Protective effects of farnesol on a Rhizobium strain exposed to cadmium

Recovery and utilization of waste filtrate from industrial biological fermentation: Development and metabolite profile of the Bacillus cereus liquid bio-fertilizer

Most fermentation waste filtrates can be used as raw materials for producing bio-fertilizers to reduce wastewater emissions and environmental pollution, but their bio-fertilizer utilization depends on the nutrients contained and their metabolized by functional microorganism. To achieve bio-fertilizer utilization of Acremonium terricola fermented waste filtrate, this study systematically explored the functional microbial species for making good use of waste liquid, optimized material process parameters for bio-fertilizer production based on D-optimal mixture design method, and analyzed the composition of the waste filtrate and its metabolism by functional microorganisms using a non-targeted LC-MS metagenomics technique. The results showed that Bacillus cereus was the functional microbial candidate for producing bio-fertilizer because of its more efficiently utilize the waste filtrate than other Bacillus sp. The optimal material process parameters of the liquid bio-fertilizer were the inoculum dose of 5% (v:v, %), 80% of waste filtrate, 0.25% of N, 3.5% of P2O5, 3.25% of K2O of mass percentage. Under these conditions, the colony forming unit (CFU) of Bacillus cereus could reach (1.59 ± 0.01) × 108 CFU/mL, which met the bio-fertilizer standard requirements of the People's Republic of China (NY/T798). Furthermore, the potential functions of bio-fertilizer were studied based on comparison of raw materials and production components: on the one hand, waste filtrate contained abundant of nitrogen and carbon sources, and bioactive substances secreted by Acremonium terricola, such as β-alanyl-L-lysine, anserine, UMP, L-lactic acid and etc., which could meet the nutrient requirements of the growth of Bacillus cereus; On the other hand, some compounds of waste filtrate with the potential to benefit the plant growth and defense, such as betaine aldehyde, (2E,6E)-farnesol, homogentisic acid and etc., were significantly up regulated by Bacillus cereus utilization of the filtrate. To sum up, this work highlighted that the waste filtrate could be efficiently developed into liquid bio-fertilizer by Bacillus cereus.

Effects of volatile sulfur compounds on growth and oxidative stress of Rhizobium leguminosarum E20-8 exposed to cadmium

Volatile sulfur compounds (VSCs) have been reported to be produced by many bacterial species. Depending on the compound, they can negatively influence some organisms (fungi, nematodes and insects) or promote plant growth. Some of these compounds have also been hypothesized to play a role in bacterial response to cadmium (Cd) induced stress. This study aimed to assess the potential effects of four VSCs (dimethyl sulfide - DMS, dimethyl disulfide - DMDS, dimethyl trisulfide - DMTS and methyl thioacetate - MTA) on the growth and oxidative status of Rhizobium sp. strain E20-8 via airborne exposure, in order to test the hypothesis that these volatile compounds can influence growth and tolerance to cadmium. Our results show that, overall, the tested compounds triggered similar antioxidant mechanisms in Rhizobium in the presence of Cd. The protective effect at the membrane level by DMDS and DMTS particularly demonstrates the antioxidant effect of these volatiles, with reductions of up to 50% (DMS) and 80% (DMTS) in lipid peroxidation levels. Due to the volatile nature of these compounds, the low concentrations tested (1 nM to 100 mM), and considering that they are released by bacteria and other organisms such as plants, it is possible that these effects also occur in the soil ecosystem.

Analysis of biosorption and biotransformation mechanism of Pseudomonas chengduensis strain MBR under Cd(II) stress from genomic perspective

Microbial treatment of heavy metal-polluted sites is considered an environmentally friendly bioremediation technology with high potential. This study shows that Pseudomonas chengduensis strain MBR, a bacterium that can potentially be applied in the treatment of heavy metal pollution, is most affected by Cd(II) stress at the beginning of its growth. Up to 100% of total Cd(II) adsorption occurs in the first 48 h after treatment of stationary phase cells with Cd(II). A biofilm forms on the cell surface, Cd(II) adsorbs, and is reduced to Cd (0) in the form of nanoscale particles. The genome of strain MBR was sequenced, annotated and analyzed. We identified various genes potentially related to cadmium resistance, transport and metabolism. Analysis of the strain MBR genome is helpful to explore the mechanism of Cd(II) resistance, and can provide new ideas for cadmium pollution control.

Rhizobium response to sole and combined exposure to cadmium and the phytocompounds alpha-pinene and quercetin

Soils can be contaminated with substances arising from anthropogenic sources, but also with natural bioactive compounds produced by plants, such as terpenes and flavonoids. While terpenes and flavonoids have received much less attention from research studies than metals, the effects that phytocompounds can have on soil organisms such as beneficial microorganisms should not be neglected. Herein we report the sole and combined exposure of Rhizobium to cadmium, to the monoterpene alpha-pinene and to the flavanol quercetin. A range of environmentally relevant concentrations of the phytocompounds was tested. Physiological (growth, protein content and intracellular Cd concentration), oxidative damage (lipid peroxidation, protein carbonylation) and antioxidant mechanisms (superoxide dismutase, catalase, glutathione, glutathione-S-transferases, protein electrophoretic profiles) were assessed. Results suggest that exposure to both phytocompounds do not influence Rhizobium growth, but for combined exposure to phytocompounds and Cd, different responses are observed. At low concentrations, phytocompounds seem to relieve the stress imposed by Cd by increasing antioxidant responses, but at high concentrations this advantage is lost and membrane damage may even be exacerbated. Thus, the presence of bioactive phytocompounds in soil may influence the tolerance of microorganisms to persistent toxicants, and may change their impact on the environment.

Airborne exposure of Rhizobium leguminosarum strain E20-8 to volatile monoterpenes: Effects on cells challenged by cadmium

Volatile organic compounds (VOCs) are produced by plants, fungi, bacteria and animals. These compounds are metabolites originated mainly in catabolic reactions and can be involved in biological processes. In this study, the airborne effects of five monoterpenes (α-pinene, limonene, eucalyptol, linalool, and menthol) on the growth and oxidative status of the rhizobial strain Rhizobium leguminosarum E20-8 were studied, testing the hypothesis that these VOCs could influence Rhizobium growth and tolerance to cadmium. The tested monoterpenes were reported to have diverse effects, such as antibacterial activity (linalool, limonene, α-pinene, eucalyptol), modulation of antioxidant response or antioxidant properties (α-pinene and menthol). Our results showed that non-stressed cells of Rhizobium E20-8 have different responses (growth, cell damage and biochemistry) to monoterpenes, with α-pinene and eucalyptol increasing colonies growth. In stressed cells the majority of monoterpenes failed to minimize the detrimental effects of Cd and increased damage, decreased growth and altered cell biochemistry were observed. However, limonene (1 and 100 mM) and eucalyptol (100 nM) were able to increase the growth of Cd-stressed cells. Our study evidences the influence at-a-distance that organisms able to produce monoterpenes may have on the growth and tolerance of bacterial cells challenged by different environmental conditions.

The role of volatiles in Rhizobium tolerance to cadmium: Effects of aldehydes and alcohols on growth and biochemical endpoints

Rhizobia have a significant agronomic and environmental role and are eminent contributors to soil fertility. However, this group of microorganisms are affected by various environmental stresses, such as Cd contamination. High Cd concentrations change bacterial metabolism. During this metabolic shift, bacteria alter their volatilome (the set of volatile metabolites synthesized by an organism). In the presence of Cd, peak areas of saturated aldehydes and alcohols were previously reported to increase, and the consequences of this increase to cells are poorly known. In this study, Rhizobium sp. strain E20-8 cells were exposed to Cd and aldehydes or their conjugated alcohols. Exposure to Cd (100 μM) inhibited cell growth and induced several biomarkers of oxidative stress. The present study also evidenced the higher toxicity of most aldehydes relatively to the corresponding alcohol in the presence of Cd, suggesting that reduction of aldehydes into alcohols may be an effective mechanism to restrain aldehydes toxicity in Rhizobium cells under Cd toxicity. Nonetheless, the protective effect was dependent on the pair aldehyde-respective alcohol considered and it differed between Cd stressed and non-stressed cells. Differences in the ability to convert aldehydes to alcohols may emerge as a new feature helping explain the oxidative tolerance variability among bacteria.

Fungal Quorum-Sensing Molecules and Inhibitors with Potential Antifungal Activity: A Review

The theory of persisting independent and isolated regarding microorganisms is no longer accepted. To survive and reproduce they have developed several communication platforms within the cells which facilitates them to adapt the surrounding environmental changes. This cell-to-cell communication is termed as quorum sensing; it relies upon the cell density and can stimulate several traits of microbes including biofilm formation, competence, and virulence factors secretion. Initially, this sophisticated mode of communication was discovered in bacteria; later, it was also confirmed in eukaryotes (fungi). As a consequence, many quorum-sensing molecules and inhibitors have been identified and characterized in various fungal species. In this review article, we will primarily focus on fungal quorum-sensing molecules and the production of inhibitors from fungal species with potential applications for combating fungal infections.