Occurrence of Cladocera (Crustacea) in subterranean waters in Yugoslavia

Contrary to some localities in France and Spain, Cladocera occur in hypogean waters in Yugoslavia very sporadically. Beside the stygobitic species, Alona hercegovinae from caves and Alona smirnovi from interstitial waters, particularly some other Chydoridae seem to be suited for hypogean life. Chydorus sphaericus, reputed as one of the most euryoecious cladocerans, occurs also the deepest in interstitial waters as well as in caves. Other species, found in hypogean waters are Simocephalus vetulus, Ilyocryptus sordidus, Eurycercus lamellatus, Chydorus ovalis, Leydigia leydigi, Acroperus harpae and Biapertura affnis.     

A novel role for calcite in calcium homeostasis.

Calcium carbonate (CaCO3) minerals are known to be deposited in a wide array of different organisms, ranging from microbes to vertebrates [(1989) On Biomineralization, Oxford University Press, New York]. Calcite, aragonite and vaterite are the major crystalline structural polymorphs of CaCO3 associated with living systems, and participate in a variety of biological functions [(1989) Biomineralization: Chemical and Biochemical Perspectives, VCH Publishers, Weinham, Germany; (1991) Advances in Inorganic Chemistry 36, 137-200]. Here we report on the ability of a soil bacterium to synthesize calcite in a calcium-stressed environment. The elaboration of this exocellular crystalline residue enables the organism to regulate its calcium content. The attainment of calcium homeostasis via the exocellular deposition of bacterial calcite with unique crystal habits is a novel biological phenomenon.     

Community Structure of Subsurface Biofilms in the Thermal Sulfidic Caves of Acquasanta Terme,Italy

We performed a microbial community analysis of biofilms inhabiting thermal (35 to 50°C) waters more than 60 m below the ground surface near Acquasanta Terme, Italy. The groundwater hosting the biofilms has 400 to 830 μM sulfide, <10 μM O₂, pH of 6.3 to 6.7, and specific conductivity of 8,500 to 10,500 μS/cm. Based on the results of 16S rRNA gene cloning and fluorescent in situ hybridization (FISH), the biofilms have low species richness, and lithoautotrophic (or possibly mixotrophic) Gamma- and Epsilonproteobacteria are the principle biofilm architects. Deltaproteobacteria sequences retrieved from the biofilms have <90% 16S rRNA similarity to their closest relatives in public databases and may represent novel sulfate-reducing bacteria. The Acquasanta biofilms share few species in common with Frasassi cave biofilms (13°C, 80 km distant) but have a similar community structure, with representatives in the same major clades. The ecological success of Sulfurovumales-group Epsilonproteobacteria in the Acquasanta biofilms is consistent with previous observations of their dominance in sulfidic cave waters with turbulent water flow and high dissolved sulfide/oxygen ratios.Despite rapid progress in the past decade, the deep subsurface remains one of the least explored microbial habitats on earth. Recent studies illustrate the presence of significant spatial heterogeneity (13, 53) and the strong influence of mineralogy and fluid flow on subsurface microbial biodiversity (9, 16, 31, 61). Data obtained by drilling are complemented by an increasing number of studies that exploit subsurface passages navigable by humans (17). These subsurface passages include caves (14, 46) and mines (22, 32, 47, 52, 57). Approximately 10% of known caves (49) and perhaps more (33) are formed where reduced, sulfidic groundwaters interact with oxidized water descending from surface environments. Limestone dissolution in these groundwater mixing zones results in deep caves that receive few organic inputs from the surface. Due to the presence of both sulfide and oxidants where the groundwaters mix, lithoautotrophic microorganisms thrive and supply the primary productivity for food chains that may include invertebrate and vertebrate animals (11, 23). Interest in these isolated terrestrial chemosynthetic microbial communities is fueled by their potential as model systems for microbial biogeography and as analogs for oxygen-poor, sulfur-rich environments prevalent early in Earth history or on other planets.The sulfidic caves studied by microbiologists to date include Lower Kane Cave in Wyoming (15), Cueva de Villa Luz in Mexico (5, 23), Movile Cave in Romania (7, 28), Parker Cave in Kentucky (4), and the Frasassi caves in Italy (38, 39). The average water temperatures of previously studied sulfidic caves range from 12 to 28°C. In contrast, the groundwater in the Grotta Nuova di Rio Garrafo and associated caves near Acquasanta Terme (Italy) reaches temperatures up to 50°C (M. Mainiero, unpublished results). The Acquasanta caves host conspicuous microbial biofilms that have not been previously investigated, presenting an opportunity to compare subsurface environments with similar energy resources but large differences in temperature.A reconnaissance of the Acquasanta caves (Fig. ​(Fig.1)1) showed that they contain biofilm types also reported in other sulfidic caves, including viscous snottites on walls above the water table (see Fig. S1a, b, and e in the supplemental material), reddish clay-rich deposits (“ragu”) similar to those on walls in Cueva de Villa Luz (see Fig. S1e in the supplemental material), and white biofilms covering sediments below the water table (see Fig. S1d and f in the supplemental material). As in Cueva de Villa Luz, subaerial surfaces in areas with high sulfur gas concentrations are covered with elemental sulfur deposits (see Fig. S1c in the supplemental material). Here, we describe the diversity and community structure of biofilms in the thermal Acquasanta groundwater. In addition, we investigate whether the Acquasanta stream biofilms have a structure consistent with a simple ecological niche model developed for sulfur-oxidizing clades inhabiting nonthermal sulfidic caves (37). The niche model considers aqueous sulfide and oxygen concentrations and hydrodynamic shear and suggests that in turbulently flowing (high shear) waters with high sulfide/oxygen ratios, Epsilonproteobacteria should outcompete filamentous Gammaproteobacteria, such as Beggiatoa and Thiothrix. We find that Acquasanta cave stream biofilms share very few phylotypes in common with other sulfidic caves studied to date and are dominated by Epsilonproteobacteria as predicted by the niche model.Open in a separate windowFIG. 1.(A) Plan view map of the Rio Garrafo caves. (Modified from reference 21 with kind permission from Springer Science+Business Media.) Contour lines indicate surface elevation in meters. (B) Cross section of Grotta Nuova del Rio Garrafo. (Modified from reference 18 with permission of the National Speleological Society.) Black circles indicate sampling locations for biofilms depicted in Fig. S1 in the supplemental material. Arrows indicate flow directions for water (solid) and gas (dashed). Samples analyzed in the current study were collected exclusively at site AS1.     

The end of regressive evolution: examining and interpreting the evidence from cave fishes

The evolution of hypogean fauna in general and hypogean fishes in particular has been controversial. Explanations regarding the reduction or loss of phenotypic characters such as eyes and pigmentation range from neo‐Lamarckism to neutral mutations, with 'regressive evolution' being a catch‐all characterization for such processes. The assumptions required for special evolutionary mechanisms underlying the evolution of cave dwellers have been based on generalizations about the animals and their environments drawn from relatively few observations. The evidence offered for notions such as pre‐adaptation of colonizing fauna and the purported impoverished nutrients in all caves is examined and it appears that the generalizations cannot be supported. Some major accomplishments in field and laboratory studies of hypogean fishes are summarized, including work highlighting developmental phenotypic plasticity. At the end, it is argued that evolution of hypogean fauna can be explained by well‐known mechanisms within the current context of evolutionary biology.     

Modelling calcium carbonate biomineralisation processes

The structure-directing influence of the organic dicarboxylates malonate, succinate, glutarate and adipate as templating species on the hydrothermal formation of CaCO(3) was investigated at different temperatures (60, 80, 90, 120, 150 and 190 degrees C) and with a range of molar ratios of [Ca(2+)]/[templating species] (20, 14.3, 10, 7.7, 5, 1, 0.5 and 0.33). In the presence of the dicarboxylates, one, two or three polymorphs of CaCO(3) - calcite, aragonite and vaterite - could be formed, depending on the reaction conditions. In addition changes in crystal morphology were observed for the CaCO(3) polymorphs depending on the concentration of the template. In contrast, synthesis under ambient conditions of temperature and pressure resulted only in calcite formation, although template-dependent morphological changes were again observed. Crystalline products were all characterized by powder X-ray patterns and SEM (Scanning Electron Microscopy) micrographs. The ambient reactions with the chelating, dinucleating carboxylato ligands H(3)heidi and H(5)hpdta produce more profound changes in calcite morphology. With H(3)heidi rounded calcite crystals with shapes similar to that of otoliths are formed and with H(5)hpdta the formation of microtrumpets of constructed from bundles of nanocrystals of calcite is observed. The possible mode of action of these ligands on calcite formation is discussed in the context of known coordination chemistry with other metal ions.     

Growth of phototrophic biofilms from limestone monuments under laboratory conditions

In the current study, five phototrophic biofilms from different Southern Europe limestone monuments were characterised by molecular techniques and cultivated under laboratory conditions. Phototrophic biofilms were collected from Orologio Tower in Martano (Italy), Santa Clara-a-Velha Monastery and Ajuda National Palace, both in Portugal, and Seville and Granada Cathedrals from Spain. The biofilms were grown under laboratory conditions and periodically sampled in order to monitor their evolution over a three-month period. Prokaryotic communities from natural samples and cultivated biofilms were monitored using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments in conjunction with clone sequencing and phylogenetic analysis. DNA-based molecular analysis of 16S rRNA gene fragments from the natural green biofilms revealed complex and different communities composition with respect to phototrophic microorganisms. The biofilms from Orologio Tower (Martano, Italy) and Santa Clara-a-Velha Monastery (Coimbra, Portugal) were dominated by the microalga Chlorella. The cyanobacterium Chroococcidiopsis was the dominating genus from Ajuda National Palace biofilm (Lisbon, Portugal). The biofilms from Seville and Granada Cathedrals (Spain) were both dominated by the cyanobacterium Pleurocapsa. The DGGE analysis of the cultivated biofilms showed that the communities developed differently in terms of species establishment and community composition during the three-month incubation period. The biofilm culture from Coimbra (Portugal) showed a remarkable stability of the microbial components of the natural community in laboratory conditions. With this work, a multiple-species community assemblage was obtained for further stone colonisation experiments.     

A mineralogical characterization of biogenic calcium carbonates precipitated by heterotrophic bacteria isolated from cryophilic polar regions

Precipitation of calcium carbonate (CaCO_3(s)) can be driven by microbial activity. Here, a systematic approach is used to identify the morphological and mineralogical characteristics of CaCO_3(s) precipitated during the heterotrophic growth of micro‐organisms isolated from polar environments. Focus was placed on establishing mineralogical features that are common in bioliths formed during heterotrophic activity, while in parallel identifying features that are specific to bioliths precipitated by certain microbial phylotypes. Twenty microbial isolates that precipitated macroscopic CaCO_3(s) when grown on B4 media supplemented with calcium acetate or calcium citrate were identified. A multimethod approach, including scanning electron microscopy, high‐resolution transmission electron microscopy, and micro‐X‐ray diffraction (μ‐XRD), was used to characterize CaCO_3(s) precipitates. Scanning and transmission electron microscopy showed that complete CaCO_3(s) crystal encrustation of Arthrobacter sp. cells was common, while encrustation of Rhodococcus sp. cells did not occur. Several euhedral and anhedral mineral formations including disphenoid‐like epitaxial plates, rhomboid‐like aggregates with epitaxial rhombs, and spherulite aggregates were observed. While phylotype could not be linked to specific mineral formations, isolates tended to precipitate either euhedral or anhedral minerals, but not both. Three anhydrous CaCO_3(s) polymorphs (calcite, aragonite, and vaterite) were identified by μ‐XRD, and calcite and aragonite were also identified based on TEM lattice‐fringe d value measurements. The presence of certain polymorphs was not indicative of biogenic origin, although several mineralogical features such as crystal‐encrusted bacterial cells, or casts of bacterial cells embedded in mesocrystals are an indication of biogenic origin. In addition, some features such as the formation of vaterite and bacterial entombment appear to be linked to certain phylotypes. Identifying phylotypes consistent with certain mineralogical features is the first step toward discovering a link between these crystal features and the precise underlying molecular biology of the organism precipitating them.     

Comparative study of electron transport system activity and oxygen consumption of amphipods from caves and surface habitats

1. Respiratory electron transport system (ETS) activity and oxygen consumption were measured at 10 °C for the hypogean amphipods Niphargus stygius (from two epikarst locations) and N. krameri (from a sinking river in a cave) and the epigean amphipod Gammarus fossarum (inhabiting a spring and a river). 2. ETS activity and oxygen consumption were compared between caves and the two surface locations, and between hypogean and epigean amphipods. ETS activities were found not to differ between animals from different locations, or between epigean and hypogean amphipods. As expected, the oxygen consumption of N. krameri and N. stygius was lower than that of G. fossarum. 3. The high ratio between ETS activity and oxygen consumption (ETS/R ratio) showed that N. krameri and N. stygius possess high metabolic potential that can be exploited for energy recovery and rapid restoration of body reserves immediately following the appearance of favourable conditions (food and/or oxygen). In contrast, G. fossarum exhibited a low ETS/R ratio, indicating exploitation of a great proportion of the metabolic potential for standard metabolism. 4. Feeding in N. stygius increased oxygen consumption but not ETS activity, and thus fed N. stygius had a much lower ETS/R ratio than starved ones. 5. A relatively high metabolic potential (i.e. high ETS/R ratio) may be an adaptation to hypogean life in amphipods, in that it improves survival under poor food and/or oxygen conditions.     

Application of molecular genetics and geometric morphometrics to taxonomy and conservation of cave beetles in central Italy

Integration of molecular genetic techniques and geometric morphometrics represent a valuable tool in the resolution of taxonomic uncertainty and the identification of significant units for conservation. We combined mitochondrial DNA cytochrome c oxidase subunit II gene sequence data and geometric morphometric analysis to examine taxonomic status and identify units for conservation in four species of the hypogean beetle Duvalius (Coleoptera, Trechinae) using mainly museum specimens collected in central Italy. Previous taxonomic studies based on morphological traits described several subspecies often inhabiting geographically distinct caves. Phylogenetic analysis identified two well supported monophyletic lineages and a number of different clades with relatively small genetic differences, suggesting a short divergence time in line with known geological history of the study area. Geometric morphometrics, on the other hand, recovered a high level of distinctiveness among specimens. Both genetic and morphometric analyses did not entirely corroborate former taxonomic nomenclature, suggesting possible rearrangements and the definition of evolutionary significant units. Beetles of the genus Duvalius are protected by regional laws and the majority of taxa considered in this study inhabit caves located outside protected areas. Our study advocates the importance of devoting protection efforts to networks of cave ecosystems rather than single locations or species.     

Yunotrechus diannanensis n. gen., n. sp., the first troglobitic trechine (Coleoptera: Carabidae) from a tropical area of China

In the present paper Yunotrechus diannanensis n. gen., n. sp. is described and illustrated from two limestone caves which are close to each other in Wenshan and Maguan counties of southern Yunnan Province, southwestern China. Yunotrechus is an anophthalmoid, not directly related to any hypogean trechine genera hitherto known in Yunnan or in southeastern Asian countries because all of them are aphaenopsoids, with elongated prothorax and tumid propleura. The phylogenetic position of Yunotrechus within Trechinae in China or southeastern Asia remains unclear, although it may be related to Superbotrechus Deuve & Tian 2009, which was recorded from western Hubei Province, central China, and Sichuanotrechus Deuve 2006, which was recorded from northern Sichuan Province, southwestern China. Y. diannanensis n. sp. is the first troglobitic trechine beetle discovered in a tropical area of China.     

A bioremediation approach using natural transformation in pure-culture and mixed-population biofilms

Bacterial transformation by naked DNA is thought to contribute to gene transfer and microbial evolution within natural environments. In nature many microbial communities exist as complex assemblages known as biofilms where genetic exchange is facilitated. It may be possible to take advantage of natural transformation processes to modify the phenotypes of biofilm communities giving them specific and desirable functions. Work described here shows that biofilms composed of either pure cultures or mixed populations can be transformed with specific catabolic genes such that the communities acquire the ability to degrade a particular xenobiotic compound. Biofilms were transformed by plasmids bearing genes encoding green fluorescent protein (mut2) and/or atrazine chlorohydrolase (atzA). Confocal microscopy was used to quantify the number of transformants expressing mut2 in the biofilms. Degradation of atrazine by expressed atzA was quantified by tandem mass spectrometry. PCR analysis was performed to confirm the presence of atzA in transformed biofilms. These results indicate that it should be possible to use natural transformation to enhance bioremediation processes performed by biofilms.     

Actividad de la micafungina contra las biopelículas de Candida

BackgroundMost recalcitrant infections are associated to colonization and microbial biofilm development. These biofilms are difficult to eliminate by the immune response mechanisms and the current antimicrobial therapy.AimTo describe the antifungal of micafungin against fungal biofilms based in the scientific and medical literature of recent years.MethodsWe have done a bibliographic retrieval using the scientific terms “micafungin”, “activity”, “biofilm”, “Candida”, “Aspergillus”, “fungi”, “mycos”*, susceptibility, in PubMed/Medline from the National Library of Medicine from 2006 to 2009.ResultsMost current antifungal agents (amphotericin B and fluconazole) and the new azole antifungals have no activity against fungal biofilms. However, micafungin and the rest of echinocandins are very active against Candida albicans, Candida dubliniensis, Candida glabrata, and Candida krusei biofilms but their activities are variable and less strong against Candida tropicalis and Candida parapsilosis biofilms. Moreover, they have not activities against the biofilms of Cryptococcus y Trichosporon.ConclusionsThe activity of micafungin against Candida biofilms gives more strength to its therapeutic indication for candidaemia and invasive candidiasis associated to catheter, prosthesis and other biomedical devices.     

Geomicrobiological Study of the Grotta dei Cervi,Porto Badisco,Italy

Speleothems (active stalactites, wall concretions), rock walls, ceiling, and soils from the galleries of Grotta dei Cervi, Porto Badisco, Italy, were sampled to investigate the culturable heterotrophic microbial communities present in this cave. Sampling was carried out in a transect of about 230 m from the entrance to the central gallery where numerous Gram-positive bacteria were isolated from all studied sites. Members of the genera Agromyces, Arthrobacter, Rhodococcus , and particularly Streptomyces , of the order Actinomycetales, are spread throughout the whole cave. The ability of actinomycetes, and particularly of Nocardiopsis , to colonize salt-stressed environments is favored by the presence of ectoine, a compatible solute for osmotic adaptation. Selected actinomycete isolates were tested for the formation of crystals. Strains from all tested genera, except isolates of Gordonia and Nocardia , produced vaterite and/or calcite. Production of Mgcalcite was restricted to strains of Brachybacterium, Rhodococcus , and Streptomyces , whereas struvite was only precipitated by an unidentified isolate. These findings indicate that actinomycetes may play a role in the formation of mineral deposits in caves.     

Acidic Cave-Wall Biofilms Located in the Frasassi Gorge,Italy

Acidic biofilms present on cave walls in the sulfidic region of the Frasassi Gorge, Italy, were investigated to determine their microbial composition and their potential role in cave formation and ecosystem functioning. All biofilm samples examined had pH values &lt; 1.0. Scanning electron microscopy of the biofilms revealed the presence of various filaments and rods associated in large clusters with mineral crystals. Qualitative energy-dispersive x-ray analysis was used to determine that the crystals present on the cave walls, associated with the microbial biofilm, were composed of calcium and barium sulfate. Ribosomal RNA-based methods to determine the microbial composition of these biofilms revealed the presence of at least two strains of potential acidophilic, sulfur-oxidizing bacteria, belonging to the genera Thiobacillus and Sulfobacillus. An acid-producing strain of Thiobacillus sp. also was obtained in pure culture. Stable isotope ratio analysis of carbon and nitrogen showed that the wall biofilms are isotopically light, suggesting that in situ chemoautotrophic activity plays an important role in this subsurface ecosystem.     

Distribution and phylogenetic relationships of Australian glow-worms Arachnocampa (Diptera, Keroplatidae)

Glow-worms are bioluminescent fly larvae (Order Diptera, genus Arachnocampa) found only in Australia and New Zealand. Their core habitat is rainforest gullies and wet caves. Eight species are present in Australia; five of them have been recently described. The geographic distribution of species in Australia encompasses the montane regions of the eastern Australian coastline from the Wet Tropics region of northern Queensland to the cool temperate and montane rainforests of southern Australia and Tasmania. Phylogenetic trees based upon partial sequences of the mitochondrial genes cytochrome oxidase II and 16S mtDNA show that populations tend to be clustered into allopatric geographic groups showing overall concordance with the known species distributions. The deepest division is between the cool-adapted southern subgenus, Lucifera, and the more widespread subgenus, Campara. Lucifera comprises the sister groups, A. tasmaniensis, from Tasmania and the newly described species, A. buffaloensis, found in a high-altitude cave at Mt Buffalo in the Australian Alps in Victoria. The remaining Australian glow-worms in subgenus Campara are distributed in a swathe of geographic clusters that extend from the Wet Tropics in northern Queensland to the temperate forests of southern Victoria. Samples from caves and rainforests within any one geographic location tended to cluster together within a clade. We suggest that the morphological differences between hypogean (cave) and epigean (surface) glow-worm larvae are facultative adaptations to local microclimatic conditions rather than due to the presence of cryptic species in caves.     

Environmental pH modulates biofilm formation and matrix composition in Candida albicans and Candida glabrata

Abstract

Candida species are fungal opportunistic pathogens capable of colonizing and infecting various human anatomical sites, where they have to adapt to distinct niche-specific pH conditions. The aim of this study was to analyse the features of Candida albicans and Candida glabrata biofilms developed under neutral and vaginal acidic (pH 4) conditions. C. albicans produced thicker and more filamentous biofilms under neutral than under acidic conditions. On the other hand, the formation of biofilms by C. glabrata was potentiated by the acidic conditions suggesting the high adaptability of this species to the vaginal environment. In general, both species developed biofilms containing higher amounts of matrix components (protein and carbohydrate) under neutral than acidic conditions, although the opposite result was found for one C. glabrata strain. Overall, this study contributes to a better understanding of the modulation of C. albicans and C. glabrata virulence by specific pH conditions.     

Levels of selection in biofilms: multispecies biofilms are <Emphasis Type="Italic">not</Emphasis> evolutionary individuals

Microbes are generally thought of as unicellular organisms, but we know that many microbes live as parts of biofilms—complex, surface-attached microbial communities numbering millions of cells. Some authors have recently argued in favour of reconceiving biofilms as biological entities in their own right. In particular, some have claimed that multispecies biofilms are evolutionary individuals (Doolittle in Biol Philos 28:351–378, 2013; Ereshefsky and Pedroso in PNAS USA 112(33): 10126–10132 2015). Against this view, I defend the conservative consensus that selection acts primarily upon microbial cells.     

Primary faunal succession in volcanic terrain: lava and cave studies on the Canary Islands

Invertebrate communities in volcanic habitats of different ages on the islands of La Palma and El Hierro were studied using standardized trapping and searching techniques. A variety of graphical and numerical approaches were used to analyse relationships among the sites. Young, barren lava flows constitute aeolian ecosystems with a fauna of generalized detritivores and predators, especially collembolans, earwigs, thysamirans and crickets. Surface samples have many individuals and low diversity; those from caves have smaller numbers but similar taxonomic composition.
Vegetated surface habitats have richer communities, with diverse herbivores and predators but largely without the pioneer 'lavicolous' species. Caves with high humidity and stable temperature contain mainly specialized troglobitic species, but if there are both dry and humid sections lavicoles may also be present. Divergence into distinct epigean and hypogean communities results from both abiotic and biotic processes, including erosion and plant succession. While these occur mainly on the surface they also affect caves, increasing humidity and providing insulation from variations in external environmental conditions; the process is considered as a form of 'maturation' of the caves. Various models of succession are considered, which might help to account for the disappearance of lavicoles from mature epigean and hypogean communities.     

Morphometry and composition of aragonite and vaterite otoliths of deformed laboratory reared juvenile herring from two populations

Vaterite otoliths were sampled from two reared populations (Celtic and Clyde Seas) of juvenile herring Clupea harengus. The crystallography, elemental composition and morphometry were analysed and compared with those of normal aragonite otoliths. The incidence of vaterite otoliths in the juveniles sampled (n = 601) ranged from 7·8% in the Clyde population to 13·9% in the Celtic Sea population, and was 5·5% in the small sample (n = 36) of wild adults examined. In all but one case fish had only one vaterite otolith; the corresponding otolith of the pair was completely aragonite. Although the majority of the juveniles sampled showed craniofacial deformities, there was no link between the skull or jaw malformation and the incidence of vaterite otoliths. All vaterite otoliths had an aragonite inner area, and vaterite deposition began sometime after the age of 90 days. The vaterite otoliths were larger and lighter than their corresponding aragonite partners, and were less dense as a consequence of the vaterite crystal structure. The vaterite areas of the otoliths were depleted in Sr, Na and K. Concentrations of Mn were higher in the vaterite areas. The transition between the aragonite inner areas and the vaterite areas was sharply delineated. Within a small spatial scale (20 μm³) in the vaterite areas, however, there was co‐precipitation of both vaterite and aragonite. The composition of the aragonite cores in the vaterite otoliths was the same as in the cores of the normal aragonite otoliths indicating that the composition of the aragonite cores did not seed the shift to vaterite. Vaterite is less dense than aragonite, yet the concentrations of Ca analysed with wavelength‐dispersive spectrometry (WDS) were the same between the two polymorphs, indicating that Ca concentrations measured with WDS are not a good indicator of hypermineralized zones with high mineral density. The asymmetry in density and size of the otoliths may cause disruptions of hearing and pressure sensitivity for individual fish with one vaterite otolith, however, the presence of vaterite otoliths did not seem to affect the growth of these laboratory reared juvenile herring.     

Microbially Influenced Corrosion as a Model System for the Study of Metal Microbe Interactions: A Unifying Electron Transfer Hypothesis

The general term biomineralisation refers to biologically induced mineralisation in which an organism modifies its local microenvironment creating conditions such that there is chemical precipitation of mineral phases extracellularly. Most usually this results from an oxidation or reduction carried out by some microbial species, with the formation of a recognised biomineralised product. These reactions play a major role in microbial physiology and ecology, and are of central importance to such engineering consequences as microbial mining and microbially influenced corrosion. This paper will examine metal microbe interactions, both in naturally occurring microbial ecosystems and in two particular cases of biocorrosion, with the objective of putting forward a unifying hypothesis relevant to the understanding of each of these apparently disparate processes.