Research in microbiology最新文献

Many acidophilic iron-oxidizing bacteria used in the mining industry for the bioleaching of sulfidic minerals are intolerant to high chloride concentrations, resulting in problems where chloride occurs in the deposit at high concentrations or only seawater is available. In search for strains tolerating such conditions a tetrathionate- and iron-oxidizing bacterium was isolated from a tailings-contaminated beach sample at Portman Bay, Cartagena-La Union mining district, Spain, in the presence of 20 g l⁻¹ (0.34 M) sodium chloride. The isolate was able to form spores, did not grow in the absence of NaCl, and oxidized ferrous iron in the presence of up to 1.5 M (∼87 g l⁻¹) NaCl. Genome sequencing based on a combination of Illumina and PacBio reads revealed two contigs, a circular bacterial chromosome of 5.2 Mbp and a plasmid of 90 kbp, respectively. The chromosome comprised seven different 16S rRNA genes. Submission of the chromosome to the Type (Strain) Genome Server (TYGS) without preselection of similar sequences revealed exclusively type strains of the genus Alicyclobacillus. In the TYGS analyses the respective most similar species were dependent on whether the final tree was derived from just 16S rRNA, from the genomes, or from the proteomes. Thus, TYGS analysis clearly showed that isolate SO9 represents a novel species of the genus Alicyclobacillus. In the presence of artificial seawater with almost 0.6 M chloride, the addition of Alicyclobacillus sp. SO9 improved copper dissolution from chalcopyrite (CuFeS₂) compared to abiotic leaching without bacteria. The new isolate SO9, therefore, has potential for bioleaching at elevated chloride concentrations.

Metabolic rearrangements that occur during depletion of essential nutrients can lead to accumulation of potentially dangerous metabolites. Here we showed that depletion of phosphate (P_i), accompanied by a sharp inhibition of growth and respiration, caused a transient excess of intracellular cysteine due to a decrease in the rate of protein synthesis. High cysteine level can be dangerous due to its ability to produce ROS and reduce Fe³⁺ to Fenton-reactive Fe²⁺. To prevent these negative effects, excess cysteine was mainly incorporated into glutathione (GSH), the intracellular level of which increased by 3 times, and was also exported to the medium and partially degraded to form H₂S with participation of 3-mercaptopyruvate sulfotransferase (3MST). The addition of P_i to starving cells led to a sharp recovery of respiration and growth, GSH efflux into the medium and K⁺ influx into the cells. A pronounced coupling of P_i, GSH, and K⁺ fluxes was shown upon P_i depletion and addition, which may be necessary to maintain the ionic balance in the cytoplasm. We suggest that processes aimed at restoring cysteine homeostasis may be an integral part of the universal response to stress under different types of stress and for different types of bacteria.

One of the foremost report of apoptosis-like programmed cell death (PCD) came from Xanthomonas axonopodis pv. glycines (Xag), which displayed rapid post-exponential cell death in PCD inducing media (PIM) but not in a non-inducing media (PNIM). The current study aims to decipher for the first time, the advantages of the existence of PCD in this phytopathogenic microorganism. Analysis of RNA-seq under inducing and non-inducing conditions, revealed differential expression of a number of genes related to key physiology of Xag, such as, motility, xanthan biosynthesis and export as well as virulence. A PCD negative mutant Xag M42 displayed diminished virulence and a contrasting transcriptome pattern. In vitro experiments revealed that under PCD inducing condition, Xag produced negligible xanthan gum as well as extracellular amylase, displayed enhanced swarming motility, released copious e-DNA and formed scanty biofilm. Lack of ‘diffusible signalling factor’ production was eliminated as possible reason for PCD-induction. Altogether, it appears that, in planta existence of the pathogen metabolically resembles PNIM, and on being transferred to PIM, the cells experience oxidative stress and circumvents it by adopting PCD as an altruistic response. Survival of the remaining population is encouraged by upregulating motility, detachment from the fragile biofilm to achieve dispersal.

DNA integrity in bacteria is regulated by various factors that act on the DNA. trans-translation has previously been shown to be important for the survival of Escherichia coli cells exposed to certain DNA-damaging agents. However, the mechanisms underlying this sensitivity are poorly understood. In this study, we explored the involvement of the trans-translation system in the maintenance of genome integrity using various DNA-damaging agents and mutant backgrounds. Relative viability assays showed that SsrA-defective cells were sensitive to DNA-damaging agents, such as nalidixic acid (NA), ultraviolet radiation (UV), and methyl methanesulfonate (MMS). The viability of SsrA-defective cells was rescued by deleting sulA, although the expression of SulA was not more pronounced in SsrA-defective cells than in wild-type cells. Live cell imaging using a Gam-GFP fluorescent reporter showed increased double-strand breaks (DSBs) in SsrA-defective cells during DNA damage. We also showed that the ribosome rescue function of SsrA was sufficient for DNA damage tolerance. DNA damage sensitivity can be alleviated by partial uncoupling of transcription and translation by using sub-lethal concentrations of ribosome inhibiting antibiotic (tetracycline) or by mutating the gene coding for RNase H (rnhA). Taken together, our results highlight the importance of trans-translation system in maintaining genome integrity and bacterial survival during DNA damage.

Sun exposure is harmful to the skin and increases the risk of skin aging and skin cancer. Here we examined the effects of daily exposure to sun radiation on the skin microbiome in order to determine whether skim microbiome bacteria can contribute to protection from solar damage. Skin swabs were collected from ten lifeguards before and after the summer to analyse the skin microbiome. The results indicate that specific skin microbiome bacteria were enriched following the seasonal sun exposure. Especially interesting were two bacterial families - Sphingomonas and Erythrobacteraceae – which may have the ability to protect against UV radiation as they produce potentially protective compounds. We concentrated on a Sphingomonas strain and could show that it was highly resistant to UV irradiation and was able to reduce reactive oxygen species levels in human keratinocytes. These results provide a proof-of-concept for the role of the skin microbiome in protection from solar radiation.

The opportunistic human pathogen Bacillus cereus controls the expression of key infection-promoting phenotypes using bacterial quorum sensing (QS). QS signal transduction within the species is controlled by an autoinducing peptide, PapR₇, and its cognate receptor, PlcR, indicating that the PlcR:PapR interface is a prime target for QS inhibitor development. The C-terminal region of the peptide (PapR₇; ADLPFEF) has been successfully employed as a scaffold to develop potent QS modulators. Despite the noted importance of the C-terminal carboxylate and amide protons in crystallographic data, their role in QS activity has yet to be explored. In this study, an N-methyl scan of PapR₇ was conducted in conjunction with a C-terminal modification of previously identified B. cereus QS inhibitors. The results indicate that the amide proton at Glu6 and the C-terminal carboxylate are important for effective QS inhibition of the PlcR regulon. Through β-galactosidase and hemolysis assays, a series of QS inhibitors were discovered, including several capable of inhibiting QS with nanomolar potency. These inhibitors, along with the structure–activity data reported, will serve as valuable tools for disrupting the B. cereus QS pathway towards developing novel anti-infective strategies.

Sulfolobus acidocaldarius, a thermoacidophilic crenarchaeon, frequently encounters temperature fluctuations, oxidative stress, and nutrient limitations in its environment. Here, we employed a high-throughput transcriptomic analysis to examine how the gene expression of S. acidocaldarius changes when exposed to high temperatures (92 °C). The data obtained was subsequently validated using quantitative reverse transcription-PCR (qRT-PCR) analysis. Our particular focus was on genes that are involved in the heat shock response, type-II Toxin-Antitoxin systems, and putative transcription factors. To investigate how S. acidocaldarius adapts to multiple stressors, we assessed the expression of these selected genes under oxidative and nutrient stresses using qRT-PCR analysis. The results demonstrated that the gene thβ encoding the β subunit of the thermosome, as well as hsp14 and hsp20, play crucial roles in the majority of stress conditions. Furthermore, we observed overexpression of at least eight different TA pairs belonging to the type II TA systems under all stress conditions. Additionally, four common transcription factors: FadR, TFEβ, CRISPR loci binding protein, and HTH family protein were consistently overexpressed across all stress conditions, indicating their significant role in managing stress. Overall, this work provides the first insight into molecular players involved in the cross-stress adaptation of S. acidocaldarius.

Leptospirosis, a global reemerging zoonosis caused by the spirochete Leptospira, has severe human and veterinary implications. Cell wall hydrolase (LIC_10271) with LytM (peptidase M23) and LysM domains are found to be associated with various pathogenic bacteria. These domains regulate effects on extracellular matrix and biofilm components, which promote cell wall remodeling and pathogen dissemination in the host. In this study, we present the cloning, expression, purification, and characterization of LIC_10271. To determine the localization of LIC_10271 within the inner membrane of Leptospira, Triton X-114 subcellular fractionation and immunoblot studies were performed. Furthermore, r-LIC_10271 binds with peptidoglycan, lipopolysaccharide, and laminin in a dose-dependent manner. Analysis of the signal peptide, M23, and LysM domains revealed conservation primarily within the P1 group of Leptospira, which encompasses the most pathogenic species. Moreover, the presence of native-LIC_10271 in the inner membrane and the distribution of M23 and LysM domains across pathogenic strains indicates their potential involvement in the interaction between the host and Leptospira.