Active transport and accumulation of iodide by newly isolated marine bacteria

Iodide (I(-))-accumulating bacteria were isolated from marine sediment by an autoradiographic method with radioactive (125)I(-). When they were grown in a liquid medium containing 0.1 microM iodide, 79 to 89% of the iodide was removed from the medium, and a corresponding amount of iodide was detected in the cells. Phylogenetic analysis based on 16S rRNA gene sequences indicated that iodide-accumulating bacteria were closely related to Flexibacter aggregans NBRC15975 and Arenibacter troitsensis, members of the family Flavobacteriaceae. When one of the strains, strain C-21, was cultured with 0.1 microM iodide, the maximum iodide content and the maximum concentration factor for iodide were 220 +/- 3.6 (mean +/- standard deviation) pmol of iodide per mg of dry cells and 5.5 x 10(3), respectively. In the presence of much higher concentrations of iodide (1 microM to 1 mM), increased iodide content but decreased concentration factor for iodide were observed. An iodide transport assay was carried out to monitor the uptake and accumulation of iodide in washed cell suspensions of iodide-accumulating bacteria. The uptake of iodide was observed only in the presence of glucose and showed substrate saturation kinetics, with an apparent affinity constant for transport and a maximum velocity of 0.073 muM and 0.55 pmol min(-1) mg of dry cells(-1), respectively. The other dominant species of iodine in terrestrial and marine environments, iodate (IO(3)(-)), was not transported.     

Superoxide Production by a Manganese-Oxidizing Bacterium Facilitates Iodide Oxidation

The release of radioactive iodine (i.e., iodine-129 and iodine-131) from nuclear reprocessing facilities is a potential threat to human health. The fate and transport of iodine are determined primarily by its redox status, but processes that affect iodine oxidation states in the environment are poorly characterized. Given the difficulty in removing electrons from iodide (I⁻), naturally occurring iodide oxidation processes require strong oxidants, such as Mn oxides or microbial enzymes. In this study, we examine iodide oxidation by a marine bacterium, Roseobacter sp. AzwK-3b, which promotes Mn(II) oxidation by catalyzing the production of extracellular superoxide (O₂⁻). In the absence of Mn²⁺, Roseobacter sp. AzwK-3b cultures oxidized ∼90% of the provided iodide (10 μM) within 6 days, whereas in the presence of Mn(II), iodide oxidation occurred only after Mn(IV) formation ceased. Iodide oxidation was not observed during incubations in spent medium or with whole cells under anaerobic conditions or following heat treatment (boiling). Furthermore, iodide oxidation was significantly inhibited in the presence of superoxide dismutase and diphenylene iodonium (a general inhibitor of NADH oxidoreductases). In contrast, the addition of exogenous NADH enhanced iodide oxidation. Taken together, the results indicate that iodide oxidation was mediated primarily by extracellular superoxide generated by Roseobacter sp. AzwK-3b and not by the Mn oxides formed by this organism. Considering that extracellular superoxide formation is a widespread phenomenon among marine and terrestrial bacteria, this could represent an important pathway for iodide oxidation in some environments.     

Radiotracer Experiments on Biological Volatilization of Organic Iodine from Coastal Seawaters

Biological volatilization of iodine from seawaters was studied using a radiotracer technique. Seawater samples were incubated aerobically in serum bottles with radioactive iodide tracer (¹²⁵I), and volatile organic and inorganic iodine were collected with activated charcoal and silver wool trap, respectively. Iodine was volatilized mainly as organic iodine, and inorganic iodine volatilization was not observed. Influence of light intensity on the volatilization was determined, but no significant differences were observed under light (70,000 lux) and dark conditions. The effect of the chemical form of iodine on the volatilization was determined, and the results suggested that volatilization preferentially occurs from iodide (I^?) but not from iodate (IO₃ ^?). Volatilization did not occur when the samples were autoclaved or filtered through a 0.22-μm pore size membrane filter. Incubation of the samples with antibiotics caused decreased volatilization. Conversely, enhanced volatilization was observed when the samples were incubated with yeast extract. Fifty-nine marine bacterial strains were then randomly isolated from marine environments, and their iodine-volatilizing capacities were determined. Among these, 19 strains exhibited significant capacities for volatilizing iodine. 16S ribosomal RNA gene comparisons indicated that these bacteria are members of Proteobacteria (α and γ subdivisions) and Cytophaga-Flexibacter-Bacteroides group. One of the strains, strain C-19, volatilized 1 to 2% of total iodine during cultivation, and the gaseous organic iodine was identified as methyl iodide (CH₃I). These results suggest that organic iodine volatilization from seawaters occurs biologically, and that marine bacteria participate in the process. Considering that volatile organic iodine emitted from the oceans causes atmospheric ozone destruction, biological iodine volatilization from seawater is of great importance. Our results also contribute to prediction of movement and diffusion of long-lived radioactive iodine (¹²⁹I) in the environment.     

Active Transport and Accumulation of Iodide by Newly Isolated Marine Bacteria

Iodide (I⁻)-accumulating bacteria were isolated from marine sediment by an autoradiographic method with radioactive ¹²⁵I⁻. When they were grown in a liquid medium containing 0.1 μM iodide, 79 to 89% of the iodide was removed from the medium, and a corresponding amount of iodide was detected in the cells. Phylogenetic analysis based on 16S rRNA gene sequences indicated that iodide-accumulating bacteria were closely related to Flexibacter aggregans NBRC15975 and Arenibacter troitsensis, members of the family Flavobacteriaceae. When one of the strains, strain C-21, was cultured with 0.1 μM iodide, the maximum iodide content and the maximum concentration factor for iodide were 220 ± 3.6 (mean ± standard deviation) pmol of iodide per mg of dry cells and 5.5 × 10³, respectively. In the presence of much higher concentrations of iodide (1 μM to 1 mM), increased iodide content but decreased concentration factor for iodide were observed. An iodide transport assay was carried out to monitor the uptake and accumulation of iodide in washed cell suspensions of iodide-accumulating bacteria. The uptake of iodide was observed only in the presence of glucose and showed substrate saturation kinetics, with an apparent affinity constant for transport and a maximum velocity of 0.073 μM and 0.55 pmol min⁻¹ mg of dry cells⁻¹, respectively. The other dominant species of iodine in terrestrial and marine environments, iodate (IO₃⁻), was not transported.     

Nutrient speciation and hydrography in two anchialine caves in Croatia: tools to understand iodine speciation

Despite iodine being one of the most abundant of the minor elements in oxic seawater, the principal processes controlling its interconversion from iodate to iodide and vice versa, are still either elusive or largely unknown. The two major hypotheses for iodate reduction involve either phytoplankton growth in primary production, or bacteria during regeneration. An earlier study intended to exploit the unusual nature of anchialine environments revealed that iodide is oxidised to iodate in the bottom of such caves, whereas reduction of iodate occurs in the shallower parts of the water column. This investigation was made on the hypothesis that study of the nitrogen and phosphorus nutrient systems within the caves might offer a bridge between the iodine chemistry and the marine bacteria which are assumed to be the agent of change of the iodine in the caves. Accordingly, the hydrography, the nutrient chemistry, and some further iodine studies were made of two anchialine caves on the east coast of the Adriatic Sea in Croatia. Iodate and iodide were determined by differential pulse voltammetry and cathodic stripping square-wave voltammetry, respectively. Total iodine was determined indirectly, as iodate, after oxidation of reduced iodine species with UV irradiation and strong chemical oxidants. Nutrient concentrations were measured by spectrophotometry. Nutrient profiles within the well stratified water columns indicate a relatively short-lived surface source of nitrate and phosphate to the caves, with a more conventional, mid-water, nutrient regeneration system. The latter involves nitrite and ammonium at the bottom of the halocline, suggestive of both autotrophic and heterotrophic microbial activity. High iodate/low iodide deep water, and conservative behaviour of total inorganic iodine were confirmed in both systems. Iodate is reduced to iodide in the hypoxic region where nutrient regeneration occurs. The concentrations of organic iodine were surprisingly high in both systems, generally increasing toward the surface, where it comprised almost 80% of total iodine. As with alkalinity and silica, the results suggest that this refractive iodine component is liberated during dissolution of the surrounding karst rock. A major, natural flushing of one of the caves with fresh water was confirmed, showing that the cave systems offer the opportunity to re-start investigations periodically.     

Analytical Studies of Iodine in Food Substances

Four species of edible brown marine algae were fractionated by trichloroacetic acid precipitation and subsequent chromatography; and the iodine content of each fraction was determined. Quantitative determination of iodide form iodine was made possible by elimination of interfereing substances in cell extract using a weakly basic anion exchange resin column without drastic procedure.

Although the iodine content of each algae was of much diversity owing to species, the iodide form iodine varied between 83~85% of total iodine independent on total iodine content. The rest of the iodine was mostly found in trichloroacetic acid precipitate probably in protein bound form; and each algae contained little trichloroacetic acid soluble non iodide form of iodine, probably a low molecular organic form iodine.     

Production of free and organic iodine by Roseovarius spp

Two strains of iodine-producing bacteria were isolated from marine samples. 16S rRNA gene sequences indicated the strains were most closely related to Roseovarius tolerans, and phylogenetic analysis indicated both belong to the same genus. 5 mM iodide inhibited the growth of strain 2S5-2 almost completely, and of strain S6V slightly. Both strains produced free iodine and organic iodine from iodide. CH2I2, CHI3 and CH2ClI were the main organic iodines produced by strain 2S5-2, and CHI3 and CH2I2 by strain S6V. Experiments using cells and spent media suggested that the organic iodines were produced from the compounds released or contained in the media and cells were necessary for the considerable production of CH2I2 and CH2ClI, though CHI3 was produced by spent media with H2O2 or free iodine.     

Hydrogen Peroxide-Dependent Uptake of Iodine by Marine Flavobacteriaceae Bacterium Strain C-21

The cells of the marine bacterium strain C-21, which is phylogenetically closely related to Arenibacter troitsensis, accumulate iodine in the presence of glucose and iodide (I⁻). In this study, the detailed mechanism of iodine uptake by C-21 was determined using a radioactive iodide tracer, ¹²⁵I⁻. In addition to glucose, oxygen and calcium ions were also required for the uptake of iodine. The uptake was not inhibited or was only partially inhibited by various metabolic inhibitors, whereas reducing agents and catalase strongly inhibited the uptake. When exogenous glucose oxidase was added to the cell suspension, enhanced uptake of iodine was observed. The uptake occurred even in the absence of glucose and oxygen if hydrogen peroxide was added to the cell suspension. Significant activity of glucose oxidase was found in the crude extracts of C-21, and it was located mainly in the membrane fraction. These findings indicate that hydrogen peroxide produced by glucose oxidase plays a key role in the uptake of iodine. Furthermore, enzymatic oxidation of iodide strongly stimulated iodine uptake in the absence of glucose. Based on these results, the mechanism was considered to consist of oxidation of iodide to hypoiodous acid by hydrogen peroxide, followed by passive translocation of this uncharged iodine species across the cell membrane. Interestingly, such a mechanism of iodine uptake is similar to that observed in iodine-accumulating marine algae.     

A newly discovered oxidant defence system and its involvement in the development of Aurelia aurita (Scyphozoa, Cnidaria): reactive oxygen species and elemental iodine control medusa formation

In Aurelia aurita, applied iodine induces medusa formation (strobilation). This process also occurs when the temperature is lowered. This was found to increase oxidative stress resulting in an increased production of iodine from iodide. One polyp produces several medusae (initially termed ephyrae) starting at the polyp's oral end. The spreading of strobilation down the body column is controlled by a feedback loop: ephyra anlagen decrease the tyrosine content in adjacent polyp tissue by producing melanin from tyrosine. Endogenous tyrosine is able to remove iodine by forming iodiferous tyrosine compounds. The reduced level of tyrosine causes the ephyra-polyp-border to move towards the basal end of the former polyp. We argue that an oxidant defence system may exist which makes use of iodide and tyrosine. Like other marine invertebrates, polyps of Aurelia contain iodide ions. Inevitably produced peroxides oxidise iodide into iodine. The danger to be harmed by iodine is strongly decreased by endogenous tyrosine which reacts with iodine to form iodiferous tyrosine compounds including thyroxin. Both substances together, iodide and tyrosine, form an efficient oxidant defence system which shields the tissue against damage by reactive oxygen species. In the course of evolution (from a species at the basis of the animal kingdom like Aurelia to a highly evolved species like man) the waste product thyroxin (indicating a high metabolic rate) has developed into a hormone which controls the metabolic rate.     

黄海海域海洋沉积物细菌多样性分析

【背景】海洋独特的环境造就了海洋生物的多样性,海洋沉积物中细菌对海洋环境具有至关重要的作用。【目的】研究陆地土壤和海洋沉积物间细菌群落相似性和差异性,以便更好地认识海洋细菌多样性,深入了解沉积物细菌在海洋环境中的潜在作用。【方法】从中国黄海海域及大连市大黑山脚下分别采集样品,以陆地土壤为对照,采用16SrRNA基因高通量测序技术分析海洋沉积物的细菌群落结构。【结果】海洋沉积物样品中芽孢杆菌纲(Bacilli)、鞘氨醇单胞菌属(Sphingomonas)和芽孢杆菌属(Bacillus)丰度高于陆地土壤样品;海洋沉积物中亚硝化单胞菌(unculturedbacterium f. Nitrosomonadaceae)和厌氧绳菌(uncultured bacterium f. Anaerolineaceae)丰度虽低于陆地土壤,但丰度值也均高于1%;样品分类学统计显示酸杆菌门(Acidobacteria)在海洋沉积物和陆地土壤样品中的序列丰度比例都较大,鞘氨醇单胞菌属(Sphingomonas)在海洋沉积物样品中的序列丰度大于陆地土壤样品。【结论】海洋沉积物细菌多样性可作为海洋环境恢复情况的重要指标,研究为合理开发和利用海洋资源提供理论依据。     

Uptake of iodide in the marine haptophyte Isochrysis sp. (T.ISO) driven by iodide oxidation

Uptake of iodide was studied in the marine microalga Isochrysis sp. (isol. Haines, T.ISO) during short‐term incubations with radioactive iodide (¹²⁵I^?). Typical inhibitors of the sodium/iodide symporter (NIS) did not inhibit iodide uptake, suggesting that iodide is not taken up through this transport protein, as is the case in most vertebrate animals. Oxidation of iodide was found to be an essential step for its uptake by T.ISO and it seemed likely that hypoiodous acid (HOI) was the form of iodine taken up. Uptake of iodide was inhibited by the addition of thiourea and of other reducing agents, like L‐ascorbic acid, L‐glutathione and L‐cysteine and increased after the addition of oxidized forms of the transition metals Fe and Mn. The simultaneous addition of both hydrogen peroxide (H₂O₂) and a known iodide‐oxidizing myeloperoxidase (MPO) significantly increased iodine uptake, but the addition of H₂O₂ or MPO separately, had no effect on uptake. This confirms the observation that iodide is oxidized prior to uptake, but it puts into doubt the involvement of H₂O₂ excretion and membrane‐bound or extracellular haloperoxidase activity of T.ISO. The increase of iodide uptake by T.ISO upon Fe(III) addition suggests the nonenzymatic oxidation of iodide by Fe(III) in a redox reaction and subsequent influx of HOI. This is the first report on the mechanism of iodide uptake in a marine microalga.     

Iodide accumulation by aerobic bacteria isolated from subsurface sediments of a 129I-contaminated aquifer at the Savannah River site, South Carolina

(129)I is of major concern because of its mobility in the environment, excessive inventory, toxicity (it accumulates in the thyroid), and long half-life (～16 million years). The aim of this study was to determine if bacteria from a (129)I-contaminated oxic aquifer at the F area of the U.S. Department of Energy's Savannah River Site, SC, could accumulate iodide at environmentally relevant concentrations (0.1 μM I(-)). Iodide accumulation capability was found in 3 out of 136 aerobic bacterial strains isolated from the F area that were closely related to Streptomyces/Kitasatospora spp., Bacillus mycoides, and Ralstonia/Cupriavidus spp. Two previously described iodide-accumulating marine strains, a Flexibacter aggregans strain and an Arenibacter troitsensis strain, accumulated 2 to 50% total iodide (0.1 μM), whereas the F-area strains accumulated just 0.2 to 2.0%. Iodide accumulation by FA-30 was stimulated by the addition of H(2)O(2), was not inhibited by chloride ions (27 mM), did not exhibit substrate saturation kinetics with regard to I(-) concentration (up to 10 μM I(-)), and increased at pH values of <6. Overall, the data indicate that I(-) accumulation likely results from electrophilic substitution of cellular organic molecules. This study demonstrates that readily culturable, aerobic bacteria of the F-area aquifer do not accumulate significant amounts of iodide; however, this mechanism may contribute to the long-term fate and transport of (129)I and to the biogeochemical cycling of iodine over geologic time.     

Marine Bacteroidetes enzymatically digest xylans from terrestrial plants

Marine Bacteroidetes that degrade polysaccharides contribute to carbon cycling in the ocean. Organic matter, including glycans from terrestrial plants, might enter the oceans through rivers. Whether marine bacteria degrade structurally related glycans from diverse sources including terrestrial plants and marine algae was previously unknown. We show that the marine bacterium Flavimarina sp. Hel_I_48 encodes two polysaccharide utilization loci (PULs) which degrade xylans from terrestrial plants and marine algae. Biochemical experiments revealed activity and specificity of the encoded xylanases and associated enzymes of these PULs. Proteomics indicated that these genomic regions respond to glucuronoxylans and arabinoxylans. Substrate specificities of key enzymes suggest dedicated metabolic pathways for xylan utilization. Some of the xylanases were active on different xylans with the conserved β-1,4-linked xylose main chain. Enzyme activity was consistent with growth curves showing Flavimarina sp. Hel_I_48 uses structurally different xylans. The observed abundance of related xylan-degrading enzyme repertoires in genomes of other marine Bacteroidetes indicates similar activities are common in the ocean. The here presented data show that certain marine bacteria are genetically and biochemically variable enough to access parts of structurally diverse xylans from terrestrial plants as well as from marine algal sources.     

Direct Acridine Orange Counting of Bacteria Preserved with Acidified Lugol Iodine

Acidified and nonacidified Lugol iodine solution was tested under several storage temperatures and at several times as a preservative for marine bacteria. Direct counts with acridine orange showed no significant difference between glutaraldehyde- and Lugol iodine solution-preserved samples under any storage temperature when samples were counted within 1 week of collection. Specimens in long-term (up to 6 months) storage required refrigeration and treatment with acidified Lugol iodine solution for adequate preservation. Lugol iodine solution-preserved bacteria appeared intact under scanning electron microscopy. Lugol iodine solution did not preserve chlorophyll autofluorescence in phytoplankton.     

Marine bacterial diversity as a resource for novel microbial products

Marine bacteria are an important and relatively unexplored resource for novel microbial products. In this review, we discuss a number of issues relevant to the industrial potential of marine microorganisms including how marine and terrestrial bacteria differ, both physiologically and taxonomically, and what constitute reasonable expectations of the biosynthetic capabilities of marine bacteria relative to terrestrial bacteria and to marine macroorganisms. Also discussed is the concept that bacterial associations with marine plants and animals, which range from casual encounters to obligate symbioses, provide unique opportunities for bacterial adaptation. It is proposed that some of these adaptations would not be selected for in the absence of environmental parameters associated with the host, and that these adaptations can include the biosynthesis of unique metabolic products.     

Isolation of Iodide-Oxidizing Bacteria from Iodide-Rich Natural Gas Brines and Seawaters

Iodide-oxidizing bacteria (IOB), which oxidize iodide (I⁻) to molecular iodine (I₂), were isolated from iodide-rich (63 μM to 1.2 mM) natural gas brine waters collected from several locations. Agar media containing iodide and starch were prepared, and brine waters were spread directly on the media. The IOB, which appeared as purple colonies, were obtained from 28 of the 44 brine waters. The population sizes of IOB in the brines were 10² to 10⁵ colony-forming units (CFU) mL⁻¹. However, IOB were not detected in natural seawaters and terrestrial soils (fewer than 10 CFU mL⁻¹ and 10² CFU g wet weight of soils⁻¹, respectively). Interestingly, after the enrichment with 1 mM iodide, IOB were found in 6 of the 8 seawaters with population sizes of 10³ to 10⁵ CFU mL⁻¹. 16S rDNA sequencing and phylogenetic analyses showed that the IOB strains are divided into two groups within the α-subclass of the Proteobacteria. One of the groups was phylogenetically most closely related to Roseovarius tolerans with sequence similarities between 94% and 98%. The other group was most closely related to Rhodothalassium salexigens, although the sequence similarities were relatively low (89% to 91%). The iodide-oxidizing reaction by IOB was mediated by an extracellular enzyme protein that requires oxygen. Radiotracer experiments showed that IOB produce not only I₂ but also volatile organic iodine, which were identified as diiodomethane (CH₂I₂) and chloroiodomethane (CH₂ClI). These results indicate that at least two types of IOB are distributed in the environment, and that they are preferentially isolated in environments in which iodide levels are very high. It is possible that IOB oxidize iodide in the natural environment, and they could significantly contribute to the biogeochemical cycling of iodine.     

Availability of iodide and iodate to spinach (Spinacia oleracea L.) in relation to total iodine in soil solution

A greenhouse pot experiment was carried out to investigate the availability of iodide and iodate to soil-grown spinach (Spinacia oleracea L.) in relation to total iodine concentration in soil solution. Four iodine concentrations (0, 0.5, 1, 2 mg kg⁻¹) for iodide (I⁻) and iodate (IO₃⁻) were used. Results showed that the biomass productions of spinach were not significantly affected by the addition of iodate and iodide to the soil, and that iodine concentrations in spinach plants on the basis of fresh weights increased with increasing addition of iodine. Iodine concentrations in tissues were much greater for plants grown with iodate than with iodide. In contrast to the iodide treatments, in iodate treatment leaves accounted for a larger fraction of the total plant iodine. The soil-to-leaf transfer factors (TF_leaf) for plants grown with iodate were about tenfold higher than those grown with iodide. Iodine concentrations in soil solution increased with increasing iodine additions to the soil irrespective of iodine species. However, total iodine in soil solution was generally higher for iodate treatments than iodide both in pots with and without spinach. According to these results, iodate can be considered as potential iodine fertilizer to increase iodine content in vegetables.     

The Gut Bacterial Community of Mammals from Marine and Terrestrial Habitats

After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.     

Bacterial symbionts in the hepatopancreas of isopods: diversity and environmental transmission

The midgut glands (hepatopancreas) of terrestrial isopods contain bacterial symbionts. We analysed the phylogenetic diversity of hepatopancreatic bacteria in isopod species from various suborders colonizing marine, semiterrestrial, terrestrial and freshwater habitats. Hepatopancreatic bacteria were absent in the marine isopod Idotea balthica (Valvifera). The symbiotic bacteria present in the midgut glands of the freshwater isopod Asellus aquaticus (Asellota) were closely related to members of the proteobacterial genera Rhodobacter, Burkholderia, Aeromonas or Rickettsiella, but differed markedly between populations. By contrast, species of the suborder Oniscidea were consistently colonized by the same phylotypes of hepatopancreatic bacteria. While symbionts in the semiterrestrial isopod Ligia oceanica (Oniscidea) were close relatives of Pseudomonas sp. (Gammaproteobacteria), individuals of the terrestrial isopod Oniscus asellus (Oniscidea) harboured either 'Candidatus Hepatoplasma crinochetorum' (Mollicutes) or 'Candidatus Hepatincola porcellionum' (Rickettsiales), previously described as symbionts of another terrestrial isopod, Porcellio scaber. These two uncultivated bacterial taxa were consistently present in each population of six and three different species of terrestrial isopods, respectively, collected in different geographical locations. However, infection rates of individuals within a population ranged between 10% and 100%, rendering vertical transmission unlikely. Rather, feeding experiments suggest that 'Candidatus Hepatoplasma crinochetorum' is environmentally transmitted to the progeny.     

Distribution of thermophilic endospores in a temperate estuary indicate that dispersal history structures sediment microbial communities

Endospores of thermophilic bacteria are found in cold and temperate sediments where they persist in a dormant state. As inactive endospores that cannot grow at the low ambient temperatures, they are akin to tracer particles in cold sediments, unaffected by factors normally governing microbial biogeography (e.g., selection, drift, mutation). This makes thermophilic endospores ideal model organisms for studying microbial biogeography since their spatial distribution can be directly related to their dispersal history. To assess dispersal histories of estuarine bacteria, thermophilic endospores were enriched from sediments along a freshwater‐to‐marine transect of the River Tyne in high temperature incubations (50°C). Dispersal histories for 75 different taxa indicated that the majority of estuarine endospores were of terrestrial origin; most closely related to bacteria from warm habitats associated with industrial activity. A subset of the taxa detected were marine derived, with close relatives from hot deep marine biosphere habitats. These patterns are consistent with the sources of sediment in the River Tyne being predominantly terrestrial in origin. The results point to microbial communities in estuarine and marine sediments being structured by bi‐directional currents, terrestrial run‐off and industrial effluent as vectors of passive dispersal and immigration.