Biology subjects

Xun, L.

Publications and source records attributed to Xun, L..

7 recordsLinked to original sources

bioRxiv2024

Zero valent sulfur is the product of assimilatory sulfite reductase and a substrate of cysteine synthase

The long process of the assimilatory sulfate-reduction consists of sulfate reduction to H2S and then H2S assimilation for cysteine synthesis. However, recent studies indicate that both H2S and zero valent sulfur (S0) are produced during dissimilatory sulfate reduction process, which leads to the question whether S0 also is involved in assimilatory sulfate-reduction. Herein, phylogenetic analysis grouped assimilatory sulfite reductases into five clusters and we re-examined four representatives from two major clusters. These enzymes produced both S0 and H2S from sulfite. However, S0 was more like a direct product, while H2S was just a derivative of S0 via chemical reduction. Phylogenetic analysis of cysteine synthases grouped them into six clusters, and we re-examined six representatives from two major clusters. These enzymes used both glutathione persulfide (GSSH, a common intracellular compound containing a S0 atom) and H2S as substrates to synthesize cysteine, but preferred to use GSSH. These findings indicated that S0, other than H2S, is the key intermediate during the process of inorganic sulfur converting to organic sulfur. ImportanceSulfate reduction is an important link in the global sulfur cycle. Assimilatory sulfate-reduction consists of sulfate-reduction to H2S and then H2S assimilation for cysteine synthesis. This concept was founded in 1950s and has not been challenged until today. In this study, we re-examined four representative assimilatory sulfite reductases (aSiRs) and found that these enzymes directly reduced sulfite to zero valent sulfur (S0). A small portion of produced S0 was reduced to H2S via aSiR-independent chemical reactions. Further, we re-examined six representative cysteine synthases and found that these enzymes used S0 derivative compounds (thiosulfate and glutathione persulfide) as substrates to synthesize cysteine. Thus, S0 is the key intermediate of assimilatory sulfate reduction process, other than H2S.

microbiology↗

bioRxiv2024

Environmental polysulfides promote protein disulfide bond formation of microorganisms growing under anaerobic condition

Polysulfides are rich in anaerobic and microbial metabolism active environments. Anaerobic survival of microorganisms requires the formation of protein disulfide bond (DSB). The relation between environmental polysulfides and anaerobic DSB formation has not been studied so far. Herein, we discovered that environmental polysulfides can efficiently mediate protein DSB formation of microorganisms under anaerobic condition. We used polysulfides to treat proteins including roGFP2, Trx1, and DsbA under anaerobic condition and found that all three proteins formed intramolecular DSB in vitro. The growth of E. coli {Delta}dsbB was reduced and the amount of its intracellular protein DSB was decreased under anaerobic condition. However, treating the mutant strain with polysulfides recovered the growth and reversed DSB decrease. Treating E. coli {Delta}dsbA with polysulfides promoted DSB formation of its periplasmic roGFP2 and recovered its growth under anaerobic condition. In addition, treating Schizosaccharomyces pombe with polysulfides led to increase of the intracellular protein DSB content. Thus, our study reveals that environmental polysulfides can promote DSB formation independent of the enzymatic DSB mediating system and oxygen. In this aspect, environmental polysulfides are beneficial for the survival of microorganisms in anaerobic habitats. IMPORTANCEHow polysulfides benefit adaption of microorganisms to anaerobic environments are unclear. Our study reveals that environmental polysulfides efficiently facilitate protein DSB formation under anaerobic condition. Polysulfides contain zero valent sulfur atoms (S0), which can be transferred to the thiol group of cysteine residue. This S0 atom gets two electrons from two cysteine residues and becomes reduced H2S, leaving two cysteine residues in disulfide bond form. Anaerobic growth of microorganisms was benefited from the formation of DSB. This finding paves the way for a deeper understanding of the intricate relationship between polysulfides and microorganisms in environmental contexts.

molecular biology↗

bioRxiv2022

Heterotrophic bacteria drive sulfide oxidation in coastal sediments

Sulfate reduction and sulfur oxidation are very active in coastal sediments. They shape the biogeochemistry and microbial ecology at hot places of organic matter metabolism. Different from the well-studied sulfate reduction, sulfur oxidation in coastal sediments is still full of questions. Herein, we investigated the distribution of reduced sulfur compounds in differently layers of coastal sediments at the Yellow sea and found that sulfide (H2S), sulfane sulfur (S0), and thiosulfate mainly accumulated in anaerobic sediments and were mostly oxidized in anoxic and oxic interface in the sediments and the sea water. Bacterial community analysis indicated that heterotrophic bacteria are dominating species in surface sediments and sea water. Metagenome analysis showed that two sulfur-oxidizing genes encoding sulfide:quinone oxidoreductases (SQR) and persufide dioxygenases (PDO), were sharply more abundant than other sulfur-oxidizing genes in the coastal sediments. Since members of the marine Roseobacter clade were dominant in coastal waters and sediments, we studied the sulfur oxidation pathway in the Roseobacter Ruegeria pomeroyi DSS-3 and found that sulfide:quinone oxidoreductase, persulfide dioxygenase, and sulfite-oxidizing enzyme were the main enzymes for the oxidation of H2S, zerovalent sulfur, and sulfite/thiosulfate. This study, for the first time, clarified the dominating function of heterotrophic bacteria in sulfur oxidation in the coastal sediments and sea water. IMPORTANCECoastal sediments are the most productive ecosystems. We performed the microbial community diversity and metagenomic analysis of seawater and coastal sediments of the Yellow Sea and explored the sulfur oxidation process in them. We found that heterotrophic bacteria are dominating species in surface sediments and sea water, sulfide and sulfane sulfur were mostly oxidized in surface sediments, and the genes encoding SQR, PDO, and SOE are abundant. Using Ruegeria pomeroyi DSS-3 as the model strain, we studied how these enzymes cooperate to oxidize H2S to sulfate. Thus, this research revealed the critical role of heterotrophic bacteria in sulfur oxidation in coastal sediments and sea water.

microbiology↗

bioRxiv2022

Sulfane sulfur post-translationally modifies the global regulator AdpA to influence actinorhodin production and morphological differentiation of Streptomyces coelicolor

The transcription factor AdpA is a key regulator controlling both secondary metabolism and morphological differentiation in Streptomyces. Due to its critical functions, its expression undergoes multi-level regulations at transcriptional, post-transcriptional, and translational levels, yet no post-translational regulation has been reported. Sulfane sulfur, such as organic polysulfide (RSnH, n[≥]2), is common inside microorganisms, but its physiological functions are largely unknown. Herein, we discovered that sulfane sulfur post-translationally modifies AdpA in S. coelicolor via specifically reacting with Cys62 of AdpA to form a persulfide (Cys62-SSH). This modification decreases the affinity of AdpA to its self-promoter PadpA, allowing increased expression of adpA, further promoting the expression of its target genes actII-4 and wblA. ActII-4 activates actinorhodin biosynthesis and WblA regulates morphological development. Bioinformatics analyses indicated that AdpA-Cys62 is highly conserved in Streptomyces, suggesting the prevalence of such modification in this genus. Thus, our study unveils a new type of regulation on the AdpA activity and sheds a light on how sulfane sulfur stimulates the production of antibiotics in Streptomyces. IMPORTANCEStreptomyces produce myriad of polyketide compounds having (potential) clinical applications. While the database of polyketide gene clusters are quickly expanding, the regulation mechanisms of them are rarely known. Sulfane sulfur species are commonly present in microorganisms with unclear functions. Herein, we discovered that sulfane sulfur increases actinorhodin (ACT) production in S. coelicolor. The underlying mechanism is sulfane sulfur specifically reacts with AdpA, a global transcription factor controlling both ACT gene cluster and morphological differentiation related genes, to form sulfhydrated AdpA. This modification changes dynamics of AdpA-controlled gene network and leads to high expression of ACT biosynthetic genes. Given the wide prevalence of AdpA and sulfane sulfur in Streptomyces, this mechanism may represent a common regulating pattern of polyketide gene clusters. Thus, this finding provides a new strategy for mining and activating valuable polyketide gene clusters.

microbiology↗

bioRxiv2021

Rhodanese Rdl2 produces reactive sulfur species to scavenge hydroxyl radical and protect mitochondria

During aerobic respiration, mitochondria generate superoxide anion (O2*-), hydrogen peroxide (H2O2), and hydroxyl radical (HO*), and these reactive oxygen species (ROS) are detrimental to mitochondria. Mitochondrial damage is linked to a broad spectrum of pathologies such as Alzheimers disease, hemochromatosis, and diabetes. Mitochondria contain several enzymes for rapidly removing superoxide anion and hydrogen peroxide, but how they antagonize HO* is elusive, representing a loophole in the anti-ROS system. Herein, we discovered that Rhodanese 2 (Rdl2) is critical for maintaining the functionality and integrity of mitochondria under sub-lethal ROS stress in Saccharomyces cerevisiae. Rdl2 converts stable sulfur species (thiosulfate and dialkyl polysulfide) to reactive sulfane sulfur including persulfide that protects mitochondrial DNA via scavenging HO*. Surprisingly, hydrogen sulfide (H2S) promotes HO* production through stimulating the Fenton reaction, leading to increased DNA damage. Our study may reveal an ex-ante mean for antagonizing HO*, patching the loophole of the anti-ROS system in mitochondria.

microbiology↗

bioRxiv2019

OxyR senses reactive sulfane sulfur and activates genes for its removal in Escherichia coli

Reactive sulfane sulfur species such as hydrogen polysulfide and organic persulfide are newly recognized as normal cellular components, involved in signaling and protecting cells from oxidative stress. Their production is extensively studied, but their removal is less characterized. Herein, we showed that reactive sulfane sulfur is toxic at high levels, and it is mainly removed via reduction by thioredoxin and glutaredoxin with the release of H2S in Escherichia coli. OxyR is best known to respond to H2O2, and it also played an important role in responding to reactive sulfane sulfur under both aerobic and anaerobic conditions. It was modified by hydrogen polysulfide to OxyR C199-SSH, which activated the expression of thioredoxin 2 and glutaredoxin 1. This is a new type of OxyR modification. Bioinformatics analysis showed that OxyRs are widely present in bacteria, including strict anaerobic bacteria. Thus, the OxyR sensing of reactive sulfane sulfur may represent a conserved mechanism for bacteria to deal with sulfane sulfur stress.

microbiology↗

bioRxiv2018

Synthesis of three major auxins from glucose in Engineered Escherichia coli

Indole-3-acetic acid (IAA) is considered the most common and important naturally occurring auxin in plants and a major regulator of plant growth and development. In addition, phenylacetic acid (PAA) and 4-hydroxyphenylacetic acid (4HPA) can also play a role as auxin in some plants. In recent years, several microbes have been metabolically engineered to produce IAA from L-tryptophan. In this study, we showed that aminotransferase aro8 and decarboxylase kdc from Saccharomyces cerevisiae, and aldehyde dehydrogenase aldH from Escherichia coli have broad substrate ranges and can catalyze the conversion of three kinds of aromatic amino acids (L-tryptophan, L-tyrosine or L-phenylalanine) to the corresponding IAA, 4HPA and PAA. Subsequently, three de novo biosynthetic pathways for the production of IAA, PAA and 4HPA from glucose were constructed in E. coli through strengthening the shikimate pathway. This study described here shows the way for the development of agricultural microorganism for biosynthesis of plant auxin and promoting plant growth in the future.

bioengineering↗