investigated the effect of temperature (20-50°C), salinity (0.5-2.5% (w/v) as sodium chloride), the use of redox mediators (riboflavin and anthraquinone-2-sulphonate, AQS) and prolonged fed-batch operation (60 days) on biodegradation of a petroleum hydrocarbon mix (i.e. phenanthrene and benzene) in MFCs. The performance criteria were degradation efficiency, % COD removal and electrochemical performance. Good electrochemical and degradation performance were maintained up to a salinity of 1.5% (w/v) but deteriorated by 35-fold and 4-fold respectively as salinity was raised to 2.5%w/v. Degradation rates and maximum power density were both improved by approximately 2-fold at 40°C compared to MFC performance at 30°C but decreased sharply by 4-fold when operating temperature was raised to 50°C. The optimum reactor performance obtained at 40°C was 1.15 mW/m(2) maximum power density, 89.1% COD removal and a degradation efficiency of 97.10%; at moderately saline (1% w/v) conditions the maximum power density was 1.06 mW/m(2), 79.1% COD removal and 91.6% degradation efficiency. This work suggests the possible application of MFC technology in the effective treatment of petroleum hydrocarbons contaminated site and refinery effluents.

Proteomics analysis of Bacillus licheniformis in response to oligosaccharides elicitors.

The role of oligosaccharides as biotic elicitors has been recognised in the enhanced production of antibiotics from fungal and bacterial cultures. The yield of bacitracin A in cultures of Bacillus licheniformis was increased after supplementation with oligoguluronate (OG), and mannan oligosaccharides (MO) and its mechanism at transcription level been established already. However, the elicitation mechanism at post transcriptional level has not been reported so far. In this paper we investigate changes in proteomics of B. licheniformis in presence of the oligosaccharide elicitors OG and MO. Differentially expressed proteins were examined using 2D-PAGE stained with colloidal Coomassie and were further identified by LC-MS/MS. We identified 19 differentially expressed proteins including those involved in carbon metabolism, energy generation, amino acid biosynthesis, oxidative and general stress response. The novel findings of this work, together with previous reports, contribute to the unravelling of the overall mechanism of elicitation in B. licheniformis cultures and reliability of the use of these elicitors for potential industrial application.

Impact of linoleic acid supplementation on lovastatin production in Aspergillus terreus cultures.

This work proposes a novel approach for enhancing the yield of lovastatin in Aspergillus terreus cultures by exploiting linoleic acid-derived signalling molecules, which are potentially involved in fungal cell-cell communication. High-performance liquid chromatography analysis revealed that production of lovastatin was enhanced up to 1.8-fold upon exogenous addition of the oxylipin precursor linoleic acid to low cell density cultures of A. terreus. Real-time PCR analysis showed that supplementation of linoleic acid also resulted in an increase in transcriptional levels of lovastatin biosynthetic genes lovB and lovF, indicating a transcriptional control of fatty acids (linoleic acid) on these genes in A. terreus. This study therefore demonstrates for the first time the potential of an oxylipin molecule as an enhancer of a fungal secondary metabolite production with positive impact for industrial exploitation.

Elicitation effects of oligosaccharides on the transcriptional level of bacitracin ABC transporter genes in Bacillus licheniformis.

Bacitracin ABC transporter comprises a self-resistance system in Bacillus licheniformis against its own product (bacitracin). Elicitation effects of carbohydrates on transcription level of bcrABC genes encoding bacitracin ABC transporter system were investigated through quantification by real-time PCR. Increases of 68% and 29% in bacitracin A yields after 36 h were achieved in cultures supplemented with oligoguluronate and oligoguluronate/mannan oligosaccharide combination. Cultures with combined elicitors showed 3, 2.6 and 3 transcriptional fold-changes in bcrA, bcrB and bcrC, respectively, compared to control. This could be due to a secondary effect caused by increased bacitracin A yield through elicitation.

Effect of oligosaccharide elicitors on bacitracin A production and evidence of transcriptional level control.

The role of oligosaccharides as biotic elicitors for the enhanced production of antibiotics and enzymes has been established in recent years. These findings could have significant promise for the pharmaceutical and biotechnology industries. Before the elicitors could be used at large-scale, reproducible production and high levels of enhancement are essential. In order to ensure the robustness of elicitation and exploit the process an understanding of this phenomenon at the molecular level is required. Bacitracin produced by Bacillus licheniformis is widely used as an animal feed additive and antibiotic against Gram-positive bacteria. In this work we report, the effect of single and multiple additions of different elicitors to B. licheniformis cultures for the production of bacitracin A. The results obtained showed that single addition of oligoguluronate to the cultures enhanced the levels of bacitracin A by 23.3%. Moreover, multiple elicitor addition of oligoguluronate and mannan oligosaccharide further enhanced the production of bacitracin A by 13.2% and 36.5% compared to single elicitor addition and control cultures, respectively. In addition, for the first time, it was found that elicitor supplementation of cultures increased the transcription level of the bacitracin biosynthetic genes bacABC, indicating transcriptional level control of the elicitor.