Xiaobo Liu

Repetitive domestication to enhance butanol tolerance and production in Clostridium acetobutylicum through artificial simulation of bio-evolution

To improve butanol tolerance and production in Clostridium acetobutylicum, a novel approach was developed in this study, which was called artificial simulation of bio-evolution (ASBE) based on the evolutionary dynamics and natural selection. Through repetitive evolutionary domestications, a butanol-tolerant strain C. acetobutylicum T64 was obtained, which could withstand 4% (v/v) (compared to 2% of the wild-type) butanol and was accompanied by the increase of butanol production from 12.2g/L to 15.3g/L using corn meal as substrate. Fermentation was also carried out to investigate the relationship between butanol tolerance and ABE production, suggesting that enhancing butanol tolerance could increase butanol production but unlikely improve total ABE production. These results also indicated that the ASBE would be an available and feasible method used in biotechnology for enhancement of butanol tolerance and production.

Enhancement of butanol tolerance and butanol yield in Clostridium acetobutylicum mutant NT642 obtained by nitrogen ion beam implantation

As a promising alternative biofuel, biobutanol can be produced through acetone/butanol/ethanol (ABE) fermentation. Currently, ABE fermentation is still a small-scale industry due to its low production and high input cost. Moreover, butanol toxicity to the Clostridium fermentation host limits the accumulation of butanol in the fermentation broth. The wild-type Clostridium acetobutylicum D64 can only produce about 13 g butanol/L and tolerates less than 2% (v/v) butanol. To improve the tolerance of C. acetobutylicum D64 for enhancing the production of butanol, nitrogen ion beam implantation was employed and finally five mutants with enhanced butanol tolerance were obtained. Among these, the most butanol tolerant mutant C. acetobutylicum NT642 can tolerate above 3% (v/v) butanol while the wide-type strain can only withstand 2% (v/v). In batch fermentation, the production of butanol and ABE yield of C. acetobutylicum NT642 was 15.4 g/L and 22.3 g/L, respectively, which were both higher than those of its parental strain and the other mutants using corn or cassava as substrate. Enhancing butanol tolerance is a great precondition for obtaining a hyper-yield producer. Nitrogen ion beam implantation could be a promising biotechnology to improve butanol tolerance and production of the host strain C. acetobutylicum.

Elimination of the formation of biofilm in industrial pipes using enzyme cleaning technique

Graphical abstract

Optimization of liquid media and biosafety assessment for algae-lysing bacterium NP23.

To control algal bloom caused by nutrient pollution, a wild-type algae-lysing bacterium was isolated from the Baiguishan reservoir in Henan province of China and identified as Enterobacter sp. strain NP23. Algal culture medium was optimized by applying a Placket-Burman design to obtain a high cell concentration of NP23. Three minerals (i.e., 0.6% KNO3, 0.001% MnSO4·H2O, and 0.3% K2HPO4) were found to be independent factors critical for obtaining the highest cell concentration of 10(13) CFU/mL, which was 10(4) times that of the control. In the algae-lysing experiment, the strain exhibited a high lysis rate for the 4 algae test species, namely, Chlorella vulgari, Scenedesmus, Microcystis wesenbergii, and Chlorella pyrenoidosa. Acute toxicity and mutagenicity tests showed that the bacterium NP23 had no toxic and mutagenic effects on fish, even in large doses such as 10(7) or 10(9) CFU/mL. Thus, Enterobacter sp. strain NP23 has strong potential application in the microbial algae-lysing project.

Two Novel Algicidal Isolates Kill Chlorella pyrenoidosa by Inhibiting their Host Antioxidase Activities.

In the biocontrol of harmful algal blooms, there has been considerable interest about the role of algicidal bacteria in algicidal activity. In this experiment, two novel algicidal bacteria (strains NP23 and AM11) against Chlorella pyrenoidosa were isolated from the Baiguishan reservoir in China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strains NP23 and AM11 belonged to Enterobacter cloacae and Gibberella moniliformis, respectively. To further understand the algicidal activities, five parameters including the chlorophyll a content, cell survival rate, superoxide dismutase (SOD) peroxide dismutase (POD), and catalase (CAT) were tested in the C. pyrenoidosa cells after inoculation with the algicidal bacteria Enterobacter cloacae NP23 and Gibberella moniliformis AM11. As a result, the growth of the treated C. pyrenoidosa was significantly restrained with a great decline of chlorophyll a content. Meanwhile, three antioxidase activities of the treated C. pyrenoidosa were initially stimulated from day 1 to day 3 but then dramatically inhibited at low level. These results induced that the oxidative imbalance (i.e., inhibition of antioxidase activities) caused by algicidal bacteria could be the killing agent of the C. pyrenoidosa cells.

Diversity and distribution of Archaea in global estuarine ecosystems

Estuarine ecosystem is a unique geographical transitional zone between freshwater and seawater, harboring a wide range of microbial communities including Archaea. Although a large number of Archaea have been detected in such ecosystem, the global patterns in archaeal diversity and distribution are extremely scarce. To bridge this gap, we carried out a comprehensive survey of archaeal communities using ca. 4000 publicly available archaeal 16S rRNA gene sequences (>300 bp) collected from 24 estuaries in different latitude regions. These sequences were divided into 1450 operational taxonomic units (OTUs) at 97% identity, suggesting a high biodiversity that increased gradually from the high- to low-latitude estuaries. Phylogenetic analysis showed that estuarine ecosystem was a large biodiversity pool of Archaea that was mainly composed of 12 phyla. Among them, the predominant groups were Bathyarchaeota, Euryarchaeota and Thaumarchaeota. Interestingly, archaeal distribution demonstrated a geographical differentiation in that Thaumarchaeota was dominated in the low-latitude estuaries, Bathyarchaeota in the mid-latitude estuaries, and Euryarchaeota in the high-latitude estuaries, respectively. Furthermore, the majority of the most abundant 20 OTUs demonstrated an overrepresented or underrepresented distribution pattern in some specific estuaries or latitude regions while a few were evenly distributed throughout the estuaries. This pattern indicates a potential selectivity of geographical distribution. In addition, the analysis of environmental parameters suggested that latitude would be one of the major factors driving the distribution of archaeal communities in estuarine ecosystem. This study profiles a clear framework on the diversity and distribution of Archaea in the global estuarine ecosystem and explores the general environmental factors that influence these patterns. Our findings constitute an important part of the exploration of the global ecology of Archaea.

Insights into the ecology, evolution, and metabolism of the widespread Woesearchaeotal lineages

BackgroundAs a recently discovered member of the DPANN superphylum, Woesearchaeota account for a wide diversity of 16S rRNA gene sequences, but their ecology, evolution, and metabolism remain largely unknown.ResultsHere, we assembled 133 global clone libraries/studies and 19 publicly available genomes to profile these patterns for Woesearchaeota. Phylogenetic analysis shows a high diversity with 26 proposed subgroups for this recently discovered archaeal phylum, which are widely distributed in different biotopes but primarily in inland anoxic environments. Ecological patterns analysis and ancestor state reconstruction for specific subgroups reveal that oxic status of the environments is the key factor driving the distribution and evolutionary diversity of Woesearchaeota. A selective distribution to different biotopes and an adaptive colonization from anoxic to oxic environments can be proposed and supported by evidence of the presence of ferredoxin-dependent pathways in the genomes only from anoxic biotopes but not from oxic biotopes. Metabolic reconstructions support an anaerobic heterotrophic lifestyle with conspicuous metabolic deficiencies, suggesting the requirement for metabolic complementarity with other microbes. Both lineage abundance distribution and co-occurrence network analyses across diverse biotopes confirmed metabolic complementation and revealed a potential syntrophic relationship between Woesearchaeota and methanogens, which is supported by metabolic modeling. If correct, Woesearchaeota may impact methanogenesis in inland ecosystems.ConclusionsThe findings provide an ecological and evolutionary framework for Woesearchaeota at a global scale and indicate their potential ecological roles, especially in methanogenesis.

Microbial electrocatalysis: Redox mediators responsible for extracellular electron transfer

Redox mediator plays an important role in extracellular electron transfer (EET) in many environments wherein microbial electrocatalysis occurs actively. Because of the block of cell envelope and the low difference of redox potential between the intracellular and extracellular surroundings, the proceeding of EET depends mainly on the help of a variety of mediators that function as an electron carrier or bridge. In this Review, we will summarize a wide range of redox mediators and further discuss their functional mechanisms in EET that drives a series of microbial electrocatalytic reactions. Studying these mediators adds to our knowledge of how charge transport and electrochemical reactions occur at the microorganism-electrode interface. This understanding would promote the widespread applications of microbial electrocatalysis in microbial fuel cells, bioremediation, bioelectrosynthesis, biomining, nanomaterial productions, etc. These improved applications will greatly benefit the sustainable development of the environmental-friendly biochemical industries.

Approaches of Genetic Regulation in Actinomycetes for Antibiotic Synthesis

Chunli Liao1, Xiaobo Liu1,2* and Linna Shan1* 1College of Life Science and Engineering, Henan University of Urban Construction, Pingdingshan 467036, Henan, China 2School of Biological Sciences, The University of Hong Kong, Hong Kong *Corresponding authors: Xiaobo Liu, College of Life Science and Engineering, Henan University of Urban Construction, Henan, China, Tel: 8603752089090; Fax: 8603752089090; E-mail: bolieyliu@hotmail.com