Operating bioreactors for microbial exopolysaccharide production

There is considerable interest in exploiting the novel physical and biological properties of microbial exopolysaccharides in industry and medicine. For economic and scientific reasons, large scale production under carefully monitored and controlled conditions is required. Producing exopolysaccharides in industrial fermenters poses several complex bioengineering and microbiological challenges relating primarily to the very high viscosities of such culture media, which are often exacerbated by the producing organism’s morphology. What these problems are, and the strategies for dealing with them are discussed critically in this review, using pullulan, curdlan, xanthan, and fungal β-glucans as examples of industrially produced microbial exopolysaccharides. The role of fermenter configuration in their production is also examined.     

Operating bioreactors for microbial exopolysaccharide production

There is considerable interest in exploiting the novel physical and biological properties of microbial exopolysaccharides in industry and medicine. For economic and scientific reasons, large scale production under carefully monitored and controlled conditions is required. Producing exopolysaccharides in industrial fermenters poses several complex bioengineering and microbiological challenges relating primarily to the very high viscosities of such culture media, which are often exacerbated by the producing organism's morphology. What these problems are, and the strategies for dealing with them are discussed critically in this review, using pullulan, curdlan, xanthan, and fungal β-glucans as examples of industrially produced microbial exopolysaccharides. The role of fermenter configuration in their production is also examined.     

Chemical characterization of exopolysaccharides from the marine fouling diatom amphora coffeaeformis

Amphora coffeaeformis cells were grown in batch cultures under continuous illumination at 18°C for 10 d. Algal cells were removed by centrifugation, lyophilized and used for the extraction of exopolysaccharides using either 0.05 M EDTA, 1 M NaOH or 1.5 M NaCl. The 1.5 M NaCl treatment removed most exopolysaccharides. Glucose (81%) was the most abundant monosaccharide in the exopolysaccharides. The chemical composition data suggest that the exopolymers were acidic sulphated polysaccharides containing high concentrations of pyruvate (22%) and uronic acids (18%). These polysaccharides may play an important role in metal complexation and protection from desiccation in A. coffeaeformis.     

Exopolysaccharide production by free and immobilized microbial cultures

The batch production of different exopolysaccharides (alginate, xanthan, pullulan, dextran) by free and immobilized microbial cultures was investigated. First, conventional free-cell cultures were performed to obtain control fermentation parameters and macromolecular characteristics of exopolysaccharides. Then microbial cultures were immobilized in composite agar layer/microporous membrane structures and tested for polysaccharide production. The immobilized-cell system proved unsuitable for xanthan and pullulan production. Owing to the fouling of the microporous membrane by the polysaccharide, dextran production by immobilized Leuconostoc mesenteroides also was inefficient. More promising results have been obtained with immobilized Azotobacter vinelandii cultures. The amount of alginate produced by immobilized A. vinelandii represented about 60% of that recovered from a free-cell culture, whereas the polysaccharide yield reached 35% instead of 9% for the free counterpart. These results are compared to the macromolecular characteristics of exopolysaccharides.     

Colanic acid is an exopolysaccharide common to many enterobacteria isolated from paper-machine slimes

In this study, polysaccharide-producing bacteria were isolated from slimes collected from two Finnish and one Spanish paper mill and the exopolysaccharides (EPSs) produced by 18 isolates were characterised. Most of the isolates, selected on the bases of slimy colony morphology, were members of the family Enterobacteriaceae most frequently belonging to the genera Enterobacter and Klebsiella including Raoultella. All of the EPSs analysed showed the presence of charged groups in the form of uronic acid or pyruvate revealing the polyanionic nature of these polysaccharides. Further results of the carbohydrate analysis showed that the EPS produced by nine of the enterobacteria was colanic acid.     

Biosynthesis of the polysialic acid capsule inEscherichia coli K1

The extracellular polysaccharides elaborated by most or all bacterial species function in cell-to-cell and cell-substratum adhesion, cell signaling, and avoidance or inhibition of noxious agents in animal hosts or free-living environments. Recent advances in our understanding of exopolysaccharide synthesis have been facilitated by comparative approaches in both plant and animal pathogens, as well as in microorganisms of industrial importance. One of the best understood of these systems is thekps locus for polysialic acid synthesis inEscherichia coli K1. The genes for sialic acid synthesis, activation, polymerization and translocation have been identified and assigned at least tentative functions in the synthetic and export pathways. Initial studies ofkps thermoregulation suggest that genetic control mechanisms will be involved which are distinct from those already described for several other exopolysaccharides. Information about the common as well as unique features of polysialic acid biosynthesis will increase our knowledge of microbial cell surfaces which in turn may suggest novel targets for therapeutic or industrial interventions.     

Potentials of Exopolysaccharides from Lactic Acid Bacteria

Recent research in the area of importance of microbes has revealed the immense industrial potential of exopolysaccharides and their derivative oligosaccharides from lactic acid bacteria. However, due to lack of adequate technological knowledge, the exopolysaccharides have remained largely under exploited. In the present review, the enormous potentials of different types of exopolysaccharides from lactic acid bacteria are described. This also summarizes the recent advances in the applications of exopolysaccharides, certain problems associated with their commercial production and the remedies.     

阿魏酸酯酶基因克隆表达调控及其应用进展

阿魏酸酯酶作为微生物降解植物多糖的酶系的一部分,其从细胞壁中降解多糖获得芳香酸和单多糖的能力越来越受到重视.主要介绍了阿魏酸酯酶研究进展,包括阿魏酸酯酶的研究现状,酶-底物分子对接模型、阿魏酸酯酶基因克隆表达、重组与调控以及应用.     

Characterization of exopolysaccharides produced by seven biofilm-forming cyanobacterial strains for biotechnological applications

The molecular identification of seven biofilm-forming cyanobacteria and the characterization of their exopolysaccharides were made and considered in terms of potential biotechnological applications. The studied strains were isolated from phototrophic biofilms taken from various Italian sites including a wastewater treatment plant, an eroded soil, and a brackish lagoon. The polysaccharides were characterized by use of ion exchange chromatography, circular dichroism, and cytochemical stains. All strains produced exopolysaccharides with differing ratios of hydrophobic and hydrophilic moieties depending on the species, the polysaccharide fraction (i.e., whether capsular or released), and the ambient conditions. It was shown that the anionic nature of the exopolysaccharides was due to the presence of carboxylic and sulfated groups and is likely the main characteristic with industrial applicability. Potential biotechnological applications are discussed.     

Bacterial exopolysaccharides produced by newly discovered bacteria belonging to the genus Halomonas, isolated from hypersaline habitats in Morocco

We have studied the exopolysaccharides (EPS) from a new group of moderately halophilic bacteria belonging to the genus Halomonas. The quantity of EPS produced, its chemical composition and physical properties depend greatly upon the bacterial strain. The majority of the polymers produced viscous solutions and/or emulsified different hydrocarbon compounds. The most interesting strain, S-30, produced EPS at 2.8 g/l with a maximum viscosity of 23.5 Pa·5 and exhibited pseudoplastic behavior. This EPS emulsified five hydrocarbons more efficiently than did four control surfactants tested. Its monosaccharide composition was glucose:galactose:manose:glucuronic acid in equimolar ratio. Some two-thirds of the strains tested emulsified crude oil better than control surfactants did. There are many potential industrial applications for polysaccharides with these qualities. Journal of Industrial Microbiology & Biotechnology (2000)24, 374–378. Received 09 August 1999/ Accepted in revised form 23 March 2000     

Electron microscopic detection and in situ characterization of bacterial nanoforms in extreme biotopes

The morphology, ultrastructure, and quantity of bacterial nanoforms were studied in extreme biotopes: East Siberia permafrost soil (1–3 Ma old), petroleum-containing slimes (35 years old), and biofilms from subsurface oil pipelines. The morphology and ultrastructure of microbial cells in natural biotopes in situ were investigated by high-resolution transmission electron microscopy and various methods of sample preparation: ultrathin sectioning, cell replicas, and cryofractography. It was shown that the biotopes under study contained high numbers of bacterial nanoforms (29–43% of the total number of microorganisms) that could be assigned to ultramicrobacteria due to their size (diameter of ≤ 0.3 μm and volume of ≤ 0.014 μm³) and structural characteristics (the presence of the outer and cytoplasmic membranes, nucleoid, and cell wall, as well as their division patterns). Seven different morphostructural types of nanoforms of vegetative cells, as well as nanospores and cyst-like cells were described, potentially representing new species of ultramicrobacteria. In petroleum-containing slimes, a peculiar type of nanocells was discovered, gram-negative cells mostly 0.18–0.20 × 0.20–0.30 μm in size, forming in situ spherical aggregates (microcolonies) of dividing cells. The data obtained promoted the isolation of pure cultures of ultramicrobacteria from petroleum-containing slimes; they resembled the ultramicrobacterium observed in situ in their morphology and ultrastructure.     

Shaping the phycosphere: Analysis of the EPS in diatom-bacterial co-cultures

The phycosphere is a unique niche that fosters complex interactions between microalgae and associated bacteria. The formation of this extracellular environment, and the associated bacterial biodiversity, is heavily influenced by the secretion of extracellular polymers, primarily driven by phototrophic organisms. The exopolysaccharides (EPS) represent the largest fraction of the microalgae-derived exudates, which can be specifically used by heterotrophic bacteria as substrates for metabolic processes. Furthermore, it has been proposed that bacteria and their extracellular factors play a role in both the release and composition of the EPS. In this study, two model microorganisms, the diatom Phaeodactylum tricornutum CCAP 1055/15 and the bacterium Pseudoalteromonas haloplanktis TAC125, were co-cultured in a dual system to assess how their interactions modify the phycosphere chemical composition by analyzing the EPS monosaccharide profile released in the culture media by the two partners. We demonstrate that microalgal–bacterial interactions in this simplified model significantly influenced the architecture of their extracellular environment. We observed that the composition of the exo-environment, as described by the EPS monosaccharide profiles, varied under different culture conditions and times of incubation. This study reports an initial characterization of the molecular modifications occurring in the extracellular environment surrounding two relevant representatives of marine systems.     

Electron microscopic detection and in situ characterization of bacterial nanoforms in extreme biotopes

The morphology, ultrastructure, and quantity of bacterial nanoforms were studied in extreme biotopes: East Siberia permafrost soil (1-3 Ma old), petroleum-containing slimes (35 years old), and biofilms from subsurface oil pipelines. The morphology and ultrastructure of microbial cells in natural biotopes in situ were investigated by high-resolution transmission electron microscopy and various methods of sample preparation: ultrathin sectioning, cell replicas, and cryofractography. It was shown that the biotopes under study contained high numbers of bacterial nanoforms (29-43% of the total number of microorganisms) that could be assigned to ultramicrobacteria due to their size (diameter of < or =0.3 microm and volume of < or =0.014 microm3) and structural characteristics (the presence of the outer and cytoplasmic membranes, nucleoid, and cell wall, as well as their division patterns). Seven different morphostructural types of nanoforms of vegetative cells, as well as nanospores and cyst-like cells were described, potentially representing new species of ultramicrobacteria. In petroleum-containing slimes, a peculiar type of nanocells was discovered, gram-negative cells mostly 0.18-0.20 x 0.20-0.30 microm in size, forming spherical aggregates (microcolonies) of dividing cells in situ. The data obtained promoted the isolation of pure cultures of ultramicrobacteria from petroleum-containing slimes; they resembled the ultramicrobacterium observed in situ in their morphology and ultrastructure.     

Caroteno-protein and exopolysaccharide production by co-cultures of Rhodotorula glutinis and Lactobacillus helveticus

The lactose-negative yeast Rhodotorula glutinis 22P and the homofermentative lactic acid bacterium Lactobacillus helveticus 12A were cultured together in a cheese whey ultrafiltrate containing 42 g L⁻¹ lactose. The chemical composition of the caroteno-protein has been determined. The carotenoid and protein contents are 248  μ g g⁻¹ dry cells and 48.2% dry weight. Carotenoids produced by Rhodotorula glutinis 22P have been identified as β-carotene 15%, torulene 10%, and torularhodin 69%. After separating the cell mass from the microbial association, the exopolysaccharides synthesized by Rhodotorula glutinis 22P were isolated from the supernatant medium in a yield of 9.2 g L⁻¹. The monosaccharide composition of the synthesized biopolymer was predominantly D-mannose (57.5%). Received 08 July 1996/ Accepted in revised form 11 December 1996     

The biology of biofouling diatoms and their role in the development of microbial slimes

Diatoms are a major component of microbial slimes that develop on man-made surfaces placed in the marine environment. Toxic antifouling paints, as well as environmentally friendly, fouling-release coatings, tend to be effective against most fouling organisms, yet fail badly to diatom slimes. Biofouling diatoms have been found to tenaciously adhere to and colonise even the most resistant of artificial surfaces. This review covers the basic biology of fouling marine diatoms, their mechanisms of adhesion and the nature of their adhesives, as well as documenting the various approaches that have been utilised to understand the formation and maintenance of diatom biofouling layers.     

The biology of biofouling diatoms and their role in the development of microbial slimes

Diatoms are a major component of microbial slimes that develop on man-made surfaces placed in the marine environment. Toxic antifouling paints, as well as environmentally friendly, fouling-release coatings, tend to be effective against most fouling organisms, yet fail badly to diatom slimes. Biofouling diatoms have been found to tenaciously adhere to and colonise even the most resistant of artificial surfaces. This review covers the basic biology of fouling marine diatoms, their mechanisms of adhesion and the nature of their adhesives, as well as documenting the various approaches that have been utilised to understand the formation and maintenance of diatom biofouling layers.     

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。     

微生物在食品工业中的热点应用及其进展

微生物在食品工业中得到了越来越广泛的应用。对其主要的研究热点作了综述。主要包括冰核细菌、益生菌、微生物风味剂、微生物防腐剂、微生物增稠剂、微生物油脂等方面。展现出了微生物在食品工业中的应用前景。     

Techniques for the Assessment of Growth of Micro-organisms on Plumbing Materials Used in Contact with Potable Water Supplies

Water samples from plumbing installations have often been of poorer microbiological quality than samples collected from the distribution main. This deterioration is often associated with a musty taste or visible turbidity in the water and slimes have sometimes been observed on water fittings. A technique to assess the ability of plumbing materials to support microbial growth is described and the most common categories of materials capable of supporting growth are identified. The most significant micro-organisms frequently found to grow on unsuitable materials were coliform organisms, especially members of the genus Citrobacter. Aeromonas hydrophila, Pseudomonas aeruginosa and fungi.     

Effects of current velocity on the nascent architecture of stream microbial biofilms

Current velocity affected the architecture and dynamics of natural, multiphyla, and cross-trophic level biofilms from a forested piedmont stream. We monitored the development and activity of biofilms in streamside flumes operated under two flow regimes (slow [0.065 m s(-1)] and fast [0.23 m s(-1)]) by combined confocal laser scanning microscopy with cryosectioning to observe biofilm structure and composition. Biofilm growth started as bacterial microcolonies embedded in extracellular polymeric substances and transformed into ripple-like structures and ultimately conspicuous quasihexagonal networks. These structures were particularly pronounced in biofilms grown under slow current velocities and were characterized by the prominence of pennate diatoms oriented along their long axes to form the hexagons. Microstructural heterogeneity was dynamic, and biofilms that developed under slower velocities were thicker and had larger surface sinuosity and higher areal densities than their counterparts exposed to higher velocities. Surface sinuosity and biofilm fragmentation increased with thickness, and these changes likely reduced resistance to the mass transfer of solutes from the water column into the biofilms. Nevertheless, estimates of dissolved organic carbon uptake and microbial growth suggested that internal cycling of carbon was more important in thick biofilms grown in slow flow conditions. High-pressure liquid chromatography-pulsed amperometric detection analyses of exopolysaccharides documented a temporal shift in monosaccharide composition as the glucose levels decreased and the levels of rhamnose, galactose, mannose, xylose, and arabinose increased. We attribute this change in chemical composition to the accumulation of diatoms and increased incorporation of detrital particles in mature biofilms.