Respiration suppress and apoptosis-like cell death of Escherichia coli in direct current therapy mediated by polypyrrole conductive hydrogel.

Targeting oxidative phosphorylation of bacteria is a novel antibiotic strategy leading to rapid cell death as a result of respiration suppress. Herein, a conductive polymer termed polypyrrole (PPy) is used to short-circuit the electron transfer chain (ETC) of bacteria cells owing to its higher electron affinity to electrons than all of the electron carriers on ETC. A hydrogel is fabricated using PPy which is anticipated to seize electrons from ETC and inhibit respiration of bacteria cells. The results show that the prepared PPy hydrogel can mediate an effective direct current (DC) antibacterial therapy which greatly enhances intracellular reactive oxygen species (ROS) level of Escherichia coli (E. coli), suppresses respiration, induces apoptosis-like cell death of E. coli accompanied by chromosomal condensation and loss of structural integrity, and rapidly cleared E. coli infection in vivo. Taken into the photothermal property of PPy, a combined direct current-photothermal therapy is developed which can enhance bacteria-killing effects with the assistance of an 808 nm laser. Our findings provide a new antibiotic strategy with metabolic pathway as a target.

Multi-Scenario Analysis of Habitat Quality in the Yellow River Delta by Coupling FLUS with InVEST Model.

The past decades were witnessing unprecedented habitat degradation across the globe. It thus is of great significance to investigate the impacts of land use change on habitat quality in the context of rapid urbanization, particularly in developing countries. However, rare studies were conducted to predict the spatiotemporal distribution of habitat quality under multiple future land use scenarios. In this paper, we established a framework by coupling the future land use simulation (FLUS) model with the Intergrated Valuation of Environmental Services and Tradeoffs (InVEST) model. We then analyzed the habitat quality change in Dongying City in 2030 under four scenarios: business as usual (BAU), fast cultivated land expansion scenario (FCLE), ecological security scenario (ES) and sustainable development scenario (SD). We found that the land use change in Dongying City, driven by urbanization and agricultural reclamation, was mainly characterized by the transfer of cultivated land, construction land and unused land; the area of unused land was significantly reduced. While the habitat quality in Dongying City showed a degradative trend from 2009 to 2017, it will be improved from 2017 to 2030 under four scenarios. The high-quality habitat will be mainly distributed in the Yellow River Estuary and coastal areas, and the areas with low-quality habitat will be concentrated in the central and southern regions. Multi-scenario analysis shows that the SD will have the highest habitat quality, while the BAU scenario will have the lowest. It is interesting that the ES scenario fails to have the highest capacity to protect habitat quality, which may be related to the excessive saline alkali land. Appropriate reclamation of the unused land is conducive to cultivated land protection and food security, but also improving the habitat quality and giving play to the versatility and multidimensional value of the agricultural landscape. This shows that the SD of comprehensive coordination of urban development, agricultural development and ecological protection is an effective way to maintain the habitat quality and biodiversity.

Identification of Specific Variations in a Non-Motile Strain of Cyanobacterium Synechocystis sp. PCC 6803 Originated from ATCC 27184 by Whole Genome Resequencing.

Cyanobacterium Synechocystis sp. PCC 6803 is a widely used model organism in basic research and biofuel biotechnology application. Here, we report the genomic sequence of chromosome and seven plasmids of a glucose-tolerant, non-motile strain originated from ATCC 27184, GT-G, in use at Guangzhou. Through high-throughput genome re-sequencing and verification by Sanger sequencing, eight novel variants were identified in its chromosome and plasmids. The eight novel variants, especially the five non-silent mutations might have interesting effects on the phenotype of GT-G strains, for example the truncated Sll1895 and Slr0322 protein. These resequencing data provide background information for further research and application based on the GT-G strain and also provide evidence to study the evolution and divergence of Synechocystis 6803 globally.

Sll0528, a Site-2-Protease, Is Critically Involved in Cold, Salt and Hyperosmotic Stress Acclimation of Cyanobacterium Synechocystis sp. PCC 6803.

Site-2-proteases (S2Ps) mediated proteolysis of transmembrane transcriptional regulators is a conserved mechanism to regulate transmembrane signaling. The universal presence of S2P homologs in different cyanobacterial genomes suggest conserved and fundamental functions, though limited data has been available. Here we provide the first evidence that Sll0528, a site-2-protease in Synechocystis sp. PCC 6803 is crucial for salt, cold and hyperosmotic stress acclimation. Remarkable induction of sll0528 gene expression was observed under salt, cold and hyperosmotic stress, much higher than induction of the other three S2Ps. Knock-out of sll0528 gene in wild type Synechocystis sp. PCC 6803 increased their sensitivity to salt, cold and hyperosmotic stress, as revealed by retarded growth, reduced pigments and disrupted photosystems. The sll0528 gene was induced to a much smaller extent by high light and mixotrophic growth with glucose. Similar growth responses of the sll0528 knockout mutant and wild type under high light and mixotrophic growth indicated that sll0528 was dispensable for these conditions. Recombinant Sll0528 protein could cleave beta-casein into smaller fragments. These results together suggest that the Sll0528 metalloprotease plays a role in the stress response and lays the foundation for further investigation of its mechanism, as well as providing hints for the functional analysis of other S2Ps in cyanobacteria.

Potential of chitinolytic Serratia marcescens strain JPP1 for biological control of Aspergillus parasiticus and aflatoxin.

Serratia marcescens strain JPP1 was isolated from peanut hulls in Huai'an city, Jiangsu Province, China. Its potential to inhibit the mycelial growth of Aspergillus parasiticus and the subsequent aflatoxin production was evaluated. The strain JPP1 could produce chitinase to degrade fungal cell walls, which was the main mechanism of strain JPP1 for biocontrol. Scanning electron microscopy of fungi treated with the crude chitinase revealed abnormal morphological changes. While the strain was grown in the peanut hulls-based medium, the chitinase activity reached 7.39 units. RT-PCR analysis showed that the crude chitinase repressed the transcription of genes involved in the aflatoxin gene cluster, such as aflR, aflC (pksL1), and aflO (dmtA) genes. By visual agar plate assay and tip culture method, the strain JPP1 exhibited remarkable inhibitory effect on mycelia growth (antifungal ratio >95%) and subsequent aflatoxin production (antiaflatoxigenic ratio >98%). An in vitro assay with seed coating agent of bacterial suspension showed that strain JPP1 effectively reduced fungal growth and subsequent aflatoxin production on peanut seeds, and its antagonistic effect was superior to the common agricultural fungicide of carbendazim. These characteristics suggest that S. marcescens JPP1 strain could potentially be utilized for the biological control of phytopathogenic fungi and aflatoxin in Chinese peanut main producing areas.

Diversity of culturable root-associated/endophytic bacteria and their chitinolytic and aflatoxin inhibition activity of peanut plant in China.

A total of 72 isolates of root-associated/endophytic (RAE) bacteria were isolated from peanut plants grown in the main producing areas of 6 provinces in China. The 16S rRNA gene sequences of these isolates were determined and phylogenetic analyses revealed that 72 isolates belonged to the classes Bacilli (49 isolates) and Gammaproteobacteria (23 isolates). The majority of RAE bacteria in Bacilli belonged to 2 genera, Bacillus and Lysinibacillus (48 and 1) while those in Gammaproteobacteria belonged to the genera Enterobacter, Serratia, Stenotrophomonas, and Pseudomonas (7, 11, 3 and 2 isolates, respectively). This is the first report of Lysinibacillus xylanilyticus isolate as biocontrol agent against AFs. All of the selected RAE bacteria showed inhibitory activities against Aspergillus parasiticus (A. parasiticus) growth and/or aflatoxins (AFs) production by visual agar plate assay and tip culture method. Most of the RAE bacteria strains (96 % strains) were determined to have decreased mycelia growth or AFs production levels by >50 % (p < 0.05). Bacterial isolates were further characterized for chitinolytic activity and 22 strains (30 % strains) of identified RAE bacteria degraded colloidal chitin on the chitin medium plate. Ten selected chitinolytic RAE bacteria were tested for antifungal activity on peanuts and most of them significantly decreased mycelial growth and AFs production levels by >90 %. These results showed a wide distribution of biological control bacteria against AFs in Chinese peanut main producing areas and the selected RAE bacteria could potentially be utilized for the biocontrol of toxicogenic fungi.