Ultrastructural and Intracellular Chemical Changes of a Novel Halophilic Strain V430 of Staphylococcus saprophyticus under CaCl2 Stress

Effects of nitrogen supply on hydrogen-oxidizing bacterial enrichment to produce microbial protein: Comparing nitrogen fixation and ammonium assimilation

To investigate the effects of nitrogen source supply on microbial protein (MP) production by hydrogen-oxidizing bacteria (HOB) under continuous feed gas provision, a sequencing batch culture comparison (N2 fixation versus ammonium assimilation) was performed. The results confirmed that even under basic cultivation conditions, N2-fixing HOB (NF-HOB) communities showed higher levels of CO2 and N2 fixation (190.45 mg/L Δ CODt and 11.75 mg/L Δ TNbiomass) than previously known, with the highest biomass yield being 0.153 g CDW/g COD-H2. Rich ammonium stimulated MP synthesis and the biomass accumulation of communities (increased by 7.4 ～ 14.3 times), presumably through the enhancement of H2 and CO2 absorption. The micro mechanism may involve encouraging the enrichment of species like Xanthobacter and Acinetobacter then raising the abundance of nitrogenase and glutamate synthase to facilitate the nitrogen assimilation. This would provide NF-HOB with ideas for optimizing their MP synthesis activity.

Mechanism on the microbial salt tolerance enhancement by electrical stimulation

The application of biological methods in industrial saline wastewater treatment is limited, since the activities of microorganisms are strongly inhibited by the highly concentrated salts. Acclimatized halotolerant and halophilic microorganisms are of high importance since they can resist the environmental stresses of high salinity. The acclimation to salinity can be passive or active based on whether external simulation is used. However, there is a need for development of economic, efficient and reliable active biological stimulation technologies to accelerate salinity acclimation. Recent studies have shown that electrical stimulation can effectively enhance microbial salt tolerance and pollutant removal ability. However, there have been no comprehensive reviews of the mechanisms involved. Therefore, this mini-review described the mechanisms of electrical stimulation that can significantly improve microbial bioactivity and biodiversity. These mechanisms include regulation of Na⁺ and K⁺ transporters by changing membranepotential and promoting ATP production, as well as regulation of extracellular polymer substances through enhanced release of low molecular weight EPS and quorum sensing molecules. The information provided herein will facilitate the application of biological high-salinity wastewater treatment.

Calcium Carbonate Addition Improves L-Methionine Biosynthesis by Metabolically Engineered Escherichia coli W3110-BL

L-Methionine (L-Met) is a sulfur-containing amino acid, which is one of the eight essential amino acids to human body. In this work, the fermentative production of L-Met with genetically engineered Escherichia coli W3110-BL in a 5-L fermentor was enhanced through supplement of Ca²⁺ into the fermentation medium. With the addition of 30 g/L calcium carbonate (CaCO₃), the titer of L-Met and yield against glucose reached 1.48 g/L and 0.09 mol/mol glucose, 57.45% higher than those of the control, respectively. The flux balance analysis (FBA) revealed that addition of CaCO₃ strengthened the tricarboxylic acid cycle and increased the intracellular ATP concentration by 39.28%. The re-distribution of carbon, ATP, and cofactors flux may collaborate to improve L-Met biosynthesis with E. coli W3110-BL. The regulation of citrate synthase and oxidative phosphorylation pathway was proposed to be important for overproduction of L-Met. These foundations provide helpful reference in the following metabolic modification or fermentation control for further improvement of L-Met biosynthesis.

Electrical stimulation improves microbial salinity resistance and organofluorine removal in bioelectrochemical systems

Fed batch bioelectrochemical systems (BESs) based on electrical stimulation were used to treat p-fluoronitrobenzene (p-FNB) wastewater at high salinities. At a NaCl concentration of 40 g/liter, p-FNB was removed 100% in 96 h in the BES, whereas in the biotic control (BC) (absence of current), p-FNB removal was only 10%. By increasing NaCl concentrations from 0 g/liter to 40 g/liter, defluorination efficiency decreased around 40% in the BES, and in the BC it was completely ceased. p-FNB was mineralized by 30% in the BES and hardly in the BC. Microorganisms were able to store 3.8 and 0.7 times more K(+) and Na(+) intracellularly in the BES than in the BC. Following the same trend, the ratio of protein to soluble polysaccharide increased from 3.1 to 7.8 as the NaCl increased from 0 to 40 g/liter. Both trends raise speculation that an electrical stimulation drives microbial preference toward K(+) and protein accumulation to tolerate salinity. These findings are in accordance with an enrichment of halophilic organisms in the BES. Halobacterium dominated in the BES by 56.8% at a NaCl concentration of 40 g/liter, while its abundance was found as low as 17.5% in the BC. These findings propose a new method of electrical stimulation to improve microbial salinity resistance.

Isolation and identification of dibutyl phthalate-degrading bacteria from hydrospheres in Tokyo

Dibutyl phthalate (DBP) is used widely as a plasticizer and is thought to negatively affect various organisms. To isolate and investigate DBP-degrading bacteria from hydrospheres in Tokyo, strains were selected on YNB medium containing DBP as the sole carbon source, and candidate strains were identified by zones of clearing around the colonies. Degradation of DBP by the strains was subsequently measured with HPLC, and bacterial identification was accomplished using 16S rDNA sequences. Nineteen strains of DBP degraders were isolated from activated sludge in a sewage treatment plant, from Tokyo Bay, and from the Takahama Canal. These strains degraded 16.8%-88.0% of DBP (0.1%, v/v) for 2 weeks and were identified as several species of Acinetobacter, as well as Tsukamurella tyrosinosolvens, Ochrobactrum anthropi, and Staphylococcus saprophyticus. Commercially available strains of Acinetobacter were also found to degrade DBP.