Optimization of culture conditions and properties of immobilized sulfide oxidase from Arthrobacter species

Sulfide removal characteristics, pathways and potential application of a novel chemolithotrophic sulfide-oxidizing strain, Marinobacter sp. SDSWS8

Sulfide generally exists in wastewater, black and odor river, as well as aquaculture water, and give rise to adverse effect on ecological stability and biological safety, due to the toxicity, corrosivity and malodor of sulfide. In the present study, a chemolithotrophic sulfide-oxidizing bacteria (SOB) was isolated and identified as Marinobacter maroccanus strain SDSWS8. And it produced no hemolysin and was susceptible to most antibiotics. There were no accumulation of sulfide, sulfate and thiosulfate during the sulfide removal process. The optimum conditions of sulfide removal were temperature 15-40 °C, initial pH value 4.5-9.5, salinity 10-40‰, C/N ratio 0-20 and sulfide concentration 25-150 mg/L. The key genes of sulfide oxidation, Sox system (soxB, soxX, soxA, soxZ, soxY, soxD, soxC), dissimilatory sulfur oxidation (dsrA, aprA and sat) and sqr, were successfully amplified and expressed, indicating the three pathways coordinated to complete the sulfide oxidation. Besides, strain SDSWS8 had inhibitory effect on four pathogen Vibrio (V. harveyi, V. parahaemolyticus, V. anguillarum and V. splendidus). Furthermore, efficient removal of sulfide from real aquaculture water and sludge mixture could be accomplished by strain SDSWS8. This study may provide a promising candidate strain for sulfide-rich water treatment.

Heterotrophic sulfide-oxidizing nitrate-reducing bacteria enables the high performance of integrated autotrophic-heterotrophic denitrification (IAHD) process under high sulfide loading

Micro-aerobic enhancement technology has been developed as an effective tool to enhance simultaneous removal of sulfide, nitrate and organic carbon during the integrated autotrophic-heterotrophic denitrification (IAHD) process under high loading; however, its mechanism of enhancement for functional bacteria remains ambiguous. In this study, we discovered that heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-soNRB) are responsible for enhancing IAHD performance under micro-aerobic conditions with high sulfide loading. In a continuous IAHD bioreactor, aeration rate of 2.6 mL min^-1·L^-1 promoted 2 to 4 times higher removal efficiencies of sulfide, nitrate and acetate with an influent sulfide concentration of 18.75 mmol/L. Metagenomic analysis revealed that trace oxygen stimulated the abundance of genes responsible for sulfide oxidation (sqr, glpE, pdo, sox and cysK), which were upregulated by 15.2%-129.9%, and the genes encoding nitrate reductase were up-regulated by 67.4%. The increased acetate removal efficiency was attributed to upregulation of ack, pta and TCA cycle related genes. The h-NRB Pseudomonas, Azoarcus, Thauera and Halomonas were detected and regarded as h-soNRB in our bioreactor. According to Illumina MiSeq sequencing, these genera were absolutely dominant in the micro-aerobic microbial community at relative abundances ranging from 82.72% to 90.84%. The sulfide, nitrate and acetate removal rates of Pseudomonas C27, a typical h-soNRB, were at least 10 times higher under micro-aerobic conditions than under anaerobic conditions. Besides, the sulfur, nitrogen and carbon metabolic network was constructed based on the Pseudomonas C27 genome. The pdo and cysK genes found in this strain may be the most advantageous for autotrophic sulfide oxidizing nitrate reducing bacteria (a-soNRB), which are closely related to the high-efficiency sulfide, nitrate and acetate removal performance under high sulfide concentrations and a limited oxygen supply. In addition, after micro-aerobic cultivation, the anaerobic sulfide loading tolerance of the IAHD bioreactor increased from 18.75 to 37.5 mmol/L with sulfide, nitrate and acetate removal efficiencies increasing 1.5 to 3 times, which suggests that intermittent micro-aeration might be a more economical and efficient regime for high-sulfide IAHD regulation.

Seasonal characteristics of odor and methane mitigation and the bacterial community dynamics in an on-site biocover at a sanitary landfill

Landfills are key anthropogenic emission sources for odors and methane. For simultaneous mitigation of odors and methane emitted from landfills, a pilot-scale biocover (soil:perlite:earthworm cast:compost, 6:2:1:1, v/v) was constructed at a sanitary landfill in South Korea, and the biocover performance and its bacterial community dynamics were monitored for 240 days. The removal efficiencies of odor and methane were evaluated to compare the odor dilution ratios or methane concentrations at the biocover surface and landfill soil cover surface where the biocover was not installed. The odor removal efficiency was maintained above 85% in all seasons. The odor dilution ratios ranged from 300 to 3000 at the biocover surface, but they were 6694-20,801 at the landfill soil cover surface. Additionally, the methane removal efficiency was influenced by the ambient temperature; the methane removal efficiency in winter was 35-43%, while the methane removability was enhanced to 85%, 86%, and 96% in spring, early summer, and late summer, respectively. The ratio of methanotrophs to total bacterial community increased with increasing ambient temperature from 5.4% (in winter) to 12.8-14.8% (in summer). In winter, non-methanotrophs, such as Acinetobacter (8.8%), Rhodanobacter (7.5%), Pedobacter (7.5%), and Arthrobacter (5.7%), were abundant. However, in late summer, Methylobacter (8.8%), Methylocaldum (3.4%), Mycobacterium (1.1%), and Desulviicoccus (0.9%) were the dominant bacteria. Methylobacter was the dominant methanotroph in all seasons. These seasonal characteristics of the on-site biocover performance and its bacterial community are useful for designing a full-scale biocover for the simultaneous mitigation of odors and methane at landfills.

Autotrophic and heterotrophic denitrification by a newly isolated strain Pseudomonas sp. C27

The denitrifying sulfide removal (DSR) process applied autotrophic and heterotrophic denitrification pathways to achieve simultaneous conversion of nitrate to N2, sulfide to elementary sulfur, and organic substances to CO2. The current bottlenecks impeding the development of DSR process include the need of balanced growth of both autotrophic denitrifiers and heterotrophic denitrifers in the same reactor and the capability of treating wastewaters at fix compositions. This work isolated a strain, identified as Pseudomonas sp. C27 (GenBank accession number GQ241351), which can grow on heterotrophic and mixotrophic media and can perform both autotrophic and heterotrophic denitrification in mixotrophic medium. The C27 strain can grow well on succinate, acetate, malate, priopionate and ethanol and has the optimal growth temperature at 25-30°C and pH at 9.0. Pathways of DSR reactions by C27 were proposed. Discussion on the potential use of the isolated C27 in novel DSR process was available.

Inhibitory effects of a branched-chain fatty acid on larval settlement of the polychaete Hydroides elegans

Eleven strains of Streptomyces isolated from deep-sea sediments were screened for anti-larval settlement activity and all were active. Among those strains, Streptomyces sp. UST040711-290 was chosen for the isolation of bioactive antifouling compounds through bioassay-guided isolation procedure. A branched-chain fatty acid, 12-methyltetradecanoid acid (12-MTA) was purified, and it strongly inhibited the larval settlement of the polychaete Hydroides elegans. Streptomyces sp. UST040711-290 produced the highest yield of 12-MTA when the bacterium was cultured at 30 degrees C and pH 7.0 in a modified MGY medium. To investigate the potential antifouling mechanism of 12-MTA in the larval settlement of Hydroides elegans, the expression level of four marker genes, namely, Ran GTPase activating protein (GAP), ATP synthase (AS), NADH dehydrogenase (ND), and cell division cycle protein (CDC), was compared among the untreated larvae (the control), isobutylmethylxanthine (an effective settlement inducer), and 12-MTA-treated larvae. The 12-MTA treatment down-regulated the expression of GAP and up-regulated the expression of AS in the H. elegans larvae, but did not affect the expression of ND and CDC. This study provides the first evidence that a branched-chain fatty acid produced by a marine bacterium isolated from deep-sea sediment effectively inhibited the larval settlement of the biofouling polychaete H. elegans and its effects on the expression of genes important for larval settlement.