In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80°C that are white or yellow from precipitated sulfur (sulfur mats). In low-sulfide hot springs in the same area, grey or pink streamers are formed at 80 to 90°C, and a Chloroflexus mat is formed at 65 to 70°C. We have studied the microbial diversity of one sulfur mat (high-sulfide) hot spring and one Chloroflexus mat (low-sulfide) hot spring by cloning and sequencing of small-subunit rRNA genes obtained by PCR amplification from mat DNA. Using 98% sequence identity as a cutoff value, a total of 14 bacterial operational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the sulfur mat; 18 bacterial OTUs were detected in the Chloroflexus mat. Although representatives of novel divisions were found, the majority of the sequences were >95% related to currently known sequences. The molecular diversity analysis showed that Chloroflexus was the dominant mat organism in the low-sulfide spring (1 mg liter ؊1 ) below 70°C, whereas Aquificales were dominant in the high-sulfide spring (12 mg liter ؊1 ) at the same temperature. Comparison of the present data to published data indicated that there is a relationship between mat type and composition of Aquificales on the one hand and temperature and sulfide concentration on the other hand.Sulfide-rich hot springs with neutral or alkaline pH are relatively rare in most geothermal areas in the world. However, these types of hot springs are rather common in Iceland due to high ground water level and climatic conditions, i.e., from melting snow and rain. Bacteria that thrive in such springs often form long streamers or mats, but the appearance of the mats and the types of bacteria in them seem to vary depending on the sulfide concentration, pH, temperature, and other chemical and physical factors (6,7,10,11,12,20,33). Many Icelandic hot springs have sulfide concentrations as high as 30 mg liter Ϫ1 and, under such conditions, thick bacterial mats which can be spectacularly white or bright yellow from precipitated sulfur are formed.The diversity of many microbial ecosystems has now been studied with different molecular methods, such as analysis of small-subunit (SSU) rRNA by sequencing, denaturing gradient gel electrophoresis, or restriction fragment length polymorphism analyses. These studies show that the diversity of microbial ecosystems is typically 100 to 1,000 times greater than that shown by cultivation alone (14,15,22,23,30,31). The sequencing of rRNA genes from environmental samples is very informative, since it provides information on both the phylogenetic relationship and the population structure of the microbial community. With increased understanding of the role and importance of microbes in many ecosystems, the benefit of microbial diversity studies is being recognized. The practical value of these methods is already widespread, as they can be used to study the performance of wastewater treatment plants (27), monitor changes upo...

With the submersible JAGO and by scuba diving we discovered three remarkable geothermal cones, rising 33, 25, and 45 m from the seafloor at a depth of 65 m in Eyjafjordur, northern Iceland. The greatest geothermal activity was on the highest cone, which discharged up to 50 liters of freshwater per s at 72°C and pH 10.0. The cones were built up from precipitated smectite, formed by mixing of the hot SiO 2 -rich geothermal fluid with the cold Mg-rich seawater. By connecting a rubber hose to one outflow, about 240 liters of pure geothermal fluids was concentrated through a 0.2-m-pore-size filter. Among 50 thermophilic isolates, we found members of Bacillus and Thermonema and a new unidentified low-G؉C gram-positive member of the Bacteria as well as one member of the Archaea, Desulfurococcus mobilis. Analysis of small-subunit rRNA genes PCR amplified and cloned directly from environmental DNA showed that 41 out of 45 Bacteria sequences belonged to members of the Aquificales, whereas all of the 10 Archaea sequences belonged to the Korarchaeota. The physiological characteristics of isolates from different parts of the cones indicate a completely freshwater habitat, supporting the possibility of subterranean transmittance of terrestrial organisms.Since the discovery of hydrothermal activity on oceanic spreading centers in the Eastern Pacific in 1977 and 1979, hot springs have been found at numerous locations on ridge systems (7, 24). The Mid-Atlantic ridge is one of these systems, and Iceland, with its volcanic activity, is the only place where it emerges from the sea. The Eyjafjordur region, in northern Iceland, is one of several localities in Iceland with known submarine geothermal activity. The geothermal activity is in basaltic lava 6 to 12 million years of age (5, 14) and seems to be related to either one or both of two NNE-and NW-trending fault zones with no known surface hot spring activity (4).Oceanic hydrothermal vent fluids originate from seawater, which percolates into the oceanic crust and is heated at the top of magma chambers or in hot rock formations. The hot fluid, discharged from the seafloor, is anoxic and acidic, with salinity varying from 0.1 to 2 times that of seawater and with variable chemical composition (29). Elements dissolved in the hydrothermal fluid precipitate around the vents, commonly forming characteristic chimney-like structures (6, 9). In such an extreme environment, diverse types of thermophilic microorganisms have been detected and isolated (21).Molecular phylogenetic studies on environmental DNA from hydrothermal vent samples have been limited due to low quantity and poor quality of the collected biomass. Part of the problem at submarine hot springs is that they are difficult to access and samples are therefore precious. A variety of sampling devices have been used to collect hydrothermal vent samples for chemical and microbiological analysis. These include samplers for collecting hot fluid, for collecting particles from both warm and hot fluids, and for measuring in situ microbial...

Mesophilic, moderately halophilic bacteria were isolated from a silica-rich geothermal lake, the Blue Lagoon in Iceland. The isolates are strictly aerobic, but reduce nitrate to nitrite, and are oxidase- and catalase-positive. The nonsporeforming and nonmotile Gram negative rods are 0.6-0.8 microm in diameter and variable in length (9-18 microm), and contain gas vacuoles. The GC content in their DNA is 66.15%. The minimum, optimum, and maximum temperatures for growth are 22 degrees C, 45 degrees C, and 50 degrees C, respectively. The isolates do not grow without added salt in the medium and can grow at up to 7% NaCl (w/v). The optimal salinity for growth is 3.5%-4% NaCl. The pH range for growth is 6.5-8.5, with the optimal pH at 7.0. At optimal conditions the bacterium has a doubling time of 80 min. The main cytochrome is a membrane-bound cytochrome c with an alpha-peak at 549nm. Sequencing of 16S rRNA from the type strain ITI-1157 revealed it to be a proteobacterium of the alpha-subclass with the closest relatives being Roseobacter litoralis and Paracoccuss kocuri. The new isolates do not contain bacteriochlorophyll a and are considered to represent a new genus and a new species, Silicibacter lacuscaerulensis.

Rhodothermus marinus has been the subject of many studies in recent years. It is a thermohalophilic bacterium and is the only validly described species in the genus Rhodothermus. It is not closely related to other well-known thermophiles and is the only thermophile within the family Crenotrichaceae. R. marinus has been isolated from several similar but distantly located geothermal habitats, many of which are subject to large fluctuations in environmental conditions. This presumably affects the physiology of R. marinus. Many of its enzymes show optimum activity at temperatures considerably higher than 65 degrees C, the optimum for growth, and some are active over a broad temperature range. Studies have found distinguishing components in the R. marinus electron transport chain as well as in its pool of intracellular solutes, which accumulate during osmotic stress. The species hosts both bacteriophages and plasmids and a functional intein has been isolated from its chromosome. Despite these interesting features and its unknown genetics, interest in R. marinus has been mostly stimulated by its thermostable enzymes, particularly polysaccharide hydrolysing enzymes and enzymes of DNA synthesis which may be useful in industry and in the laboratory. R. marinus has not been amenable to genetic analysis until recently when a system for gene transfer was established. Here, we review the current literature on R. marinus.

Aims:  To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro. Methods and Results:  A bacterial mixture was added eight times to the rearing water from the prehatch to the mid‐larval stage (a 38‐day period). Microbiological analysis of ova, larvae and rearing water was performed regularly. Larval performance and development were evaluated by survival rate, hypersalinity tolerance and physiological measurements. Different larval survival rates were observed within and between treatments, and possibly explained by variations in larval microflora and established probionts. Larvae from one silo, which had been bathed in the bacterial suspension, showed the highest survival rate (42·1%), lowest Vibrio levels, and were significantly heavier (19·3%) and more stress tolerant than control larvae (P < 0·01). This coincided with the intestinal establishment of two of the tested bacteria. Conclusions:  Arthrobacter and Enterococcus strains added regularly to the rearing water from the postfertilized egg stage can become established in larval gastrointestinal tract. The Enterococcus strain was associated with increased larval growth, performance and microflora control, indicating its probiotic nature. Significance and Impact of the Study:  Regular application of autochthonous probionts may promote larval welfare, development and stress tolerance at early stages, hence increasing production yield in intensive cod larviculture.