Aims: Pyrodinium bahamense var. compressum is one of the principal causal agents of harmful algal blooms (HABs) in the coastal waters of Sabah, Malaysia. Seafood and aquaculture products tainted with lethal concentrations of the principal neurotoxin, saxitoxin, have been implicated in mortality and morbidity. The bacteria-algae association may play a key role in paralytic shellfish toxin (PST) production during a toxic bloom event. The production of PST during a harmful bloom is unclear and research on the bacterial diversity associated with Sabah P. bahamense is scarce. The present study examined the cultivable bacteria diversity associated with P. bahamense through 16S ribosomal RNA (rRNA) gene sequence analysis. Methodology and results: The V3-V4 region of the 16S rRNA gene sequence was amplified and used to identify bacterial populations associated with P. bahamense var. compressum. A total of 62 isolates were successfully isolated, belonging to three different phyla, which were Proteobacteria; 55 (89%), Bacteroidetes; 6 (10%) and Actinobacteria; 1 (1%). Out of 55 Proteobacteria, 27 isolates were gamma-Proteobacteria (Marinobacter salsuginis) and 28 of the isolates were alpha-Proteobacteria; Mameliella atlantica (13), Roseibium denhamense (10) and Roseibium hamelinense (5). The remaining bacteria isolates from the phyla Bacteroidetes and Actinobacteria were identified as Muricauda lutimaris (6) and Micrococcus luteus (1), respectively. Conclusion, significance and impact of study The analysis of the bacterial 16S rRNA gene revealed multiple bacterial taxa associated with the toxic P. bahamense var. compressum bloom. The findings of the present work will pave the way for further studies aimed at isolating and characterizing genes involved in the saxitoxin biosynthesis in the associated bacteria.
Bacteria--metabolism ; Genes, rRNA

Extracellular vesicles (EVs), also known as membrane vesicles, are vesicular bodies secreted by eukaryotic cells and bacteria. EVs can carry proteins, DNA, RNA, and various metabolites for the exchange and transmission of substances between cells. They play contents-dependent physiological functions, such as delivering nutrients, participating in immune response, and treating cancers. Currently, most studies focus on the exploration of vesicles secreted by eukaryotic cells and gram-negative bacteria, while few studies focus on gram-positive bacteria. This review summarized the production, content composition, physiological function, and engineering of EVs secreted by gram-positive bacteria, and prospected future perspectives in this area.
Bacteria/metabolism* ; Extracellular Vesicles/metabolism* ; Gram-Negative Bacteria ; Gram-Positive Bacteria/metabolism* ; Proteins/metabolism*

OBJECTIVEIn this study, we examined the biodegradation of Dichloroethylene (DCE) by two strains of aerobic bacteria.

METHODSUsing batch experiments, we measured the biodegradation rates of DCE and the residual concentrations of DCE for each bacterial strain. The varying trends in biodegradation rates with different initial concentrations of DCE were fitted to kinetic models.

RESULTSThe biodegradation kinetics of DCE by the strain DT-X, which uses toluene as co-metabolic substrate, fitted the Monod model (corresponding parameters: v(max)=0.0075 h(-1), K(s)=2.12 mg/L). The biodegradation kinetics of DCE by the strain DT-M, which uses 1,1-Dichloroethylene as single substrate, fitted the Haldane model (parameters: v(max) =0.0046 h(-1), K(s)=4.25 mg/L, K(i)=8.47 mg/L).

CONCLUSIONThe substrate removal rate constant of 1,1-Dichloroethylene of the co-metabolic strain DT-X was much higher than that of strain DT-M. The substrate removal rates obtained from both bacterial strains in this study were higher than those reported in similar studies.

Lipid Droplets/metabolism* ; Bacteria ; Lipid Metabolism

Bacteria ; cytology ; metabolism ; Quorum Sensing ; Signal Transduction

Polyethylene (PE) is the most abundantly used synthetic resin and one of the most resistant to degradation, and its massive accumulation in the environment has caused serious pollution. Traditional landfill, composting and incineration technologies can hardly meet the requirements of environmental protection. Biodegradation is an eco-friendly, low-cost and promising method to solve the plastic pollution problem. This review summarizes the chemical structure of PE, the species of PE degrading microorganisms, degrading enzymes and metabolic pathways. Future research is suggested to focus on the screening of high-efficiency PE degrading strains, the construction of synthetic microbial consortia, the screening and modification of degrading enzymes, so as to provide selectable pathways and theoretical references for PE biodegradation research.
Polyethylene/metabolism* ; Bacteria/metabolism* ; Plastics/metabolism* ; Biodegradation, Environmental ; Microbial Consortia

PET (polyethylene terephthalate) is one of the most important petrochemicals that is widely used in mineral water bottles, food and beverage packaging and textile industry. Because of its stability under environmental conditions, the massive amount of PET wastes caused serious environmental pollution. The use of enzymes to depolymerize PET wastes and upcycling is one of the important directions for plastics pollution control, among which the key is the depolymerization efficiency of PET by PET hydrolase. BHET (bis(hydroxyethyl) terephthalate) is the main intermediate of PET hydrolysis, its accumulation can hinder the degradation efficiency of PET hydrolase significantly, and the synergistic use of PET hydrolase and BHET hydrolase can improve the PET hydrolysis efficiency. In this study, a dienolactone hydrolase from Hydrogenobacter thermophilus which can degrade BHET (HtBHETase) was identified. After heterologous expression in Escherichia coli and purification, the enzymatic properties of HtBHETase were studied. HtBHETase shows higher catalytic activity towards esters with short carbon chains such as p-nitrophenol acetate. The optimal pH and temperature of the reaction with BHET were 5.0 and 55 ℃, respectively. HtBHETase exhibited excellent thermostability, and retained over 80% residual activity after treatment at 80 ℃ for 1 hour. These results indicate that HtBHETase has potential in biological PET depolymerization, which may facilitate the enzymatic degradation of PET.
Hydrolases/metabolism* ; Bacteria/metabolism* ; Hydrolysis ; Polyethylene Terephthalates/metabolism*

Chlorinated hydrocarbons (CAHs) threaten human health and the ecological environment due to their strong carcinogenic, teratogenic, mutagenic and heritable properties. Heterotrophic assimilation degradation can completely and effectively degrade CAHs, without secondary pollution. However, it is crucial to comprehensively understand the heterotrophic assimilation process of CAHs for its application. Therefore, we review here the characteristics and advantages of heterotrophic assimilation degradation of CAHs. Moreover, we systematically summarize current research status of heterotrophic assimilation of CAHs. Furthermore, we analyze bacterial genera and metabolism, key enzymes and characteristic genes involved in the metabolic process. Finally, we indicate existing problems of heterotrophic assimilation research and future research needs.
Bacteria ; metabolism ; Biodegradation, Environmental ; Hydrocarbons, Chlorinated ; metabolism ; Industrial Microbiology ; trends

To evaluate the ability of microbial mix-culture fermenting syngas into ethanol, we studied the microbial mix-cultures A-fm 4, G-fm 4, Lp-fm 4 and B-fm 4 obtained by enrichment and compared with Clostridium autoethanogenum DSM10061 with 10% and 25% inoculation size. The results show that, with 10% inoculation size, the ethanol production of A-fm 4, G-fm 4, Lp-fm 4, B-fm 4 and C. autoethanogenum were 349.15, 232.16, 104.25, 79.90 and 26.99 mg/L respectively. With 25% inoculation size, the ethanol production were 485.81, 472.73, 348.58, 272.52 and 242.15 mg/L respectively. Higher inoculation size will increase the production of ethanol. The tested mix-culture exhibited a significant yield advantage compared with the maximum production of C. autoethanogenum reported in the literature (259.64 mg/L). This research provided a practical method to improve ethanol production from syngas.
Bacteria ; classification ; metabolism ; Clostridium acetobutylicum ; metabolism ; Ethanol ; isolation & purification ; metabolism ; Fermentation ; Gases ; metabolism ; Hydrogen ; metabolism

Cyclodipeptide (CDP) composed of two amino acids is the simplest cyclic peptide. These two amino acids form a typical diketopiperazine (DKP) ring by linking each other with peptide bonds. This characteristic stable ring skeleton is the foundation of CDP to display extensive and excellent bioactivities, which is beneficial for CDPs' pharmaceutical research and development. The natural CDP products are well isolated from actinomycetes. These bacteria can synthesize DKP backbones with nonribosomal peptide synthetase (NRPS) or cyclodipeptide synthase (CDPS). Moreover, actinomycetes could produce a variety of CDPs through different enzymatic modification. The presence of these abundant and diversified catalysis indicates that actinomycetes are promising microbial resource for exploring CDPs. This review summarized the pathways for DKP backbones biosynthesis and their post-modification mechanism in actinomycetes. The aim of this review was to accelerate the genome mining of CDPs and their isolation, purification and structure identification, and to facilitate revealing the biosynthesis mechanism of novel CDPs as well as their synthetic biology design.
Actinobacteria/metabolism* ; Actinomyces/metabolism* ; Biological Products/metabolism* ; Bacteria/metabolism* ; Diketopiperazines/metabolism* ; Amino Acids