Recent progress in the use of purple non-sulfur bacteria as probiotics in aquaculture.

The use of probiotics in aquaculture is widely recognized as an ecological and cost-effective approach to raising healthy, pathogen-tolerant aquatic animals, including fish and shrimp. In particular for shrimp, probiotics are viewed as a promising countermeasure to the recent severe damage to the shrimp industry by bacterial and viral pathogens. Purple non-sulfur bacteria (PNSB) are Gram-negative, non-pathogenic bacteria with wide application potential in agriculture, wastewater treatment, and bioenergy/biomaterials production. In aquaculture, lactic bacteria and Bacillus are the major probiotic bacteria used, but PNSB, like Rhodopseudomonas and Rhodobacter, are also used. In this review, we summarize the previous work on the use of PNSB in aquaculture, overview the previous studies on the stimulation of innate immunity of shrimp by various probiotic microorganisms, and also share our results in the probiotic performance of Rhodovulum sulfidophilum KKMI01, a marine PNSB, which showed a superior effect in promotion of growth and stimulation of immunity in shrimp at a quite low concentration of 1 × 103 cfu (colony forming unit)/ml in rearing water.

Geometry Effects on Light-Harvesting Complex's Light Absorption and Energy Transfer in Purple Bacteria.

Light-harvesting complexes (LHC) in photosynthetic organisms perform the major function of light absorption and energy transportation. Optical spectrum of LHC provides a detailed understanding of the molecular mechanisms involved in the excitation energy transfer (EET) processes, which has been widely studied. Here, we study how the geometric property of LHC in Rhodospirillum (Rs.) molischianum would affect its spectral characteristics and energy transfer process. By adopting the effective Hamiltonian and the dipole-dipole approximation, we calculate the exciton level structures for the LH2 ring and LH1 ring and the energy transfer time between different LHCs under various structural parameters and different rotational symmetries. Our numerical results show that the LHC's absorption peaks and the energy transfer time between different LHCs can be modified by changing the geometric configurations. Our study may be beneficial to the applications in designing highly efficient photovoltaic cell and other artificial photosynthetic systems.

Chemosynthetic symbiont with a drastically reduced genome serves as primary energy storage in the marine flatworm Paracatenula.

Hosts of chemoautotrophic bacteria typically have much higher biomass than their symbionts and consume symbiont cells for nutrition. In contrast to this, chemoautotrophic Candidatus Riegeria symbionts in mouthless Paracatenula flatworms comprise up to half of the biomass of the consortium. Each species of Paracatenula harbors a specific Ca Riegeria, and the endosymbionts have been vertically transmitted for at least 500 million years. Such prolonged strict vertical transmission leads to streamlining of symbiont genomes, and the retained physiological capacities reveal the functions the symbionts provide to their hosts. Here, we studied a species of Paracatenula from Sant'Andrea, Elba, Italy, using genomics, gene expression, imaging analyses, as well as targeted and untargeted MS. We show that its symbiont, Ca R. santandreae has a drastically smaller genome (1.34 Mb) than the symbiont´s free-living relatives (4.29-4.97 Mb) but retains a versatile and energy-efficient metabolism. It encodes and expresses a complete intermediary carbon metabolism and enhanced carbon fixation through anaplerosis and accumulates massive intracellular inclusions such as sulfur, polyhydroxyalkanoates, and carbohydrates. Compared with symbiotic and free-living chemoautotrophs, Ca R. santandreae's versatility in energy storage is unparalleled in chemoautotrophs with such compact genomes. Transmission EM as well as host and symbiont expression data suggest that Ca R. santandreae largely provisions its host via outer-membrane vesicle secretion. With its high share of biomass in the symbiosis and large standing stocks of carbon and energy reserves, it has a unique role for bacterial symbionts-serving as the primary energy storage for its animal host.

Quantitative assessment of individual populations within polymicrobial biofilms.

Selecting appropriate tools providing reliable quantitative measures of individual populations in biofilms is critical as we now recognize their true polymicrobial and heterogeneous nature. Here, plate count, quantitative real-time polymerase chain reaction (q-PCR) and peptide nucleic acid probe-fluorescence in situ hybridization (PNA-FISH) were employed to quantitate cystic fibrosis multispecies biofilms. Growth of Pseudomonas aeruginosa, Inquilinus limosus and Dolosigranulum pigrum was assessed in dual- and triple-species consortia under oxygen and antibiotic stress. Quantification methods, that were previously optimized and validated in planktonic consortia, were not always in agreement when applied in multispecies biofilms. Discrepancies in culture and molecular outcomes were observed, particularly for triple-species consortia and antibiotic-stressed biofilms. Some differences were observed, such as the higher bacterial counts obtained by q-PCR and/or PNA-FISH (≤4 log10 cells/cm2) compared to culture. But the discrepancies between PNA-FISH and q-PCR data (eg D. pigrum limited assessment by q-PCR) demonstrate the effect of biofilm heterogeneity in method's reliability. As the heterogeneity in biofilms is a reflection of a myriad of variables, tailoring an accurate picture of communities´ changes is crucial. This work demonstrates that at least two, but preferentially three, quantification techniques are required to obtain reliable measures and take comprehensive analysis of polymicrobial biofilm-associated infections.

Localized iron accumulation precedes nucleation and growth of magnetite crystals in magnetotactic bacteria.

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles that originate from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here we address the question: can iron transported inside MTB for the production of magnetite crystals be spatially mapped using electron microscopy? Cultured and uncultured MTB from brackish and freshwater lagoons were studied using analytical transmission electron microscopy in an attempt to answer this question. Scanning transmission electron microscopy was used at sub-nanometric resolution to determine the distribution of elements by implementing high sensitivity energy dispersive X-ray (EDS) mapping and electron energy loss spectroscopy (EELS). EDS mapping showed that magnetosomes are enmeshed in a magnetosomal matrix in which iron accumulates close to the magnetosome forming a continuous layer visually appearing as a corona. EELS, obtained at high spatial resolution, confirmed that iron was present close to and inside the lipid bilayer magnetosome membrane. This study provides important clues to magnetite formation in MTB through the discovery of a mechanism where iron ions accumulate prior to magnetite biomineralization.

Development and nitrate reductase activity of sugarcane inoculated with five diazotrophic strains.

Diazotrophs are able to stimulate plant growth. This study aimed at evaluating the effect of inoculation of five diazotrophic strains on growth promotion and nitrate reductase (NR, EC 1.7.1.1) activity in sugarcane. An experiment was carried out from three stages of cultivation: sprouting, tubes, and in hydroponics. On the first two stages, seven treatments were adopted: uninoculated control; mixed inoculation with five strains; and individual inoculation with Gluconacetobacter diazotrophicus (Gd), Herbaspirillum rubrisubalbicans (Hr), Herbaspirillum seropedicae (Hs), Nitrospirillum amazonense (Na), and Paraburkholderia tropica (Pt). The four treatments showing the best performance were transferred to the hydroponic system for analysis of NR activity. Hs, Pt, and the mixture of all strains led to the highest seedling biomass in tubes, followed by Hr. In hydroponics, the mixture and the strain Hr had the highest growth-promoting effect. NR activity was influenced by inoculation only under low N supply conditions, with positive effect of Hr, Pt, and the mixture.

A marine algicidal Thalassospira and its active substance against the harmful algal bloom species Karenia mikimotoi.

The aim of the present study was to obtain a marine bacterium active against Karenia mikimotoi from the East China Sea and to characterize its extracellular algicidal substances. Using preparative high-performance liquid chromatography (prep-HPLC) and electrospray ionization/quadrupole-time of flight mass spectrometer coupled with a high-performance liquid chromatography (LC/MS-Q-TOF) system, we purified the alga-lysing substance produced by strain ZR-2 and determined its molecular structure. Based on morphology and l6S ribosomal DNA (rDNA) sequence analysis, the ZR-2 strain was highly homologous to Thalassospira species. Algicidal activity against K. mikimotoi was detected in the cell-free filtrate but not in bacterial cells. The alga-lysing substance produced by ZR-2 was ethanol-soluble and thermostable, with a retention time of 6.3 min and a measured elemental composition of C7H5O2 ([M-H](-) ion at m/z 121.0295). The alga-lysing substance produced by ZR-2 was determined to be benzoic acid. Compared with the negative control, both purified ZR-2 bacteria-free filtrate and standard benzoic acid promoted K. mikimotoi cell disruption and induced K. mikimotoi cell content leakage. Our study is the first to report benzoic acid activity against K. mikimotoi as well as production of benzoic acid by a Thalassospira species.

Salt Stress Induced Changes in the Exoproteome of the Halotolerant Bacterium Tistlia consotensis Deciphered by Proteogenomics.

The ability of bacteria to adapt to external osmotic changes is fundamental for their survival. Halotolerant microorganisms, such as Tistlia consotensis, have to cope with continuous fluctuations in the salinity of their natural environments which require effective adaptation strategies against salt stress. Changes of extracellular protein profiles from Tistlia consotensis in conditions of low and high salinities were monitored by proteogenomics using a bacterial draft genome. At low salinity, we detected greater amounts of the HpnM protein which is involved in the biosynthesis of hopanoids. This may represent a novel, and previously unreported, strategy by halotolerant microorganisms to prevent the entry of water into the cell under conditions of low salinity. At high salinity, proteins associated with osmosensing, exclusion of Na+ and transport of compatible solutes, such as glycine betaine or proline are abundant. We also found that, probably in response to the high salt concentration, T. consotensis activated the synthesis of flagella and triggered a chemotactic response neither of which were observed at the salt concentration which is optimal for growth. Our study demonstrates that the exoproteome is an appropriate indicator of adaptive response of T. consotensis to changes in salinity because it allowed the identification of key proteins within its osmoadaptive mechanism that had not previously been detected in its cell proteome.

Skermanella rubra sp. nov., a bacterium isolated from the desert of Xinjiang, China.

A Gram-negative, pink-coloured, rod-shaped, motile bacterium, designated YIM 93097(T), was isolated from the desert soil collected from Xinjiang province of China. Strain YIM 93097(T) was found to grow at 20-45 °C (optimum 28-37 °C), pH 5.0-7.0 (optimum pH 7.0) and 0-8 % (w/v) NaCl (optimum 1 %, w/v). Based on 16S rRNA gene sequence similarity studies, it belongs to the genus Skermanella. The 16S rRNA gene sequence similarity was identified to be 98.7 % to Skermanella xinjiangensis CCTCC AB 207153(T) while the DNA-DNA hybridization value was found to be only 48.1 %. The predominant isoprenoid quinone was determined to be Q-10. The major fatty acids were identified to be C16:0, C18:1 ω7c and summed feature 4 (consisting of C17:1 anteiso B/iso I). The major polar lipids were identified as phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, diphosphatidylglycerol, two unidentified phospholipids and one unidentified aminolipid. The DNA G+C content was found to be 67.2 mol %. The analysis of the genotypic and phenotypic data indicated that strain YIM 93097(T) belongs to a novel species of the genus Skermanella, for which the name Skermanella rubra sp. nov. is proposed. The type strain is YIM 93097(T) (=DSM 21389(T)=CCTCC AB 2015161(T)).

Nitrospirillum irinus sp. nov., a diazotrophic bacterium isolated from the rhizosphere soil of Iris and emended description of the genus Nitrospirillum.

A polyphasic approach was used to characterize a novel nitrogen-fixing bacterial strain, designated YC6995(T), isolated from the rhizosphere soil of Iris ensata var. spontanea (Makino) Nakai inhabiting a wetland located at an altitude of 960 m on Jiri Mountain, Korea. Strain YC6995(T) cells were Gram-negative, and rod-shaped, with motility provided by a single polar flagellum. Optimal growth conditions were 30 °C and pH 7.0. The major fatty acids of strain YC6995(T) were C18:1 ω7c, C18:1 2-OH and C16:0 3-OH. The major respiratory quinone was ubiquinone-10 (Q-10). The polar lipids were phosphatidylethanolamine, phosphatidyldimethylethanolamine, phosphatidylcholine, phosphatidylglycerol and unidentified glycolipids. The genomic DNA G+C content was 64.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed strain YC6995(T) to form a phyletic lineage with Nitrospirillum amazonense DSM 2787(T) with a high sequence similarity (97.2 %), but it displayed low sequence similarity with other remotely related genera, including Azospirillum (<93 %), Rhodocista (93.1-93.4 %), and Skermanella (91.2-93.3 %) in the family Alphaproteobacteria. Based on the phenotypic, chemotaxonomic, and phylogenetic evidences, strain YC6995(T) represents a novel species within the genus Nitrospirillum, for which the name Nitrospirillum irinus sp. nov. is proposed. The type strain is YC6995(T) (= KACC 13777(T) = DSM 22198(T)). An emended description of the genus Nitrospirillum is also proposed.

The influence of protozoa with a filtered and non-filtered seawater culture of Tetraselmis sp., and effects to the bacterial and algal communities over 10 days.

In this study a filter was used to remove protozoa and its effects on a Tetraselmis sp. culture were evaluated in terms of final total lipid, final total dry weight, cell counts, and both the bacterial and algal communities. The protozoa species observed within this study was identified as Cohnilembus reniformis. It was observed that on the final day no C. reniformis were present in filtered cultures compared to the non-filtered culture which contained 40±3 C. reniformis/mL. The presence of C. reniformis within the culture did not affect the total lipid or the total dry weight recovered, suggesting that Tetraselmis sp. was capable of surviving and growing in the presence of C. reniformis. Overall it is suggested that an 11 µm filter was effective at removing protozoa, though growing a microalgae culture without filtration did not show any significant effect.

Description of Niveispirillum fermenti gen. nov., sp. nov., isolated from a fermentor in Taiwan, transfer of Azospirillum irakense (1989) as Niveispirillum irakense comb. nov., and reclassification of Azospirillum amazonense (1983) as Nitrospirillum amazonense gen. nov.

A taxonomic study was carried out on a novel aerobic bacterial strain (designated CC-LY736(T)) isolated from a fermentor in Taiwan. Cells of strain CC-LY736(T) were Gram-stain negative, spiral-shaped and motile by means of a monopolar flagellum. Strain CC-LY736(T) shared the greatest degree of 16S rRNA gene sequence similarity to Azospirillum irakense DSM 11586(T) (97.2 %), Rhodocista centenaria JCM 21060(T) (96.3 %) and Rhodocista pekingensis JCM 11669(T) (96.1 %). The major fatty acids were C16:0, C16:1 ω5c, C19:0 cyclo ω8c, C18:1 ω7c/C18:1 ω6c, C16:0 3-OH and C18:1 2-OH. The predominant polar lipids included phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidyldimethylethanolamine and two unidentified glycolipids. The common major respiratory quinone was ubiquinone Q-10 and predominant polyamines were sym-homospermidine and putrescine. The DNA G+C content of strain CC-LY736(T) was 67.6 ± 0.1 mol %. During phylogenetic analysis, strain CC-LY736(T) formed a unique phyletic lineage associated with Rhodocista species. However, the combination of genetic, chemotaxonomic and physiological data clearly indicated that strain CC-LY736(T) was a novel representative of the family Rhodospirillaceae. Based on the polyphasic comparison, the name Niveispirillum fermenti gen. nov., sp. nov. is proposed; the type strain of the type species is CC-LY736(T) (= BCRC 80504(T) = LMG 27263(T)). In addition, the reclassifications of Azospirillum irakense as Niveispirillum irakense comb. nov. (type strain KBC1(T) = ATCC 51182(T) = BCRC 15764(T) = CIP 103311(T)), and Azospirillum amazonense as Nitrospirillum amazonense gen. nov., sp. nov. (type strain Am14(T) = ATCC 35119(T) = BCRC 14279(T) = DSM 3787(T)) are proposed based on the polyphasic taxonomic data obtained in this study.

Dongia rigui sp. nov., isolated from freshwater of a large wetland in Korea.

A motile, curved to twisted rod-shaped aerobic bacterium, designated strain 04SU4-P(T), was isolated from freshwater collected from the Woopo wetland (Republic of Korea). Cells were observed to be Gram-stain negative, catalase negative and oxidase positive. The major fatty acids (>10 % of the total) were identified as C19:0 ω8c cyclo (24.6 %), C16:0 (24.3 %) and C18:1 ω7c (13.1 %). The DNA G+C content was determined to be 71.5 mol%. The major polar lipids were identified as phosphatidylglycerol, phosphatidylethanolamine, one unknown phospholipid and one unknown aminolipid. The major ubiquinone was determined to be Q-10. A phylogenetic tree based on 16S rRNA gene sequences showed that strain 04SU4-P(T) forms an evolutionary lineage within the genus Dongia and its nearest neighbour is Dongia mobilis LM22(T) (98.0 % sequence similarity). Genomic DNA-DNA hybridization of stain 04SU4-P(T) with D. mobilis LM22(T) showed relatedness of only 34.2 %. The phenotypic characteristics indicate the strain 04SU4-P(T) can be distinguished from the sole member of the genus Dongia. On the basis of the data presented in this study, strain 04SU4-P(T) represents a novel species, for which the name Dongia rigui is proposed. The type strain is 04SU4-P(T) (KCTC 23341(T) = JCM 17521(T)).

Organic carbon recovery and photosynthetic bacteria population in an anaerobic membrane photo-bioreactor treating food processing wastewater.

Purple non-sulfur bacteria (PNSB) were cultivated by food industry wastewater in the anaerobic membrane photo-bioreactor. Organic removal and biomass production and characteristics were accomplished via an explicit examination of the long term performance of the photo-bioreactor fed with real wastewater. With the support of infra-red light transmitting filter, PNSB could survive and maintain in the system even under the continual fluctuations of influent wastewater characteristics. The average BOD and COD removal efficiencies were found at the moderate range of 51% and 58%, respectively. Observed photosynthetic biomass yield was 0.6g dried solid/g BOD with crude protein content of 0.41 g/g dried solid. Denaturing gradient gel electrophoretic analysis (DGGE) and 16S rDNA sequencing revealed the presence of Rhodopseudomonas palustris and significant changes in the photosynthetic bacterial community within the system.

Genome streamlining and chemical defense in a coral reef symbiosis.

Secondary metabolites are ubiquitous in bacteria, but by definition, they are thought to be nonessential. Highly toxic secondary metabolites such as patellazoles have been isolated from marine tunicates, where their exceptional potency and abundance implies a role in chemical defense, but their biological source is unknown. Here, we describe the association of the tunicate Lissoclinum patella with a symbiotic α-proteobacterium, Candidatus Endolissoclinum faulkneri, and present chemical and biological evidence that the bacterium synthesizes patellazoles. We sequenced and assembled the complete Ca. E. faulkneri genome, directly from metagenomic DNA obtained from the tunicate, where it accounted for 0.6% of sequence data. We show that the large patellazoles biosynthetic pathway is maintained, whereas the remainder of the genome is undergoing extensive streamlining to eliminate unneeded genes. The preservation of this pathway in streamlined bacteria demonstrates that secondary metabolism is an essential component of the symbiotic interaction.

Antibiotic resistance of mixed biofilms in cystic fibrosis: impact of emerging microorganisms on treatment of infection.

Cystic fibrosis (CF) is a genetic disorder associated with multispecies infections where interactions between classical and newly identified bacteria might be crucial to understanding the persistent colonisation in CF lungs. This study investigated the interactions between two emerging species, Inquilinus limosus and Dolosigranulum pigrum, and the conventional CF pathogen Pseudomonas aeruginosa by evaluating the ability to develop biofilms of mixed populations and then studying their susceptibility patterns to eight different antimicrobials. Monospecies biofilms formed by I. limosus and D. pigrum produced significantly less biomass than P. aeruginosa and displayed greater sensitivity to antimicrobials. However, when in dual-species biofilms with P. aeruginosa, the emerging species I. limosus and D. pigrum were crucial in increasing tolerance of the overall consortia to most antibiotics, even without a change in the number of biofilm-encased cells. These results may suggest that revising these and other species interactions in CF might enable the development of more suitable and effective therapies in the future.

Draft genome sequence of the purple photosynthetic bacterium Phaeospirillum molischianum DSM120, a particularly versatile bacterium.

Here we present the draft genome sequence of the versatile and adaptable purple photosynthetic bacterium Phaeospirillum molischianum DSM120. This study advances the understanding of the adaptability of this bacterium, as well as the differences between the Phaeospirillum and Rhodospirillum genera.

Caenispirillum salinarum sp. nov., a member of the family Rhodospirillaceae isolated from a solar saltern.

A novel Gram-negative, vibrio-shaped, motile bacterium, designated strain AK4(T), was isolated from a sediment sample collected from a solar saltern at Kakinada, Andhra Pradesh, India. Strain AK4(T) was positive for oxidase, urease and DNase activities but negative for gelatinase, catalase, ornithine decarboxylase, lysine decarboxylase, nitrate reduction, aesculin, indole and lipase activities. The fatty acids were dominated by unsaturated components, with a high abundance of summed feature 8 (C(18:1)ω7c and/or C(18:1)ω6c) and C(17:1)ω6c. Strain AK4(T) contained Q-10 as the major respiratory quinone and phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine as major polar lipids. The DNA G+C content of strain AK4(T) was 71.0 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain AK4(T) was most closely related to the type strain of Caenispirillum bisanense of the family Rhodospirillaceae (phylum 'Proteobacteria') (96.6% sequence similarity). It shared <93.2% 16S rRNA gene sequence similarity with other members of the family. Based on phenotypic characteristics and phylogenetic inference, strain AK4(T) is considered to represent a novel species of the genus Caenispirillum, for which the name Caenispirillum salinarum sp. nov. is proposed; the type strain is AK4(T) (=MTCC 10963(T)=JCM 17360(T)).

Phaeospirillum tilakii sp. nov., a phototrophic alphaproteobacterium isolated from aquatic sediments.

Two strains (JA492(T) and JA590) of spiral-shaped, anaerobic, Gram-stain-negative, motile, purple non-sulfur bacteria were isolated from aquatic sediments from a bird sanctuary and a stream, respectively, and were characterized by a polyphasic taxonomic approach. Bacteriochlorophyll a and carotenoids (rhodopin, lycopene, hydroxylycopene glucoside and dihydroxylycopene diglucoside) were present as photosynthetic pigments. Intracellular photosynthetic membranes were of the stacked type. The major fatty acids were C(18 : 1)ω7c, C(16 : 0) and summed feature 3 (C(16 : 1)ω6c and/or C(16 : 1)ω7c) in both strains. Ubiquinones and menaquinones were present as major quinone components. The genomic DNA G+C contents of strains JA492(T) and JA590 were 63.8 and 61.5 mol%, respectively. Both strains were closely related (mean DNA-DNA hybridization >70 %). Phylogenetic analysis showed that the strains clustered with species of the genus Phaeospirillum of the family Rhodospirillaceae, class Alphaproteobacteria. Based on 16S rRNA gene sequence analysis, both strains showed highest sequence similarity with Phaeospirillum oryzae JA317(T) (97.2-97.4 %), Phaeospirillum molischianum DSM 120(T) (96.5-96.7 %), Phaeospirillum fulvum DSM 113(T) (96.7-96.9 %) and Phaeospirillum chandramohanii JA145(T) (96.5-96.7 %). DNA-DNA relatedness between strain JA492(T) and its closest relative in the genus Phaeospirillum was less than 42 %. It is evident from phenotypic, chemotaxonomic and molecular genetic data that strain JA492(T) represents a novel species of the genus Phaeospirillum, for which the name Phaeospirillum tilakii sp. nov. is proposed; the type strain is JA492(T) ( = NBRC 107650(T) = KCTC 15012(T)).

Thalassospira sp. isolated from the oligotrophic eastern Mediterranean Sea exhibits chemotaxis toward inorganic phosphate during starvation.

The eastern Mediterranean Sea represents an ultraoligotrophic environment where soluble phosphate limits the growth of bacterioplankton. Correspondingly, genes coding for high-affinity phosphate uptake systems and for organophosphonate utilization are highly prevalent in the plankton metagenome. Chemotaxis toward inorganic phosphate constitutes an alternative strategy to cope with phosphate limitation, but so far has only been demonstrated for two bacterial pathogens and an archaeon, and not in any free-living planktonic bacterium. In the present study, bacteria affiliated with the genus Thalassospira were found to constitute a regular, low-abundance member of the bacterioplankton that can be detected throughout the water column of the eastern Mediterranean Sea. A representative (strain EM) was isolated in pure culture and exhibited a strong positive chemotaxis toward inorganic phosphate that was induced exclusively in phosphate-starved cultures. Phosphate-depleted cells were 2-fold larger than in exponentially growing cultures, and 43% of the cells retained their motility even during prolonged starvation over 10 days. In addition, Thalassospira sp. strain EM was chemotactically attracted by complex substrates (yeast extract and peptone), amino acids, and 2-aminoethylphosphonate but not by sugar monomers. Similarly to the isolate from the eastern Mediterranean, chemotaxis toward phosphate was observed in starved cultures of the other two available isolates of the genus, T. lucentensis DSM 14000T and T. profundimaris WP0211T. Although Thalassospira sp. represents only up to 1.2% of the total bacterioplankton community in the water column of the eastern Mediterranean Sea, its chemotactic behavior potentially leads to an acceleration of nutrient cycling and may also explain the persistence of marine copiotrophs in this extremely nutrient-limited environment.