生物混凝土封存二氧化碳及其机理研究进展

在地质系统或生物系统中发生的二氧化碳(CO₂)转化为碳酸钙的过程可以达到封存CO₂的目的。与地质封存相比,生物封存速度较快且价格低廉。目前,已有研究利用微生物,如藻类等,将大气中的CO₂生物封存到土壤中,但藻类是光能自养型微生物,无法在生物混凝土中生存。相比之下,细菌是生物混凝土技术中更好的选择,在生物加气混凝土砖(B-ACB)中,应用细菌封存CO₂的潜力巨大。细菌可以通过加速碳酸化过程来捕获CO₂,这是由于碳酸化过程通过碳酸酐酶(CA酶)和脲酶可以将CO₂转化为碳酸钙(CaCO₃)。从文献中可以看出,采用生物混凝土可通过加速碳化过程吸收CO₂的同时加固自身。细菌加固混凝土的原理是微生物诱导碳酸钙沉淀(MICP),其机制有多种,其中一些已被认可,并运用于混凝土裂缝愈合中。但迄今为止其应用仍具有局限性,尤其是对处于不同环境条件混凝土结构的细菌种类选择。文章根据不同菌种的生存特性总结成表以供相关研究选择参考。     

重金属胁迫下的微生物代谢组学研究进展

微生物的代谢活动易受到环境变化的影响,当环境中存在重金属污染时微生物会通过调节代谢降低自身所受的重金属的毒害。本文通过微生物代谢组学研究探讨重金属胁迫下微生物代谢活动的响应情况,介绍了微生物代谢组学的相关技术和方法,对其应用进行说明;基于重金属对微生物细胞的毒害作用,对重金属胁迫下微生物代谢组学的相关内容进行综述,发现在重金属胁迫下,微生物可以通过增加代谢活动进而产生更多的代谢物质来响应重金属的胁迫,其中微生物产生的胞外聚合物、草酸和柠檬酸等代谢物在微生物响应重金属胁迫中具有重要作用。微生物通过产生相应代谢物不仅使自身可以在重金属胁迫下生存,这些代谢物还可以使环境中重金属有所减少,这对于利用微生物资源修复重金属污染具有重要意义。     

微生物-矿物相互作用及界面显微分析研究进展

微生物-矿物界面的相互作用贯穿着整个生物浸矿过程,在矿物生物浸出中至关重要,受到微生物的代谢特征、矿物表面结构和物质形态及环境条件的多重交叉影响。研究微生物-矿物界面的相互作用相关的微生物选择性吸附、矿物表面元素形态转化和钝化层、微生物铁硫氧化活性和微生物群落以及胞外物质的组成和性质等的演化,有利于了解微生物-矿物界面作用机制及其关键影响因素和影响机制,从而为优化浸出工艺提供科学的理论依据。达到这些目的,界面的(原位)显微分析手段和技术的进步也至关重要。本文对近些年来上述两方面的研究进行了综述。     

生物工程强化微生物电合成转化CO_2的研究进展

微生物电合成(Microbial electrosynthesis,MES)可直接利用电能驱动微生物还原固定CO_2合成多碳化合物,为可再生新能源转化、精细化学品制备和生态环境保护提供新机遇。但是,微生物吸收胞外电极电子速率慢、产物合成效率低和产品品位不高,限制了MES实现工业化应用。在概述阴极电活性微生物吸收胞外电子的分子机制的基础上,重点综述近5年应用生物工程的理论和技术强化MES用于CO_2转化的策略与研究进展,包括改造和调控胞外电子传递通路和胞内代谢途径以及定向构建有限微生物混合培养菌群三方面,阐明了生物工程可有效突破MES中电子传递慢和可用代谢途径相对单一等瓶颈。针对目前生物工程在改进MES所面临的主要问题,从胞外电子传递机理研究、基因工具箱开发、组学技术与现代分析技术联用等角度展望了今后的研究方向。     

MicroRNAs-微生物互作调控机体脂肪代谢研究进展

微生物和microRNAs均参与机体脂肪酸吸收、转运和从头合成,以及脂肪动员和储存等代谢过程的调节.宿主分泌的microRNAs可通过调控微生物生长和代谢影响脂肪代谢.微生物一方面可影响宿主microRNAs分泌,另一方面其自身也可直接分泌microRNAs,并调节宿主的代谢功能.本文综述了microRNAs和微生物对机体脂肪代谢的影响和调控机制,重点探讨了microRNAs和微生物互作调控脂肪代谢的研究进展和作用机制,以期为精准靶向预防或治疗脂肪代谢紊乱相关疾病提供新的思路和依据.     

海洋微生物胞外多糖结构与生物活性研究进展

海洋微生物胞外多糖结构和功能的特异性源于海洋特殊环境,对其研究具有重要的理论和应用价值。综述了海洋微生物胞外多糖的结构及其生物活性研究进展,展望了研究及应用前景。     

产电微生物的筛选方法研究进展

产电微生物是一类具有胞外电子转移能力的微生物,能够将有机物中储存的化学能转化为电能,其作为微生物电催化系统的催化剂,已经成为环境和能源领域的研究热点。但目前所发现的产电菌,产电机制有所差异,产电能力参差不齐,菌株的性能从根本上影响了其产电能力,其产电能力不足成为限制微生物燃料电池在工业上广泛应用的主要瓶颈。目前,通过理性设计或定向进化等改造方法,难以实现产电微生物在复杂多样环境中的广泛应用。通过定向筛选策略,建立一套快速、高效的筛选鉴定技术,挖掘环境中性能优异的产电微生物,是促进其广泛应用的有效途径。文中基于产电微生物的种类,总结回顾了现有的产电微生物的筛选鉴定方法,并对其研究前景进行了展望。     

电活性微生物胞外聚合物的特征与应用

电活性微生物是一类能够通过直接接触、导电菌毛或氧化还原介质与电极或者其他细胞进行胞外电子传递的微生物。而在这个过程中,胞外聚合物(extracellular polymeric substances, EPS)扮演着重要的角色。EPS是微生物生长过程中通过细胞裂解、水解分泌的高分子聚合物的混合物,主要由蛋白质、多糖和腐殖质等物质组成。来自电活性微生物的EPS的不同组成成分和特性会对EPS的电活性以及电活性微生物胞外电子传递产生一定的影响,同时在环境应用方面发挥重要作用。因此,为了更全面了解电活性微生物EPS的电活性及其对电活性微生物胞外电子传递的作用,本文总体介绍了电活性微生物EPS的电活性的直接表征方法,再从组成成分、化学性质、物理性质和空间分布4个方面综述了其对EPS电活性的影响及其在电子传递中的作用,介绍了当前电活性微生物EPS在染料废水脱色、重金属吸附、有机污染物的生物转化和渗滤液管理等方面的环境应用,并从表征方法、试验规模和互作机理研究等角度展望了未来的研究方向。     

矿物电子能量协同微生物胞外电子传递与生长代谢

微生物的电子传递过程在生命进化和生物地球化学循环中发挥着关键作用。近年来,随着微生物电子传递研究的深入开展,微生物纳米导线、导电生物被膜及种间电子传递等多种新型的微生物胞外电子传递机制不断被发现,微生物电子传递的距离也从纳米级拓展至厘米级。这些微生物的长距离电子传递过程环环相扣、相互协同,从而构成长距离电子传递网络,并在物质循环和能量转化中共同发挥作用。微生物长距离电子传递网络的结构功能及其调控机制已成为多个学科共同关注的焦点。本文以电子传递的距离为主线,对不同尺度的微生物长距离电子传递过程及网络研究的新进展进行综述,包括纳米尺度的电子传递网络（周质空间和外膜表层）、微米至毫米尺度的电子传递网络（纳米导线、细胞间电子和导电生物被膜）、厘米尺度的电子传递网络（电缆细菌）等,并分析了该研究现存的主要问题和下一步的发展方向,以期为进一步推进微生物长距离电子传递网络理论和应用研究提供科学参考。     

细菌生物被膜基质的研究进展

细菌生物被膜(biofilm)附着在生物或者非生物表面,由细菌及其分泌的糖、蛋白质和核酸等多种基质组成的细菌群落,是造成病原细菌持续性感染、毒力和耐药性的重要原因之一.细菌的生物被膜基质由复杂的胞外聚合物(extracellular polymeric substances,EPS)构成,影响生物被膜的结构和功能.本文...     

Complexity of cyanobacterial exopolysaccharides: composition, structures, inducing factors and putative genes involved in their biosynthesis and assembly

Cyanobacterial extracellular polymeric substances (EPS) are mainly composed of high-molecular-mass heteropolysaccharides, with variable composition and roles according to the microorganism and the environmental conditions. The number of constituents – both saccharidic and nonsaccharidic – and the complexity of structures give rise to speculations on how intricate their biosynthetic pathways could be, and how many genes may be involved in their production. However, little is known regarding the cyanobacterial EPS biosynthetic pathways and regulating factors. This review organizes available information on cyanobacterial EPS, including their composition, function and factors affecting their synthesis, and from the in silico analysis of available cyanobacterial genome sequences, proposes a putative mechanism for their biosynthesis.     

Effects of environmental factors on microbial induced calcium carbonate precipitation

Aims: To gain an understanding of the environmental factors that affect the growth of the bacterium Sporosarcina pasteurii, the metabolism of the bacterium and the calcium carbonate precipitation induced by this bacterium to optimally implement the biological treatment process, microbial induced calcium carbonate precipitation (MICP), in situ. Methods and Results: Soil column and batch tests were used to assess the effect of likely subsurface environmental factors on the MICP treatment process. Microbial growth and mineral precipitation were evaluated in freshwater and seawater. Environmental conditions that may influence the ureolytic activity of the bacteria, such as ammonium concentration and oxygen availability, as well as the ureolytic activities of viable and lysed cells were assessed. Treatment formulation and injection rate, as well as soil particle characteristics are other factors that were evaluated for impact on uniform induction of cementation within the soils. Conclusions: The results of the study presented herein indicate that the biological treatment process is equally robust over a wide range of soil types, concentrations of ammonium chloride and salinities ranging from distilled water to full seawater; on the time scale of an hour, it is not diminished by the absence of oxygen or lysis of cells containing the urease enzyme. Significance and Impact of Study: This study advances the biological treatment process MICP towards field implementation by addressing key environmental hurdles faced with during the upscaling process.     

A methodological review on the characterization of microalgal biofilm and its extracellular polymeric substances

Biofilm secreted by microalgae are extracellular polymeric substances (EPSs) composed mainly of polysaccharides, proteins, nucleic acids and lipids. These EPSs immobilize the cells and stabilize biofilm, mediating adhesion towards solid surfaces. The EPSs valorization through industrial exploitations and scientific works is becoming more popular, but the bottleneck of such studies is the lack of consensus among researchers on the selection of detection techniques to be used, especially for novice researchers. It is a daunting task for any inexperienced researcher when they fail to identify the right tools needed for microalgal biofilm studies. In this review, a well-refined analysis protocol about microalgal biofilm and EPSs were prepared including its extraction and characterization. Pros and cons of various detection techniques were addressed and cutting-edge methods to study biofilm EPSs were highlighted. Future perspectives were also presented at the end of this review to bridge research gaps in studying biofilm adhesion via EPSs production. Ultimately, this review aims to assist novice researchers in making the right choices in their research studies on microalgal biofilms in accordance to the available technologies and needs.     

Taphonomy of Early Permian benthic assemblages (Carnic Alps, Austria): carbonate dissolution versus biogenic carbonate precipitation

During the Early Permian, in the area of the Carnic Alps, a quartz-gravelly beach fringed a mixed siliciclastic-carbonate lagoon with fleshy algal meadows and oncoids; seaward, an ooid shoal belt graded down dip to a low-energy carbonate inner shelf with phylloid algal meadows. In limestones, foraminiferal biomurae and bioclast preservation record tapholoss by rotting of non-calcified organisms (interpreted as fleshy algae) and by dissolution of aragonitic fossils. Carbonate loss by dissolution was counteracted and, locally, perhaps exceeded by carbonate precipitation of encrusting foraminifera and as oncoids. Sites of abrasion and carbonate dissolution (beach), sites with tapholoss by rotting and dissolution, but with microbialite/foraminiferal carbonate precipitation (lagoon, inner shelf), and sites only of carbonate precipitation (ooid shoals) co-existed on discrete shelf compartments. Compartmentalized, contemporaneous carbonate dissolution and precipitation, to total amounts yet difficult to quantify, impede straightforward estimates of ancient carbonate sediment budget.     

Bacterial biofilms and quorum sensing: fidelity in bioremediation technology

Increased contamination of the environment with toxic pollutants has paved the way for efficient strategies which can be implemented for environmental restoration. The major problem with conventional methods used for cleaning of pollutants is inefficiency and high economic costs. Bioremediation is a growing technology having advanced potential of cleaning pollutants. Biofilm formed by various micro-organisms potentially provide a suitable microenvironment for efficient bioremediation processes. High cell density and stress resistance properties of the biofilm environment provide opportunities for efficient metabolism of number of hydrophobic and toxic compounds. Bacterial biofilm formation is often regulated by quorum sensing (QS) which is a population density-based cell–cell communication process via signaling molecules. Numerous signaling molecules such as acyl homoserine lactones, peptides, autoinducer-2, diffusion signaling factors, and α-hydroxyketones have been studied in bacteria. Genetic alteration of QS machinery can be useful to modulate vital characters valuable for environmental applications such as biofilm formation, biosurfactant production, exopolysaccharide synthesis, horizontal gene transfer, catabolic gene expression, motility, and chemotaxis. These qualities are imperative for bacteria during degradation or detoxification of any pollutant. QS signals can be used for the fabrication of engineered biofilms with enhanced degradation kinetics. This review discusses the connection between QS and biofilm formation by bacteria in relation to bioremediation technology.     

A mechanistic study of in situ chemical cleaning-in-place for a PTFE flat sheet membrane: fouling mitigation and membrane characterization

This study aimed at unfolding the role and mechanisms of chemically enhanced cleaning-in-place (CIP) regimes in fouling control of polytetrafluoroethylene (PTFE) made flat sheet (FS) membrane bio-reactors (MBRs). The trans-membrane pressure (TMP) was successfully maintained below 10 kPa using a daily CIP regime consisting of 100 to 600 mg l^?1 of NaOCl and cake layer resistance control was shown to be critical for effective high-flux MBR operation. In contrast, in the control unit without the CIP, the TMP exceeded 35 kPa at a flux of 40 LMH. The extracellular polymeric substances associated with proteins (EPS_protein) were also controlled effectively with a daily application of the CIP to the fouled membrane. Moreover, the CIP prompted a thinner and looser bio-cake layer on the membrane surface, suggesting that in situ CIP can be a favorable method to control FS membrane fouling at high-flux MBR operation.     

Photosynthesis,Respiration and Exopolymer Calcium-Binding in Biofilm Calcification (Westerhöfer and Deinschwanger Creek,Germany)

The impact of microbial activity on biofilm calcification in aquatic environments is still a matter of debate, especially in settings where ambient water has high CaCO₃ mineral supersaturation. In this study, biofilms of two CO₂-degassing karst-water creeks in Germany, which attain high calcite supersaturation during their course downstream, were investigated with regard to water chemistry of the biofilm microenvironment. The biofilms mainly consisted of filamentous cyanobacteria (Phormidium morphotype) and heterotrophic bacteria (including sulfate-reducing bacteria), which affect the microenvironment and produce acidic exopolymers. In situ and ex situ microelectrode measurements showed that a strong pH increase, coupled with Ca^{2 +} consumption, occurred in light conditions at the biofilm surface, while the opposite occurred in the dark. Calcite supersaturation at the biofilm surface, calculated from ex situ Ca^{2 +} and CO₃ ^2? microelectrode measurements, showed that photosynthesis resulted in high omega values during illumination, while respiration slightly lowered supersaturation values in the dark, compared to values in the water column. Dissociation calculation demonstrated that the potential amount of Ca^{2 +} binding by exopolymers would be insufficient to explain the Ca^{2 +} loss observed, although Ca^{2 +} complexation to exopolymers might be crucial for calcite nucleation. No spontaneous precipitation occurred on biofilm-free limestone substrates under the same condition, regardless of high supersaturation. These facts indicate that photosynthesis is a crucial mechanism to overcome the kinetic barrier for CaCO₃ precipitation, even in highly supersaturated settings.