Influence of salt concentration on membrane lipids of halophilic bacteria

Abstract A review of salt-dependent changes in membrane lipid composition of halotolerant, moderately halophilic, and extremely halophilic bacteria is presented. The biosynthetic and regulatory mechanisms underlying the observed changes are discussed. Possible implications for the evolution of extreme halophiles and other Archaebacteria are also discussed.     

Production and function of enzymes of eubacterial halophiles

Abstract This review deals with a number of enzymes produced by various moderate, eubacterial halophiles. The effects of salts on both the production and activities of different enzymes from these organisms have been studied. It is shown that the nature of the anions, as well as the cations can influence the production of different enzymes. The nature of these effects varies for different enzymes, and is not, at present, predictable.     

Characterization of the proteasome from the extremely halophilic archaeon Haloarcula marismortui

A 20S proteasome, comprising two subunits alpha and beta, was purified from the extreme halophilic archaeon Haloarcula marismortui, which grows only in saturated salt conditions. The three-dimensional reconstruction of the H. marismortui proteasome (Hm proteasome), obtained from negatively stained electron micrographs, is virtually identical to the structure of a thermophilic proteasome filtered to the same resolution. The stability of the Hm proteasome was found to be less salt-dependent than that of other halophilic enzymes previously described. The proteolytic activity of the Hm proteasome was investigated using the malate dehydrogenase from H. marismortui (HmMalDH) as a model substrate. The HmMalDH denatures when the salt concentration is decreased below 2 M. Under these conditions, the proteasome efficiently cleaves HmMalDH during its denaturation process, but the fully denatured HmMalDH is poorly degraded. These in vitro experiments show that, at low salt concentrations, the 20S proteasome from halophilic archaea eliminates a misfolded protein.     

Hyperhalophilic archaeal biofilms: growth kinetics,structure, and antagonistic interaction in continuous culture

Biofilms by the hyperhalophilic archaea Halorubrum sp. and Halobacterium sp. were analyzed, and for the first time the progression of structural features and the developmental parameters of these sessile populations are described. Optical slicing and digital analysis of sequential micrographs showed that their three dimensional structure was microorganism dependent. Biofilms of Halobacterium sp. developed in clusters that covered about 30% of the supporting surface at the interface level and expanded over about 86?±?4 μm in thickness, while Halorubrum sp. biofilms covered less than 20% of the surface and reached a thickness of 41?±?1 μm. The kinetics of growth was lower in biofilms, with generation times of 27?±?1 and 36?±?2 h for Halobacterium sp. and Halorubrum sp., respectively, as compared to 8.4?±?0.3 and 14?±?1 h in planktonic cultures. Differences between microorganisms were also observed at the cell morphology level. The interaction between the two microorganisms was also evaluated, showing that Halobacterium sp. can outcompete already established Halorubrum sp. biofilms by a mechanism that might include the combined action of tunnelling swimmers and antimicrobial compounds.     

Transport of Compatible Solutes in Extremophiles

Salt-tolerant as well as moderately halophilic and halophilic organisms have to maintain their turgor. One strategy is to accumulate small organic compounds, compatible solutes, by de novo synthesis or uptake. From a bioenergetic point of view, uptake is preferred over biosynthesis. The transport systems catalyzing uptake of compatible solutes are of primary or secondary nature and coupled to ATP hydrolysis or ion (H+, Na+) symport. Expression of the transporter genes as well as the activity of the transporters is regulated by salinity/osmolarity and one of the key questions is how salinity or osmolarity is sensed and the signal transmitted as far as to gene expression and transporter activation. Recent studies shed light on the nature and the activation mechanisms of solute transporters in extremophiles, and this review summarizes current knowledge on the structure, function and osmo- or salt-regulation of transporters for compatible solutes in extremophiles.     

Diversity of moderately halophilic bacteria producing extracellular hydrolytic enzymes

AIMS: The aim of this study was to determine the diversity of moderately halophilic bacteria with hydrolase activities. METHODS AND RESULTS: Screening bacteria from different hypersaline environments in South Spain led to the isolation of a total of 122 moderately halophilic bacteria able to produce different hydrolases (amylases, DNases, lipases, proteases and pullulanases). These bacteria are able to grow optimally in media with 5-15% salts and in most cases up to 20-25% salts. In contrast to strains belonging to previously described species, that showed very little hydrolase activities, environmental isolates produced a great variety of hydrolases. These strains were identified as members of the genera: Salinivibrio (55 strains), Halomonas (25 strains), Chromohalobacter (two strains), Bacillus-Salibacillus (29 strains), Salinicoccus (two strains) and Marinococcus (one strain), as well as eight non-identified isolates. CONCLUSIONS: Moderately halophilic bacteria are a source of hydrolytic enzymes such as amylases, DNases, lipases, proteases and pullulanases. SIGNIFICANCE AND IMPACT OF THE STUDY: Although most culture collection strains are not able to produce hydrolases, it has been shown that environmental isolates can produce these potentially biotechnological important enzymes.     

Antagonistic Interactions between Stress Factors during the Growth of Microorganisms under Conditions Simulating the Parameters of Their Natural Ecotopes

Two stress factors, hypoxia (microaerobic conditions) and a high salt concentration, if applied simultaneously to aerobic microorganisms, display an antagonistic mode of interaction. As a result, the NaCl level that is usually optimal for moderate halophiles (5–6 %) becomes optimal for the growth of weak halophiles (Rhodococcus erythropolis and Shewanella sp. CN32); the halotolerant yeast Yarrowia lypolytica acquires halophilic properties (with a growth optimum at a NaCl concentration of 10%), and the growth rate of the extremely halophilic Halobacterium salinarum increases at supraoptimal salt concentrations (25–34%). This phenomenon is apparently due to multiple changes in metabolic reactions. In particular, high salt concentrations suppress respiration and the formation of enzymes (superoxide dismutase and catalase) that protect the cell from toxic oxygen species. Therefore, establishment of microaerobic conditions compensates for the loss of these protective mechanisms and enables cell growth at higher salt concentrations than under aerobic conditions. Of some importance can also be the increase in the intracellular concentrations of osmoprotectants caused by the suppression of their intracellular oxidation. The implications of this phenomenon for the ecophysiology of microorganisms (including oil-oxidizing species) and for the classification of weak and moderate halophiles are discussed.     

Comparative metabolic diversity in two solar salterns

The purpose of this study was to compare the metabolic diversity of the whole microbial community in an oligotrophic saltern (Eilat, Israel) and in a saltern with a more enriched source water (Newark, California). Between 1993 and 1998 water samples were taken from selected locations within the solar salterns of the Cargill Solar Salt Plant, Newark, California, and the Israel Salt Co. in Eilat, Israel. To examine the whole community metabolic diversity, we used the 96-well BIOLOG GN^{{ TM}} plates which contain 95 different carbon sources and a control well. Plates from samples containing greater than 15% salt were excluded from the final analyses because of a lack of reproducibility when multiple plates were inoculated with the same sample. The data were analyzed by simple matching coefficient and principal component analysis. Both methods gave similar results. Two major clusters were formed. These could be subdivided into 10 sub-clusters with only three samples from the Newark saltern in December 1997 joining at the 95% similarity level. Most of the inlet and lower salinity samples from the Cargill samples comprised one large subcluster. Several carbon sources were used by 85% of the microbial community from the California samples, while 85% of the Eilat samples had no commonly used carbon sources. These results suggest that ponds in different geographic locations may have communities with different microbial populations despite the similarities in salt content and processing for salt production.     

The pressure relationships of halophilic and non-halophilic prokaryotic cells determined by using gas vesicles as pressure probes

Abstract Gas vesicles can be used to measure the hydrostatic pressure (turgor pressure) in prokaryotic cells. Halophilic cyanobacteria have turgor pressures that are substantially less than those of cyanobacteria from fresh water. Turgor pressure acts so as to tend to burst cell walls and collapse hollow gas vesicles. The halophiles take advantage of their lower turgor pressures by producing cell walls that are relatively thinner and gas vesicles that are relatively wider than in the mesophilic cyanobacteria. In this way the halophilic structure encounters the same stress and saves on material. Extreme halophiles, with negligible turgor, have been able to adopt various shapes and to produce the weakest and widest gas vesicles.     

Membrane binding of ribosomes occurs at SecYE-based sites in the Archaea Haloferax volcanii

Whereas ribosomes bind to membranes at eukaryal Sec61alphabetagamma and bacterial SecYEG sites, ribosomal membrane binding has yet to be studied in Archaea. Accordingly, functional ribosomes and inverted membrane vesicles were prepared from the halophilic archaea Haloferax volcanii. The ability of the ribosomes to bind to the membranes was determined using a flotation approach. Proteolytic pretreatment of the vesicles, as well as quantitative analyses, revealed the existence of a proteinaceous ribosome receptor, with the affinity of binding being comparable to that found in Eukarya and Bacteria. Inverted membrane vesicles prepared from cells expressing chimeras of SecE or SecY fused to a cytoplasmically oriented cellulose-binding domain displayed reduced ribosome binding due to steric hindrance. Pretreatment with cellulose drastically reduced ribosome binding to chimera-containing but not wild-type vesicles. Thus, as in Eukarya and Bacteria, ribosome binding in Archaea occurs at Sec-based sites. However, unlike the situation in the other domains of Life, ribosome binding in haloarchaea requires molar concentrations of salt. Structural information on ribosome-Sec complexes may provide insight into this high salt-dependent binding.     

极端嗜盐菌的特性及其应用前景

主要介绍极端嗜盐菌的嗜盐机理、细菌视紫红质(bR)和嗜盐菌素的研究进展,然后对其在环境生物治理、生物电子和医药工业等领域的应用研究进行总结和展望。     

四氢嘧啶微生物合成与应用研究进展

极端环境微生物定义了生命的边界。为了适应各种极端环境,极端环境微生物通过合成许多独特的活性化合物来保护自己。四氢嘧啶就是其中一种代表性的保护性物质。它最早是从极端嗜盐菌中发现的,作为调节细胞渗透压的一类相容性溶质,可以帮助微生物适应高盐等恶劣环境。研究发现四氢嘧啶不仅是一种重要的渗透压调节剂,还是一种高效的生物保护剂,可以帮助蛋白、核酸、生物膜乃至整个细胞对抗高温、干燥、冷冻和辐射等多种逆境。因此,四氢嘧啶在生物保护、生物医药和生物科技等众多领域展现出广阔的商业化应用前景。随着合成生物学和代谢工程技术的快速发展,传统的嗜盐菌四氢嘧啶生产方法已逐步被产率更高、环境更友好的生物工程菌及技术所取代。本文围绕四氢嘧啶的微生物合成及其应用研究进行综述,为后续四氢嘧啶的开发和应用提供重要参考。     

The question of uniqueness of ancient bacteria

Microorganisms are associated with a variety of ancient geological materials. However, conclusive proof that these organisms are as old as the geological material and not more recent introductions has generally been lacking. Over the years, numerous reports of the isolation of ancient bacteria from geological materials have appeared. Most of these have suffered from the fact that the protocol for the surface sterilization of the sample was either poorly defined, inadequate or rarely included data to validate the overall effectiveness of the sterilization protocol. With proper sterility validation and isolation protocol, a legitimate claim for the isolation of an ancient microbe can be made. Biochemical, physiological, or morphological data indicate that these ancient microbes are not significantly different from modern isolates. As the role (decomposition) of modern and ancient microbes has not changed over time, it is probably unreasonable to expect these organisms to be vastly different. A discussion on the reasons for the homogeneity of ancient and modern microbes is presented. Journal of Industrial Microbiology & Biotechnology (2002) 28, 32–41 DOI: 10.1038/sj/jim/7000174 Received 20 May 2001/ Accepted in revised form 16 June 2001     

Book reviews

Bacteria and the Enhancement of Oil Recovery. V. Moses and D. G. Springham. Applied Science Publishers, Ltd., London, New Jersey, 1982. With 1 figure and 1 table, xi + 178 p. Hardcover. $32.00

Phanerozoic Stromatolites. Case Histories C. Monty (Editor). Springer Verlag, Berlin, Heidelberg, New York, 1981. 249 pp., $52.60.

Symbiosis in Cell Evolution. Life and Its Environment on the Early Earth. Lynn Margulis. W.H. Freeman and Company, San Francisco, 1981. 419 pp. $24.50 hardcover, $14.95 paperback.

The Flavobacterium‐Cytophaga group. Edited by H. Reichen‐bach and O.B. Weeks. GBF Monograph Series, No. 5. Verlag Chemie International, Deerfield Beach, Weinheim, Basel, 1981. xiii, 217 pages with 38 figures and 75 tables. Paperback. $55.00.     

Biochemical changes induced by salt stress in halotolerant bacterial isolates are media dependent as well as species specific

Halophilic bacteria respond to salt stress by regulating the cytosolic pools of organic solutes to achieve osmotic equilibrium. In order to understand the metabolic regulation of these organic solutes, for the first time, we have investigated the effect of salt on growth and biochemical changes in four major moderately halophilic bacterial strains isolated from a saltern region of the Kumta coast, India. The strains under study were Halomonas hydrothermalis VITP9, Bacillus aquimaris VITP4, Planococcus maritimus VITP21, and Virgibacillus dokdonensis VITP14, which exhibited similar salt tolerance (0% to 10% w/v NaCl) with optimal growth at 5% w/v NaCl. Biochemical analysis showed that the total intracellular organic solutes increased significantly with increasing NaCl concentration in the growth medium, and the compositions of the solutes were dependent on the type of strain and also on the nutrient richness of the growth medium. Glutamic acid levels increased in all the strains under salt stress, indicating the significance of glutamic acid as the anionic counterpart of K⁺/Na⁺ ions and precursor for other synthesized nitrogenous osmolytes. Though initial studies were performed with thin-layer chromatography, mass spectrometry was used to identify the major solutes accumulated by the strains under salt stress, such as proline (VITP4), ectoine (VITP14 and VITP9), and sugars (VITP21) under minimal medium and glycine betaine (by all the strains under study) under complex growth medium conditions. Such comparative study on the stress-dependent metabolic differences of different microbes, under identical experimental condition, helps to identify possible bacterial sources for the production of industrially important solutes.     

Characterization of Salicola sp. IC10, a lipase- and protease-producing extreme halophile

In order to explore the diversity of extreme halophiles able to produce different hydrolytic enzymes (amylase, protease, lipase and DNAse) in hypersaline habitats of South Spain, a screening program was performed. A total of 43 extreme halophiles showing hydrolytic activities have been isolated and characterized. The isolated strains were able to grow optimally in media with 15–20% (w/v) total salts and in most cases, growth was detected up to 30% (w/v) total salts. Most hydrolase producers were assigned to the family Halobacteriaceae , belonging to the genera Halorubrum (22 strains), Haloarcula (nine strains) and Halobacterium (nine strains), and three isolates were characterized as extremely halophilic bacteria (genera Salicola, Salinibacter and Pseudomonas ). An extremely halophilic isolate, strain IC10, showing lipase and protease activities and identified as a Salicola strain of potential biotechnological interest, was further studied. The optimum growth conditions for this strain were 15–20% (w/v) NaCl, pH 8.0, and 37 °C. Zymographic analysis of strain IC10 detected the lipolytic activity in the intracellular fraction, showing the highest activity against p -nitrophenyl-butyrate as a substrate in a colorimetric assay, whereas the proteolytic activity was detected in the extracellular fraction. This protease degraded casein, gelatin, bovine serum albumin and egg albumin.