Demonstration of sequential adaptation strategy for developing salt tolerance in bacteria for wastewater treatment: a study using Escherichia coli as model

An efficient co-culture of Halomonas mongoliensis and Dunaliella salina for phenol degradation under high salt conditions

Phenol is one of the major organic pollutants in high salt industrial wastewater. The biological treatment method is considered to be a cost-effective and eco-friendly method, in which the co-culture of microalgae and bacteria shows a number of advantages. In the previous study, a co-culture system featuring Dunaliella salina (D. salina) and Halomonas mongoliensis (H. mongoliensis) was established and could degrade 400 mg L-1 phenol at 3% NaCl concentration. In order to enhance the performance of this system, D. salina strain was subjected to adaptive laboratory evolution (ALE) by gradually increasing the phenol concentration from 200 mg L-1 to 500 mg L-1 at 3% NaCl concentration. At a phenol concentration of 500 mg L-1, the phenol removal rate of the resulting D. salina was 78.4% within 7 days, while that of the original strain was only 49.2%. The SOD, POD, and MDA contents of the resulting strain were lower than those of the original strain, indicating that the high concentration of phenol was less harmful to the resulting strain. A co-culture system was established with the resulting D. salina and H. mongoliensis, which could complete degrade 500 mg L-1 of phenol within 8 days, outperforming the original D. salina co-culture system. This study proved that ALE could improve the phenol tolerance and phenol degradation capability of D. salina, and then effectively improve the phenol degradation capability of D. salina and H. mongoliensis co-culture system.

Mapping Microbial Capacities for Bioremediation: Genes to Genomics

Bioremediation is a process wherein the decontamination strategies are designed so that a site could achieve the environmental abiotic and biotic parameters close to its baseline. In the process, the driving force is the available microbial genetic degradative capabilities, which are supported by required nutrients so that the desired expression of these capabilities could be exploited in favour of removal of pollutants. With genomics tools not only the available abilities could be estimated but their dynamic performance could also be established. These tools are now playing important role in bioprocess optimization, which not only derive the bio-stimulation plans but also could suggest possible genetic bio-augmentation options.

The effect of adaptation of Lactobacillus amylovorus to increasing concentrations of sweet potato starch on the production of lactic acid for its potential use in the treatment of cannery waste

Lactobacillus amylovorus, an amylolytic species, was cultured in increasing concentrations of sweet potato starch to test the effect of this progressive acclimation on lactic acid production. This research is part of a project on the use of the waste stream from a sweet potato cannery to produce lactic acid. The media used for this acclimation was a modified version of the de Man, Rogosa and Sharpe medium, in which glucose was partially or totally substituted with sweet potato starch. The process was done in five steps, starting with 100% glucose in the first step and ending with 100% sweet potato starch in the last one. At each step, the effectiveness of the acclimation was tested by running fermentations with and without pH control for 62 h. The effect of the overall adaptation process was tested by comparing the growth and activity of the acclimated vs non-acclimated bacteria using sweet potato starch as the only source of carbohydrates. Growth and activity assessments indicated that L. amylovorus was able to ferment sweet potato starch into lactic acid. In most cases, pH control resulted in better substrate utilisation and larger amounts of lactic acid. In the comparison study, however, the adaptation process had a major influence on lactic acid production than the effect of pH. For 20 g L^-1 sweet potato starch media, adapted L. amylovorus under no pH control yielded 11.20 g L^-1 versus the non-adapted bacteria, which yielded 7.10 g L^-1. Under controlled pH conditions, 14.80 and 4.20 g L^-1 lactic acid were produced by adapted and non-adapted bacteria respectively.

Exploring stress tolerance mechanism of evolved freshwater strain Chlorella sp. S30 under 30 g/L salt

Enhancement of stress tolerance to high concentration of salt and CO₂ is beneficial for CO₂ capture by microalgae. Adaptive evolution was performed for improving the tolerance of a freshwater strain, Chlorella sp. AE10, to 30 g/L salt. A resulting strain denoted as Chlorella sp. S30 was obtained after 46 cycles (138 days). The stress tolerance mechanism was analyzed by comparative transcriptomic analysis. Although the evolved strain could tolerate 30 g/L salt, high salinity caused loss to photosynthesis, oxidative phosphorylation, fatty acid biosynthesis and tyrosine metabolism. The related genes of antioxidant enzymes, CO₂ fixation, amino acid biosynthesis, central carbon metabolism and ABC transporter proteins were up-regulated. Besides the up-regulation of several genes in Calvin-Benson cycle, they were also identified in C4 photosynthetic pathway and crassulacean acid metabolism pathway. They were essential for the survival and CO₂ fixation of Chlorella sp. S30 under 30 g/L salt and 10% CO₂.

A model on the biological treatment of saline wastewater

Water scarcity is not a new issue, neither is water pollution. While 70% of the earth’s surface is covered with water, only 3% of it is available as fresh water. Moreover the pollution of water resources has dramatically increased the problem of water scarcity over the last century. Bioremediation presents a cheap and effective solution of this problem. In particular, halophiles have been found to be effective in hypersaline wastewater treatment. Therefore, in this paper, we propose a nonlinear mathematical model to study the removal of a pollutant using halophiles in the hypersaline environment. The analysis of the model is being carried out using stability theory of differential equations. The results indicate that halophiles not only help in removing the organic pollutant, but also help in conversion of saline water into fresh water. The numerical simulations along with sensitivity analysis are performed to support the analytical results.

Dynamic interactive events in gene regulation using E. coli dehydrogenase as a model

Different approaches in gene expression analysis always provide a snapshot view of cellular events. During the bacterial growth, the decisions are dynamically made with participation of various genes and their interactions with modulating factors. We have selected Escherichia coli dehydrogenases as a model to capture these interactions. We have treated the cells with hydrogen peroxide with very low level and asked the questions how cellular physiology has modulated itself to survive post-shock conditions. We hypothesized that while global regulators and associated gene network dictate the overall cellular intelligence, specific redox-sensitive classes of enzymes like dehydrogenase-mediated modulation could provide the option to cell for survival under peroxide after-effect. To understand the dynamic gene interaction, we used multidimensional scaling of genes and overlaid with minimum spanning tree to understand the clustering patterns under different conditions. Study shows that under peroxide after-effect, it is the interplay of ArcA (global regulator), with ldhA (involved in intermediary metabolism) and ndh (managing co-factor NADH), that emerges as modulating association. Knockout mutants of global regulators confirmed the promoter activity trend through gene expression change for dehydrogenases.

An orphan two-component response regulator Slr1588 involves salt tolerance by directly regulating synthesis of compatible solutes in photosynthetic Synechocystis sp. PCC 6803

We report here the characterization of a novel orphan response regulator Slr1588 directly involved in the synthesis and transport of compatible solutes against salt stress.