Strain N1 Research Articles

Effects of cacao swollen shoot virus mild strains N1 and SS365B on growth and yield of cacao - a follow-up report

The cumulative effects of cacao swollen shoot virus (CSSV) mild strains N1 and SS365B on growth and yield of cacao (Theobroma cacao L.) were evaluated in a 12-year field trial at the Cocoa Research Institute of Ghana (CRIG). The treatments consisted of mixed hybrid cacao plants inoculated with N1 or SS365B prior to sowing and a non-inoculated control. Growth of mild strain-inoculated cacao plants did not differ significantly from that of non-inoculated plants. However, growth of N1-inoculated cacao plants was significantly higher than that of SS365B-inoculated ones. The yield of N1-inoculated cacao plants did not differ significantly from that of the non-inoculated plants. However, yield of SS365B-inoculated plants was significantly lower compared to N1-inoculated and the non-inoculated plants. In comparison with the non-inoculated control, yield was 77% and 20% lower in SS365B- and N1-inoculated cacao plants, respectively. Virus indexing conducted over a period of six months on randomly collected budwood from the field revealed the presence of mixed infection of CSSV strains in the field. Cacao tree mortality did not differ among the treatments. These results provide further evidence that the CSSV mild strain N1 is milder in its effect on cacao growth and yield than SS365B and suggest that the former would be a more suitable candidate for cross protection in cacao.

Absence of the nahG-like gene caused the syntrophic interaction between Marinobacter and other microbes in PAH-degrading process

In this study, Marinobacter sp. N4 isolated from the halophilic consortium CY-1 was found to degrade phenanthrene as a sole carbon source with the accumulation of 1-Hydroxy-2-naphthoic acid (1H2N). With the assistance of Halomonas sp. G29, phenanthrene could be completely mineralized. The hpah1 and hpah2 gene cluster was amplified from the genome of strain N4, that were responsible for upstream and downstream of PAH degradation. Strain N4 was predicted for the transformation from phenanthrene to 1H2N, and strain G29 could transform the produced 1H2N into 1,2-dihydroxynaphthalene (1,2-DHN). The produced 1,2-DHN could be further transformed into salicylic acid (SALA) by strain N4. SALA could be catalyzed into catechol by strain G29 and further utilized by strains N4 and G29 via the catechol 2,3-dioxygenase pathway and catechol 1,2-dioxygenase pathway, respectively. NahG, encoding salicylate hydroxylase, was absent from the hpah2 gene cluster and predicted to be the reason for 1H2N accumulation in the PAH-degrading process by pure culture of strain N4. The syntrophic interaction mode among Marinobacter and other microbes was also predicted. According to our knowledge, this is the first report of the PAH-degrading gene cluster in Marinobacter and the syntrophic interaction between Marinobacter and other microbes in the PAH-degrading process.

Spatiotemporal Spread of Cacao Swollen Shoot Virus Severe Strain 1A in Mixed Hybrid Cacao Pre-inoculated With Mild Strain N1.

The spatiotemporal spread of cocoa swollen shoot virus disease (CSSVD), which is caused by cacao swollen shoot virus (CSSV) severe strain 1A in mixed hybrid cacao pre-inoculated with CSSV mild strain N1 (CSSV-N1), was investigated during a field experiment from 2006 to 2017, at the Cocoa Research Institute of Ghana. The development of disease epidemics has been described by the use of statistical modeling. Protecting all cacao plants with CSSV-N1 reduced the rate of CSSV-1A symptom appearance by 43% (P = 0.05) compared with the nonprotected control and by 33% compared with plots where cacao plants in the outer three or five rows were protected with CSSV-N1. Similarly, creating the protective outer rings three or five rows deep reduced the rate of CSSV-1A symptoms by 14% (P = 0.05) compared with the nonprotected control. CSSV-1A epidemics increased approximately 18% faster (P = 0.05) in transects oriented from the north and east compared with those oriented from the south and west. During the last 2 years of the study, CSSVD spread decreased significantly (P = 0.05) faster in plots where all test cacao plants were inoculated with CSSV-N1 compared with other treatments. The growth of cacao did not differ significantly among the treatments over the 9-year assessment period. Similarly, differences in the cumulative yield among the treatments over the 8-year assessment period were not significant.

Identification of Key Residues Required for RNA Silencing Suppressor Activity of p23 Protein from a Mild Strain of Citrus Tristeza Virus.

The severe strain of citrus tristeza virus (CTV) causes quick decline of citrus trees. However, the CTV mild strain causes no symptoms and commonly presents in citrus trees. Viral suppressor of RNA silencing (VSR) plays an important role in the successful invasion of viruses into plants. For CTV, VSR has mostly been studied in severe strains. In this study, the N4 mild strain in China was sequenced and found to have high sequence identity with the T30 strain. Furthermore, we verified the functions of three VSRs in the N4 strain, and p23 was found to be the most effective in terms of local silencing suppressor activity among the three CTV VSRs and localized to both nucleus and plasmodesmata, which is similar to CTV T36 strain. Several conserved amino acids were identified in p23. Mutation of E95A/V96A and M99A/L100AA impaired p23 protein stability. Consequently, these two mutants lost most of its suppressor activity and their protein levels could not be rescued by co-expressing p19. Q93A and R143A/E144A abolished p23 suppressor activity only and their protein levels increased to wild type level when co-expressed with p19. This work may facilitate a better understanding of the pathogenic mechanism of CTV mild strains.

Production of Anserine-Rich Fish Sauce from Giant Masu Salmon, Oncorhynchus masou masou and γ-Aminobutyric Acid (GABA)-Enrichment by Lactobacillus plantarum Strain N10

Previously, we developed a novel production technique for giant masu salmon (GMS). This study aimed to develop a fish sauce from GMS to explore ways to efficiently utilize the salmon and to enrich the fish sauce with γ-aminobutyric acid (GABA) by microbial fermentation. The minced bodies of GMS were autolyzed by endogenous protease at 55 °C and 60 °C. During autolysis, the changes in total free amino acids and protein size was monitored by LC-MS and SDS-PAGE analysis, respectively. After 96 h, fish sauce was prepared by heating, and the amino acid composition was analyzed by LC-MS. To enrich the fish sauce with GABA, Lactobacillus plantarum strain N10 was added and incubated at 28 °C for 48 h. The total free amino acids content significantly increased for 96 h. SDS-PAGE analysis showed that major bands at 200 kDa and 48 kDa detected at 0 h gradually disappeared over time. The ratio of anserine to total amino acids in the fish sauce was approximately 36%. The concentration of GABA in the fish sauce significantly increased through the addition of strain N10. Thus, anserine-rich fish sauce could be quickly produced from GMS, and the fish sauce was enriched with GABA by microbial fermentation.

GENETIC DIVERSITY OF ECHINOCOCCUS MULTILOCULARIS CESTODES IN EUROPE AS DETERMINED BY MITOCHONDRIAL AND NUCLEAR SEQUENCES

Alveolar echinococcosis caused by metacestode stage of the tapeworm Echinococcus multilocularis is considered as one of the most pathogenic zoonoses in temperate and arctic regions. To more thoroughly ascertain genetic diversity in E. multilocularis tapeworms from Europe and to indicate transmission patterns of parasite, 25 isolates from a contiguous territory of eight European countries were subjected to sequencing of mitochondrial and nuclear DNA. A total of 2 715 nucleotide sequences in nad1, cox1, rrnS, atp6 and actII genes were screened in the current study. Whereas in 24 isolates profiles belonging to a previously described European clade were identified, the interesting feature was related to the detection of the form being close to North American strain N1 (that appeared to have lower zoonotic potential) in Austrian patient. The known occurrence of this variant has thus extended from the St. Lawrence Island in the Bering Sea and Russian isolates in Yakutia to central Europe. The finding indicates that N1 genotype has not only circumpolar trans-Beringian distribution, but during glacial events in Pleistocene a more southerly fox dispersal has likely transmitted N1 into central Europe. Further distinguished genotype was confined to four isolates from southern Germany (mountain range of Swabian Jura) and had five substitutions compared to the main European form. One Latvian isolate had two mutations in cox1, one of which was identical to German isolates from Feldstetten. Single nucleotide polymorphisms were detected in single isolates from Slovakia, Hungary and France in cox1 and actIIgenes. Lower genetic diversity detected in the examined isolates in more peripheral zones of its European distribution has supported Knapp ́s model (2009) suggesting that parasite focus in Europe is governed by “mainland-island” transmission where ancestral foci supply hitherto non-endemic areas by dispersal generated by fox mobility and migration.

Draft Genome Sequence of Chlorobium sp. Strain N1, a Marine Fe(II)-Oxidizing Green Sulfur Bacterium.

Here, we present the draft genome sequence of the halotolerant photoferrotroph Chlorobium sp. strain N1. This draft genome provides insights into the genomic potential of the only marine Fe(II)-oxidizing green sulfur bacterium (GSB) available in culture and expands our views on the metabolic capabilities of Fe(II)-oxidizing GSB more generally.

Molecular Phylogeny and Phenotypic Characterization of Yeasts with a Broad Range of pH Tolerance Isolated from Natural Aquatic Environments

In this study, yeasts with broad range of pH tolerance were isolated and characterized from natural aquatic environments in Japan. Only a few basic and application studies of alkali-tolerant yeasts have been reported, despite the unmet industrial needs. First, we surveyed alkali-tolerant yeasts from natural aquatic environments at pH 7.6 - 9.4. We isolated 35 yeast strains that grew in pH 9.0 medium, from seven genera and nine species: 25 strains (N1, N2, through N6, N9, K1, K3 through K19) were Rhodotorula mucilaginosa; one (N7) was Rhodosporidium fluvial; one (N8) was Scheffersomyces spartinae; two (N10 and N13) were Wicherhamonyces anomalus; one (N11) was Cyberlindnera saturnus; one (S1) was Candida sp.; two (S2 and S4) were Candida intermedia; one (S3) was Candida quercuum; and one (K2) was Cryptococcus liquefacience. We examined the effects of pH on the growth of representative yeast strains. Strains K12 and S4 showed high growth at pH 3 - 10. Strains N7, N8, N10, N11, and S3 showed high growth at pH 3 - 9. Strains K2 and S1 showed high growth at pH 4 - 8. All nine of these strains had neutralizing activities from acidic media at pH 3 - 5 to pH 6 - 8. We previously isolated acid-tolerant yeasts (Cryptococcus sp. T1 [1] and Candida intermedia CeA16 [2]) from extremely acidified environments; they showed high growth at pH 3 - 9 and neutralizing activities of acidic media by releasing ammonium ions. Thus, alkali-tolerant yeasts and acid-tolerant yeasts were found to be similar species and have both high growth at a broad range of pH and neutralizing activities of acid media. Previously, we also isolated acid-tolerant, acid-neutralizing yeasts from neutral natural environments (26 strains, 12 species) [3]. Next, we constructed the phylogenetic trees of both acid-tolerant yeasts and alkali-tolerant yeasts. All were situated in the same classification position. Similar yeast species with a broad range of pH tolerance were living in natural aquatic environments at pH values from alkali to acid.

Characterization of a Newly Isolated Strain Pseudomonas sp. N3 for Denitrification at Low Temperature

Based on traditional microbiological methods, a novel denitrifier Pseudomonas sp. N3 with excellent denitrification capacity at low temperature was isolated and identified using phenotypic and phylogenetic analysis. Complete nitrate removal was achieved at C/N=8, that is, 70 mg·L-1 nitrate. In addition, the isolate exhibited a great adaptability for low temperature and can reach 100% removal of 15 mg·L-1 nitrate at a temperature as low as 4℃ within 36 h. The denitrification genes of narG and nirS were highly expressed; they were at the same order of magnitude as those at 30℃. Semicontinuous experiments were conducted to test the stability of N3 immobilized with polyvinyl alcohol and sodium alginate at 10℃. The results show that immobilized N3 can remove 15 mg·L-1 nitrate completely within three days and maintains a strong mechanical performance and stability during the whole 54 days. The cold resistance and high denitrification ability of the strain N3 make it applicable to nitrogen wastewater treatment in winter.

Isolation and characterization of a marine testosterone-degrading bacterium: Vibrio sp. N3

Steroids, including testosterone, estrone, 17β-estradiol, estriol and 17β-ethinyl estradiol, are harmful not only to the population dynamics of aquatic life forms but also to public health. In this study, a marine testosterone-degrading bacterium (strain N3) was isolated from Nanao Island in the South China Sea. In addition, the strain could also use 17β-estradiol (E2), 17β-ethinyl estradiol (EE2), estriol (E3) or cholesterol as a sole carbon source. According to the 16S rRNA gene sequence analysis, strain N3 was identified as Vibrio sp. Further characterization showed that the strain is aerobic, gram-negative, and mobile and exhibits resistance to ampicillin, carbenicillin, penicillin and spectinomycin. For enhancing its capacity of testosterone degradation, the Plackett–Burman factorial design and the central composite design were used to optimize the culture condition. Under optimal conditions, 92% of testosterone was degraded by Vibrio sp. N3 in 48h.

Expression of normal stress difference and relaxation modulus for ternary nanocomposites containing biodegradable polymers and carbon nanotubes by storage and loss modulus data

In this paper, the first normal stress differences (N1) and the relaxation modulus (G (t)) are predicted for prepared poly (lactic acid) (PLA)/poly (ethylene oxide) (PEO)/carbon nanotubes (CNT) nanocomposites using the experimental results of storage and loss moduli. N1 and G (t) are calculated for these samples as a function of shear rate. Moreover, the effects of various parameters on N1 and G (t) are revealed to validate the equations. N1 increases by shear rate, but it shows a plateau at low shear rates. The addition of nanoparticles to the blends increases N1 demonstrating that the nanoparticles enhance the elasticity. G (t) decreases upon increasing in the shear rate in all samples and the addition of CNT to polymer blends causes a high G (t). A high storage modulus and small loss modulus enhance N1 and G (t), whereas poor storage modulus lowers N1 and G (t). Additionally, G (t) improves significantly at small strain and high N1. This work presents useful guidelines for calculation of N1 and G (t) and understanding the origin of these terms in polymer systems.

Calcium carbonate precipitation induced by calcifying bacteria in culture experiments: Influence of the medium on morphology and mineralogy

Bacterially induced calcium carbonate precipitation, recognized as a common phenomenon in nature, has been extensively investigated owing to its beneficial and harmful effects on calcareous stones, namely environmental friendly and potential approach for consolidation deteriorated artworks and aesthetic and physicochemical damage to intact stones. Here four bacterial strains, identified as Pseudomonas sp. (N9), Bacillus cereus (T6), Lysinibacillus sphaericus (T5) and Bacillus sp. (T4), were isolated from white plaques covering historical white marble and proven to have the ability to induce precipitations of calcium carbonate. However, the size and morphology of crystals exhibit a distinct difference after inoculation of specific strain, even in the presence of same medium the crystals tend to vary with different isolates. XRD analysis shows that both calcite and vaterite were simultaneously present in strains N9- and T6-inoculated M-3P medium, while only calcite was detected in M-3P medium after inoculation with strains T5 and T4. Interestingly, in strains T6-and T5-inoculated B-4 culture medium, the precipitations were mainly composed of calcite and vaterite, with a small amount of weddellite only obtained from the former, while calcium-containing crystals were also absent from strains N9- and T4-inoculated medium. Moreover, all of the precipitated crystals present in both culture medium correspond to pH analyses.

Cloning, expression and characterization of cold active esterase (EstN7) from Bacillus cohnii strain N1: A novel member of family IV

Esterases and lipases from extremophiles have attracted great attention due to their unique characteristics and wide applications. In the present study, an open reading frame (ORF) encoding a novel cold active esterase (EstN7) from Bacillus cohnii strain N1 was cloned and expressed in Escherichia coli. The full-length esterase gene encoding a protein of 320 amino acids with estimated molecular weight of 37.0 kDa. Amino acid sequence analysis revealed that the EstN7 belongs to family IV lipases with a characteristic penta-peptide motif (GXSXG), the catalytic triad Ser, Asp, His and the conserved HGGG motif of the family IV. The recombinant enzyme was purified to apparent homogeneity using nickel-affinity chromatography with a purification fold of 5 and recovery 94.5%. The specific activity of the purified enzyme was 336.89 U/mg. The recombinant EstN7 showed optimal activity at 5 °C moreover, EstN7 displayed full robust stability in the presence of wide range of organic solvents. The purified enzyme had Km and Vmax of 45 ± 0.019 μM and 1113 μmol min−1 mg−1, respectively on p-NP-acetate. These promising characteristics of the recombinant EstN7 would underpin its possible usage with high potential in the synthesis of fragile compounds in pharmaceutical industries.

The effects of mild cacao swollen shoot virus strains N1 and SS365B on growth and yield of cacao

A field experiment started at the Cocoa Research Institute of Ghana in 2007 to investigate the effects of the cacao swollen shoot virus (CSSV) mild stains N1 and SS365B on growth and yield of mixed hybrid cacao (Theobroma cacao L.). Growth was significantly influenced by the duration of infection with the two CSSV mild strains. Slicing analyses showed no significant differences in stem circumference among treatments up to the third year of field data collection. However, from the fourth to the seventh year, growth of N1-inoculated cacao plants was significantly higher than that of SS365B-inoculated plants. Overall, growth did not differ significantly between cacao plants inoculated with mild strain and the non-inoculated plants. Contrary to some previous reports, yield of mild strain-inoculated cacao plants was significantly lower than that of the non-inoculated plants. Polymerase chain reaction was used to detect the presence of CSSV in randomly selected field samples. The implications of these results (based on field data collected from 2008 to 2014) in the management of cocoa swollen shoot virus disease in Ghana are discussed.

Morphological and electrophysiological differences in tarsal chemosensilla between the wild silkmoth Bombyx mandarina and the domesticated species Bombyx mori

Gustatory and olfactory senses of phytophagous insects play important roles in the recognition of host plants. In the domestic silkmoth Bombyx mori and its wild species Bombyx mandarina, the morphologies and responses of adult olfactory organs (antennae) have been intensely investigated. However, little is known about these features of adult gustatory organs and the influence of domestication on the gustatory sense. Here we revealed that both species have two types of sensilla (thick [T] and slim [S] types) on the fifth tarsomeres of the adult legs. In both species, females have 3.6–6.9 times more T-sensilla than males. Therefore, T-sensilla seem to play more important roles in females than in males. Moreover, gustatory cells of T-sensilla of B. mandarina females responded intensely to mulberry leaf extract in electrophysiological experiments, while T-sensilla of B. mori females (N4 strain) hardly responded to mulberry leaf extract. These results suggest that T-sensilla of B. mandarina females are involved in the recognition of oviposition sites. We also observed that, in three B. mori strains (N4, p50T, and Kinshu × Showa), the densities of sensilla on the fifth tarsomeres were much lower than in B. mandarina. These results indicate that domestication has influenced the tarsal gustatory system of B. mori.

Probiotic effect ofStreptomycesspp. on shrimp (Litopenaeus vannamei) postlarvae challenged withVibrio parahaemolyticus

The effect of Streptomyces strains RL8 and N7 on the growth, survival and histological structure of the hepatopancreas of Litopenaeus vannamei was determined. Shrimp post-larvae of 0.02 ± 0.01 g were fed with diets supplemented with Streptomyces spp. RL8 and N7 at 108 CFU g⁻1 of feed for 30 days, followed by challenge with Vibrio parahaemolyticus. Toxicity was also assessed by recording the mortality associated with the use of 1-100 g/L of cell mass and 108-1010 CFU/g of feed of these strains in Artemia salina and L. vannamei, respectively. The group treated with Streptomyces sp. RL8 had significantly better weight gain (0.62 ± 0.18 g) and survival rates (84.44 ± 5.7%) after challenge, whereas the one fed with Streptomyces sp. N7 showed significantly higher survival rate (57.77 ± 6.8%) than the control group (0.55 ± 0.20 g and 11.11 ± 9.0%, respectively). The hepatopancreas of Streptomyces-fed shrimps showed better histological integrity with significantly lower degree of atrophy and necrotic tubules than their unfed counterpart. No toxicity associated with these strains was found. Consequently, they can be excellent probiotic candidates to improve the physiological status and prevent infectious diseases of cultured L. vannamei.

Isolation of lignocellulose-derived sugars, co-fermentation of lactic acid bacteria strains, and evaluation of L-lactic acid productivity

High-productivity lactic acid bacteria (LAB) strains were screened and their capability to ferment lignocellulose-derived sugars into lactic acid were evaluated. Fifteen LAB strains were successfully isolated from cow dung, haystack, and sheep manure, respectively. Four relatively good strains were selected based on Gram stain, colony morphology, and catalase activity tests. The four strains and commercial inoculants (Lactobacillus pentosus and Enterococcus faecalis) were used to ferment cellobiose/ glucose/xylose to produce high-purity L-lactic acid. One of the strains (N4) presented the highest production of L-lactic acid after fermentation for 12 h and showed a L-lactic acid production of 15.1 g/L, 18.5 g/L, and 2.8 g/L and a productivity of 1.01 g∙L−1∙h−1, 3.68 g∙L−1∙h−1, and 0.47 g∙L−1∙h−1 by metabolizing cellobiose, glucose, and xylose, respectively. Through a phylogenetic tree analysis, strain N4 was identified as Enterococcus faecium and named Enterococcus faecium N4. Enterococcus faecium N4 has a great potential to ferment lignocellulose-derived sugars into L-lactic acid.

Diversity and screening of lactic acid bacteria in la-baicai made by Korean-Chinese in northeastern China

ABSTRACTThis study investigated the lactic acid bacteria (LAB) population in la-baicai (spicy cabbage), a traditional fermented food made by the Korean-Chinese community in northeastern China and screened for functional LAB. LAB diversity was analyzed using denaturing gradient gel electrophoresis (DGGE), and 81 LAB strains were isolated and identified based on 16S rDNA sequencing analysis. Polymerase chain reaction DGGE detected 21 LAB species, belonging to the genera Lactobacillus (Lb.), Leuconostoc (Leu.), Pediococcus and Weissella, in 45 la-baicai samples. Lb. plantarum and Lb. sakei were considered to be dominant in the bacterial community. Among 81 LAB isolated by traditional pure culture methods were Lb. plantarum (25 strains), Lb. brevis (two strains), Lb. casei, (four strains), Lb. pentosus (three strains), Enterococcus faecium (45 strains), and E. durans (two strains). The tolerances of these LAB were investigated. Six LAB with high salt (NaCl)-tolerance were screened from the isolates, and 16% (w/v) was the highest salt-tolerance reached. Among the isolates, strain N1, identified as Lb. pentosus, survived well in a simulated digestive environment. Traditional fermented la-baicai from northeastern China is a rich LAB resource. Further study is needed and would be worthwhile to advance the benefits of these LAB.

Physiological characterization of a halotolerant anoxygenic phototrophic Fe(II)-oxidizing green-sulfur bacterium isolated from a marine sediment.

Anoxygenic photoautotrophic bacteria which use light energy and electrons from Fe(II) for growth, so-called photoferrotrophs, are suggested to have been amongst the first phototrophic microorganisms on Earth and to have contributed to the deposition of sedimentary iron mineral deposits, i.e. banded iron formations. To date only two isolates of marine photoferrotrophic bacteria exist, both of which are closely related purple non-sulfur bacteria. Here we present a novel green-sulfur photoautotrophic Fe(II) oxidizer isolated from a marine coastal sediment, Chlorobium sp. strain N1, which is closely related to the freshwater green-sulfur bacterium Chlorobium luteolum DSM273 that is incapable of Fe(II) oxidation. Besides Fe(II), our isolated strain grew phototrophically with other inorganic and organic substrates such as sulfide, hydrogen, lactate or yeast extract. Highest Fe(II) oxidation rates were measured at pH 7.0-7.3, the temperature optimum was 25°C. Mössbauer spectroscopy identified ferrihydrite as the main Fe(III) mineral and fluorescence and helium-ion microscopy revealed cell-mineral aggregates without obvious cell encrustation. In summary, our study showed that the new isolate is physiologically adapted to the conditions of its natural habitat but also to conditions as proposed for early Earth and is thus a suitable model organism for further studies addressing phototrophic Fe(II) oxidation on early Earth.

Streptomyces effect on the bacterial microbiota associated to Crassostrea sikamea oyster.

To determine the composition and diversity of the microbiota associated to Crassostrea sikamea treated during 30days with Streptomyces strains N7 and RL8. DNA was extracted from oysters followed by 16S rRNA gene amplification and pyrosequencing. The highest and lowest species diversity richness was observed in the initial and final control group, whereas Streptomyces-treated oysters exhibited intermediate values. Proteobacteria was the most abundant phylum (81·4-95·1%), followed by Bacteroidetes, Actinobacteria and Firmicutes. The genera Anderseniella, Oceanicola, Roseovarius, Ruegeria, Sulfitobacter, Granulosicoccus and Marinicella encompassed the core microbiota of all experimental groups. The genus Bacteriovorax was detected in all groups except in the final control and the depurated N7, whereas Vibrio remained undetected in all Streptomyces-treated groups. RL8 was the only group that harboured the genus Streptomyces in its microbiota. Principal component analysis showed that Streptomyces strains significantly changed oyster microbiota with respect to the initial and final control. Crassostrea sikamea treated with Streptomyces showed high species diversity and a microbiota composition shift, characterized by keeping the predator genus Bacteriovorax and decreasing the pathogenic Vibrio. This is the first culture-independent study showing the effect of Streptomyces over the oyster microbiota. It also sheds light about the potential use of Streptomyces to improve mollusc health and safety for consumers after the depuration process.