Arthrobacter bergerei sp. nov. and Arthrobacter arilaitensis sp. nov., novel coryneform species isolated from the surfaces of cheeses

The Microbial Diversity on the Surface of Smear-Ripened Cheeses and Its Impact on Cheese Quality and Safety

Smear-ripened cheeses are characterized by a viscous, red-orange surface smear on their rind. It is the complex surface microbiota on the cheese rind that is responsible for the characteristic appearance of this cheese type, but also for the wide range of flavors and textures of the many varieties of smear-ripened cheeses. The surface smear microbiota also represents an important line of defense against the colonization with undesirable microorganisms through various types of interaction, such as competitive exclusion or production of antimicrobial substances. Predominant members of the surface smear microbiota are salt-tolerant yeast and bacteria of the phyla Actinobacteria, Firmicutes, and Proteobacteria. In the past, classical culture-based approaches already shed light on the composition and succession of microorganisms and their individual contribution to the typicity of this cheese type. However, during the last decade, the introduction and application of novel molecular approaches with high-resolution power provided further in-depth analysis and, thus, a much more detailed view of the composition, structure, and diversity of the cheese smear microbiota. This led to abundant novel knowledge, such as the identification of so far unknown community members. Hence, this review is summarizing the current knowledge of the diversity of the surface smear microbiota and its contribution to the quality and safety of smear-ripened cheese. If the succession or composition of the surface-smear microbiota is disturbed, cheese smear defects might occur, which may promote food safety issues. Hence, the discussion of cheese smear defects in the context of an increased understanding of the intricate surface smear ecosystem in this review may not only help in troubleshooting and quality control but also paves the way for innovations that can lead to safer, more consistent, and higher-quality smear-ripened cheeses.

Arthrobacter vasquezii sp. nov., isolated from a soil sample from Union Glacier, Antarctica

A Gram-stain-positive, catalase-positive, non-motile bacteria, with a rod-coccus cycle (designated as EH-1B-1T) was isolated from a soil sample from Union Glacier in Ellsworth Mountains, Antarctica. Strain EH-1B-1T had an optimal growth temperature of 28 °C and grew at pH 7-10. The major cellular fatty acids were anteiso-C15 : 0, iso-C15 : 0, C16 : 0 and anteiso-C17 : 0. The G+C content based on the whole genome sequence was 63.1 mol%. Strain EH-1B-1T was most closely related to members of the genus Arthrobacter, namely Arthrobacter subterraneus and Arthrobacter tumbae. The strain grew on tryptic soy agar, Reasoner's 2A agar, lysogeny broth agar and nutrient agar. The average nucleotide identity and digital DNA-DNA hybridization values between strain EH-1B-1T and its closest reference type strains ranged from 78 to 88 % and from 20.9 to 36.3 %, respectively. Based on phenotypic, chemotypic and genotypic evidence, it is proposed that strain EH-1B-1T represents a novel species of Arthrobacter, for which the name Arthrobacter vasquezii sp. nov. is proposed, with strain EH-1B-1T (RGM 3386T=LMG 32961T) as the type strain.

Structural and functional insights of a cold-adaptive β-glucosidase with very high glucose tolerance from Microbacterium sp. CIAB417

A gene glu1 (WP_243232135.1) coding for β-glucosidase from the genome of Microbacterium sp. CIAB417 was characterized for its cold adaptive nature and tolerance to high levels of glucose and ethanol. The phylogenetic analysis suggested the close association of glu1 with a similar gene from a mesophilic bacterium Microbacterium indicum. The purified recombinant GLU1 displayed its optimal activity and stability at pH 5 and temperature 30ᴼC. Additionally, the presence of L3 loop in GLU1 suggested its cold adaptive nature. The glucose tolerant Gate keeper residues (Leu 174 & Trp 169) with a distance of ∼ 6.953 Å between them was also predicted in GLU1. The GLU1 enzyme showed ≥ 95% and ≥ 40% relative activity in the presence of 5 M glucose and 20% ethanol. The V_max, Km, and K_cat values of GLU1 for cellobiose substrate were observed to be 45.22 U/mg, 3.5 mM, and 41.0157 s^-1, respectively. The GLU1 was found to be highly efficient in hydrolysis of celloologosaccharides (C2-C5), lactose and safranal picrocrocin into glucose. Hence, cold adaptive GLU1 with very high glucose and ethanol tolerance could be very useful in bio-refinery, dairy, and flavor industries.

Involvement of Versatile Bacteria Belonging to the Genus Arthrobacter in Milk and Dairy Products

Milk is naturally a rich source of many essential nutrients; therefore, it is quite a suitable medium for bacterial growth and serves as a reservoir for bacterial contamination. The genus Arthrobacter is a food-related bacterial group commonly present as a contaminant in milk and dairy products as primary and secondary microflora. Arthrobacter bacteria frequently demonstrate the nutritional versatility to degrade different compounds even in extreme environments. As a result of their metabolic diversity, Arthrobacter species have long been of interest to scientists for application in various industry and biotechnology sectors. In the dairy industry, strains from the Arthrobacter genus are part of the microflora of raw milk known as an indicator of hygiene quality. Although they cause spoilage, they are also regarded as important strains responsible for producing fermented milk products, especially cheeses. Several Arthrobacter spp. have reported their significance in the development of cheese color and flavor. Furthermore, based on the data obtained from previous studies about its thermostability, and thermoacidophilic and thermoresistant properties, the genus Arthrobacter promisingly provides advantages for use as a potential producer of β-galactosidases to fulfill commercial requirements as its enzymes allow dairy products to be treated under mild conditions. In light of these beneficial aspects derived from Arthrobacter spp. including pigmentation, flavor formation, and enzyme production, this bacterial genus is potentially important for the dairy industry.

Virulent Phages Isolated from a Smear-Ripened Cheese Are Also Detected in Reservoirs of the Cheese Factory

Smear-ripened cheeses host complex microbial communities that play a crucial role in the ripening process. Although bacteriophages have been frequently isolated from dairy products, their diversity and ecological role in such this type of cheese remain underexplored. In order to fill this gap, the main objective of this study was to isolate and characterize bacteriophages from the rind of a smear-ripened cheese. Thus, viral particles extracted from the cheese rind were tested through a spot assay against a collection of bacteria isolated from the same cheese and identified by sequencing the full-length small subunit ribosomal RNA gene. In total, five virulent bacteriophages infecting Brevibacterium aurantiacum, Glutamicibacter arilaitensis, Leuconostoc falkenbergense and Psychrobacter aquimaris species were obtained. All exhibit a narrow host range, being only able to infect a few cheese-rind isolates within the same species. The complete genome of each phage was sequenced using both Nanopore and Illumina technologies, assembled and annotated. A sequence comparison with known phages revealed that four of them may represent at least new genera. The distribution of the five virulent phages into the dairy-plant environment was also investigated by PCR, and three potential reservoirs were identified. This work provides new knowledge on the cheese rind viral community and an overview of the distribution of phages within a cheese factory.

Arthrobacter terrae sp. nov., a psychrophilic actinobacterium with multi copies of capA gene isolated from Antarctic soil

A Gram-staining-positive, non-spore-forming, non-flagellated, ellipsoidal, strain Z1-20 ^T belonging to the genus Arthrobacter was isolated from a soil sample collected from the Zhongshan station, Antarctic. Phylogenetic analysis of the 16S rRNA gene sequences and phylogenetic analysis revealed that strain Z1-20 ^T formed a unique single cluster in the genus Arthrobacter and shared high 16S rRNA sequence similarities of 97.1% and 96.9% with A. glacialis HLT2-12-2 ^T and A. psychrochitiniphilus GP3^T, respectively. Values of Digital DNA-DNA hybridization (dDDH) between strain Z1-20 ^T against A. glacialis HLT2-12-2 ^T and A. psychrochitiniphilus GP3^T were 20.3% and 13.8%, respectively. Average nucleotide identity (ANI) score between strain Z1-20 ^T against A. glacialis HLT2-12-2 ^T and A. psychrochitiniphilus GP3^T were 72.5% and 72.1%, respectively. Genes for the synthesis of the osmoprotectant glycine betaine and higher copies of capA gene encoding cold shock protein were found in genome of Z1-20 ^T that may help Z1-20 ^T in cold-adaptation. Strain Z1-20 ^T comprised lysine as the diagnostic diamino acid. Based on the results of phylogenetic, phenotypic and chemotaxonomic features, strain Z1-20 ^T represents a novel species of a novel taxon of genus Arthrobacter, for which the name Arthrobacter terrae gen. nov., sp. nov. is proposed.

Identification of Red Pigments Produced by Cheese-Ripening Bacterial Strains of Glutamicibacter arilaitensis Using HPLC

Glutamicibacter arilaitensis is one of the predominant bacterial species involved in the coloration of cheese rinds, especially smear-ripened cheeses. Besides well-known yellow-pigmented carotenoids, this species exhibits an ability to produce red pigments, as the occurrence of pink/red formation was previously found when co-cultured with a fungal strain. In this work, the red pigments synthesized by G. arilaitensis strains grown on cheese-based (curd) solid medium deacidified using Debaryomyces hansenii were identified. The analyses using HPLC equipped with both fluorescence and diode array detectors were performed to characterize the pigments extracted from a dry matter of the medium inoculated with either G. arilaitensis Re117, Po102, or Stp101. Based on the UV–vis absorption spectra, the elution order, and fluorescent property, compared to those of the porphyrin standards, eight metal-free porphyrins, including UPI, UPIII, 7PI, 6PI, 5PI, CPI, CPIII, and MPIX, were indicated as components of the red pigments produced by these G. arilaitensis strains. However, following the chromatographic profiles, the degree of porphyrins formed by each strain was apparently different. Regardless of precise quantitative measurement, the type strains Re117 and Po102 manifested a potential to produce a high amount of CPIII, whereas MPIX was formed by the strains Po102 and Stp101, but exceptionally high by the strain Stp101. The variation in both yield and form of the red pigments synthesized by the cheese-related bacterial G. arilaitensis has not previously been reported; therefore, our results provide the first information on these aspects.

Biological Control and Microbial Ecology Draft Genome Sequence Data of Glutamicibacter sp. FBE-19, a Bacterium Antagonistic to the Plant Pathogen Erwinia tracheiphila

Glutamicibacter sp. FBE-19 was isolated based on its strong antagonism to the cucurbit bacterial blight pathogen Erwinia tracheiphila on plates. Members of the Glutamicibacter genus can promote plant growth under saline conditions and antagonize fungi on plates via chitinolytic activity; however, their production of antibacterial compounds has not been examined. Here, we report the genome sequence of strain FBE-19. The genome is 3.85 Mbp with a G+C content of 60.1% and comprises 3,791 genes. Genes that may contribute to its antagonistic activity include genes for the secondary metabolites stenothricin, salinosporamide A, a second β-lactone compound, and a carotenoid. The Glutamicibacter sp. FBE-19 genome data may be a useful resource if this strain proves to be an effective biocontrol agent against E. tracheiphila.

Enhanced growth and yield of oyster mushroom by growth-promoting bacteria Glutamicibacter arilaitensis MRC119

Promotion of mushroom growth by means of biological agents replacing chemicals is an emerging and highly demanded issue in the sector of mushroom cropping. The present study was aimed to search for a novel bacterium potentially able to enhance mushroom growth and yield. A total of 2165 bacterial isolates purified from different samples were scrutinized through various growth-promoting attributes. As a consequence of rigorous screening, 26 isolates found exhibiting positive traits of mushroom growth promotion. Thereafter, in response to the cocultivation (fungus and bacteria), a potent bacterial strain was isolated capable to improve significantly the mycelial growth. In cocultivation the highest radial and linear growth rate was 7.6 and 8.1 mm/day on 10th and 11th days, respectively. The fruitbody yields and biological efficiency (BE) of the inoculated sets were 28% and 58% higher than the uninoculated control sets. The bacterium was molecularly identified based on 16S ribosomal RNA sequencing and confirmed as Glutamicibacter arilaitensis MRC119. Therefore, the bioinoculant of the current bacterium can be potentially useful as an ecofriendly substitute stimulating the production of mushroom fruit bodies with improved BE.

Arthrobacter bussei sp. nov., a pink-coloured organism isolated from cheese made of cow's milk

A pink-coloured bacterium (strain KR32^T) was isolated from cheese and assigned to the 'Arthrobacter agilis group'. Members of the 'pink Arthrobacter agilis group' form a stable clade (100 % bootstrap value) and contain the species Arthrobacter agilis, Arthrobacter ruber and Arthrobacter echini, which share ≥99.0 % 16S rRNA gene sequence similarity. Isolate KR32^T showed highest 16S rRNA gene sequence similarity (99.9 %) to A. agilis DSM 20550^T. Additional multilocus sequence comparison confirmed the assignment of strain KR32^T to the clade 'pink A. agilis group'. Average nucleotide identity and digital DNA-DNA hybridization values between isolate KR32^T and A. agilis DSM 20550^T were 82.85 and 26.30 %, respectively. The G+C content of the genomic DNA of isolate KR32^T was 69.14 mol%. Chemotaxonomic analysis determined anteiso-C_15 : 0 as the predominant fatty acid and MK-9(H₂) as the predominant menaquinone. Polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and monoacyldimannosyl-monoacylglycerol. The peptidoglycan type of the isolate was A3α. The carotenoid bacterioruberin was detected as the major pigment. At 10 °C, strain KR32^T grew with increased concentrations of bacterioruberin and production of unsaturated fatty acids. Strain KR32^T was a Gram-stain-positive, catalase-positive, oxidase-positive and coccus-shaped bacterium with optimal growth at 27-30 °C and pH 8. The results of phylogenetic and phenotypic analyses enabled the differentiation of the isolate from other closely related species of the 'pink A. agilis group'. Therefore, strain KR32^T represents a novel species for which the name Arthrobacter bussei sp. nov. is proposed. The type strain is KR32^T (=DSM 109896^T=LMG 31480^T=NCCB 100733^T).

Transcriptional Changes on Blight Fruiting Body of Flammulina velutipes Caused by Two New Bacterial Pathogens

A blight disease of Flammulina velutipes was identified with symptoms of growth cessation of young fruiting bodies, short stipe, and brown spots on the pileus. The pathogenic bacteria were identified as Arthrobacter arilaitensis and Pseudomonas yamanorum by Koch's postulate, gram staining, morphological and 16S ribosomal RNA gene sequence analyses. Either of the pathogenic bacteria or both of them can cause the same symptoms. Transcriptome changes in blighted F. velutipes were investigated between diseased and normal samples. Compared to the control group, 1,099 differentially expressed genes (DEGs) were overlapping in the bacteria-infected groups. The DEGs were significantly enriched in pathways such as xenobiotic metabolism by cytochrome P450 and tyrosine metabolism. Based on weighted correlation network analysis (WGCNA), the module most correlated to the pathogen-treated F. velutipes samples and candidate hub genes in the co-regulatory network were identified. Furthermore, a potential diseased mechanism involved in cell wall non-extension, phenolic substrate oxidation, and stress defense response was proposed based on the up-regulation of differentially expressed genes encoding chitin deacetylase, tyrosinase, cytochrome P450, MFS transporter, and clavaminate synthase-like protein. This study provides insights into the underlying reactions of young fruiting body of F. velutipes suffering from blight disease and facilitates the understanding of the pathogenic procedure of bacteriosis in edible mushrooms.

Glutamicibacter mishrai sp. nov., isolated from the coral Favia veroni from Andaman Sea

A novel aerobic marine actinobacterium (strain S5-52^T) belonging to the genus Glutamicibacter was isolated from the coral Favia veroni sampled from the Andaman Sea, India. Cells are Gram stain positive and rod shaped. The DNA G+C content was 58.7 mol%. The major quinones were MK-8 and MK-9. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, glycolipid, trimannosyldiacylglycerol, phospholipid and dimannosylglyceride. The peptidoglycan type was A4α. Strain S5-52^T showed a maximum 16S rRNA similarity of 99.36% with Glutamicibacter halophytocola DSM 101718^T. The genome of strain S5-52^T was 3.57 Mb that contains 3274 protein coding sequences (CDS). DNA-DNA similarity and ANI values between S5-52^T and the reference strains were below 70% and 95-96%, respectively. Analysis of genomic reduction events in the evolutionary path from the LUCA (last universal common ancestor) to G. mishrai LMG 29155^T and G. halophytocola DSM 101718^T exhibit a number of genes involved in amino acid metabolism, cell wall biogenesis and replication, recombination and repair mechanism that reduced in both the species. Based on phenotypic, chemotaxonomic properties and comparative genomic studies, the strain S5-52^T is considered a novel species of the genus Glutamicibacter, for which the name Glutamicibacter mishrai sp. nov. is proposed. The type strain is S5-52^T (= KCTC 39846^T = LMG 29155^T).

Insight Into the Diversity and Possible Role of Plasmids in the Adaptation of Psychrotolerant and Metalotolerant Arthrobacter spp. to Extreme Antarctic Environments

Arthrobacter spp. are coryneform Gram-positive aerobic bacteria, belonging to the class Actinobacteria. Representatives of this genus have mainly been isolated from soil, mud, sludge or sewage, and are usually mesophiles. In recent years, the presence of Arthrobacter spp. was also confirmed in various extreme, including permanently cold, environments. In this study, 36 psychrotolerant and metalotolerant Arthrobacter strains isolated from petroleum-contaminated soil from the King George Island (Antarctica), were screened for the presence of plasmids. The identified replicons were thoroughly characterized in order to assess their diversity and role in the adaptation of Arthrobacter spp. to harsh Antarctic conditions. The screening process identified 11 different plasmids, ranging in size from 8.4 to 90.6 kb. A thorough genomic analysis of these replicons detected the presence of numerous genes encoding proteins that potentially perform roles in adaptive processes such as (i) protection against ultraviolet (UV) radiation, (ii) resistance to heavy metals, (iii) transport and metabolism of organic compounds, (iv) sulfur metabolism, and (v) protection against exogenous DNA. Moreover, 10 of the plasmids carry genetic modules enabling conjugal transfer, which may facilitate their spread among bacteria in Antarctic soil. In addition, transposable elements were identified within the analyzed plasmids. Some of these elements carry passenger genes, which suggests that these replicons may be actively changing, and novel genetic modules of adaptive value could be acquired by transposition events. A comparative genomic analysis of plasmids identified in this study and other available Arthrobacter plasmids was performed. This showed only limited similarities between plasmids of Antarctic Arthrobacter strains and replicons of other, mostly mesophilic, isolates. This indicates that the plasmids identified in this study are novel and unique replicons. In addition, a thorough meta-analysis of 247 plasmids of psychrotolerant bacteria was performed, revealing the important role of these replicons in the adaptation of their hosts to extreme environments.

The Influence of pH, NaCl, and the Deacidifying Yeasts Debaryomyces hansenii and Kluyveromyces marxianus on the Production of Pigments by the Cheese-Ripening Bacteria Arthrobacter arilaitensis

Arthrobacter arilaitensis is a food-related bacterial species under investigation for its involvement in the coloration of surface-ripened cheeses. Presently, information about this species in association with the development of appropriate cheese coloration is still lacking. This study was performed in order to investigate—with the use of spectrocolorimetry—the influence of pH, NaCl, and deacidifying yeasts on the pigmentation of Arthrobacter arilaitensis biofilms. Three types of cheese-based (curd) solid media were prepared by using different deacidification methods: (i) chemical deacidification by NaOH (CM_NaOH); (ii) biological deacidification by the yeast strain Debaryomyces hansenii 304 (CM_Dh304); and (iii) biological deacidification by the yeast strain Kluyveromyces marxianus 44 (CM_Km44). Each medium was prepared with initial pH values of 5.8, 7.0, and 7.5. After pasteurization, agar was incorporated and NaCl was added in varying concentrations (0%, 2%, 4%, and 8% (w/v)). A. arilaitensis Po102 was then inoculated on the so prepared “solid-curd” media, and incubated at 12 °C under light conditions for 28 days. According to the data obtained by spectrocolorimetry in the Compagnie Internationale de l’Eclairage (CIE) L*a*b* color system, all controlled factors appeared to affect the pigments produced by the A. arilaitensis strain. NaCl content in the media showed distinct inhibitory effects on the development of color by this strain when the initial pH was at 5.8. By contrast, when the initial pH of the media was higher (7.0, 7.5), only the highest concentration of NaCl (8%) had this effect, while the coloring capacity of this bacterial species was always higher when D. hansenii 304 was used for deacidification compared to K. marxianus 44.

Microbiota profiling with long amplicons using Nanopore sequencing: full-length 16S rRNA gene and whole rrn operon

Background: Profiling the microbiome of low-biomass samples is challenging for metagenomics since these samples often contain DNA from other sources, such as the host or the environment. The usual approach is sequencing specific hypervariable regions of the 16S rRNA gene, which fails to assign taxonomy to genus and species level. Here, we aim to assess long-amplicon PCR-based approaches for assigning taxonomy at the genus and species level. We use Nanopore sequencing with two different markers: full-length 16S rRNA (~1,500 bp) and the whole rrn operon (16S rRNA-ITS-23S rRNA; 4,500 bp). Methods: We sequenced a clinical isolate of Staphylococcus pseudintermedius, two mock communities (HM-783D, Bei Resources; D6306, ZymoBIOMICS™) and two pools of low-biomass samples (dog skin from either the chin or dorsal back), using the MinION™ sequencer 1D PCR barcoding kit. Sequences were pre-processed, and data were analyzed using the WIMP workflow on EPI2ME or Minimap2 software with rrn database. Results: The full-length 16S rRNA and the rrn operon were used to retrieve the microbiota composition at the genus and species level from the bacterial isolate, mock communities and complex skin samples. For the Staphylococcus pseudintermedius isolate, when using EPI2ME, the amplicons were assigned to the correct bacterial species in ~98% of the cases with the rrn operon marker, and in ~68% of the cases with the 16S rRNA gene. In both skin microbiota samples, we detected many species with an environmental origin. In chin, we found different Pseudomonas species in high abundance, whereas in dorsal skin there were more taxa with lower abundances. Conclusions: Both full-length 16S rRNA and the rrn operon retrieved the microbiota composition of simple and complex microbial communities, even from the low-biomass samples such as dog skin. For an increased resolution at the species level, using the rrn operon would be the best choice.

Microbiota profiling with long amplicons using Nanopore sequencing: full-length 16S rRNA gene and the 16S-ITS-23S of the rrn operon

Background: Profiling the microbiome of low-biomass samples is challenging for metagenomics since these samples are prone to contain DNA from other sources (e.g. host or environment). The usual approach is sequencing short regions of the 16S rRNA gene, which fails to assign taxonomy to genus and species level. To achieve an increased taxonomic resolution, we aim to develop long-amplicon PCR-based approaches using Nanopore sequencing. We assessed two different genetic markers: the full-length 16S rRNA (~1,500 bp) and the 16S-ITS-23S region from the rrn operon (4,300 bp). Methods: We sequenced a clinical isolate of Staphylococcus pseudintermedius, two mock communities and two pools of low-biomass samples (dog skin). Nanopore sequencing was performed on MinION™ using the 1D PCR barcoding kit. Sequences were pre-processed, and data were analyzed using EPI2ME or Minimap2 with rrn database. Consensus sequences of the 16S-ITS-23S genetic marker were obtained using canu. Results: The full-length 16S rRNA and the 16S-ITS-23S region of the rrn operon were used to retrieve the microbiota composition of the samples at the genus and species level. For the Staphylococcus pseudintermedius isolate, the amplicons were assigned to the correct bacterial species in ~98% of the cases with the16S-ITS-23S genetic marker, and in ~68%, with the 16S rRNA gene when using EPI2ME. Using mock communities, we found that the full-length 16S rRNA gene represented better the abundances of a microbial community; whereas, 16S-ITS-23S obtained better resolution at the species level. Finally, we characterized low-biomass skin microbiota samples and detected species with an environmental origin. Conclusions: Both full-length 16S rRNA and the 16S-ITS-23S of the rrn operon retrieved the microbiota composition of simple and complex microbial communities, even from the low-biomass samples such as dog skin. For an increased resolution at the species level, targeting the 16S-ITS-23S of the rrn operon would be the best choice.

Coproporphyrin III Produced by the Bacterium Glutamicibacter arilaitensis Binds Zinc and Is Upregulated by Fungi in Cheese Rinds

Bacterium-fungus interactions play key roles in the assembly of cheese rind microbial communities, but the molecular mechanisms underlying these interactions are poorly characterized. Moreover, millions of people around the world enjoy eating cheeses and cheese rinds, but our understanding of the diversity of microbial metabolites ingested during cheese consumption is limited. The discovery of zinc coproporphyrin III as the cause of pink pigment production by Glutamicibacter arilaitensis suggests that secretion of this molecule is important for microbial acquisition of trace metals.

Microbial communities of fermented food microbiomes typically exhibit predictable patterns of microbial succession. However, the biochemical mechanisms that control the diversity and dynamics of these communities are not well described. Interactions between bacteria and fungi may be one mechanism controlling the development of cheese rind microbiomes. This study characterizes a specific bacterium-fungus interaction previously discovered on cheese rinds between the bacterium Glutamicibacter arilaitensis (formerly Arthrobacter arilaitensis) and fungi of the genus Penicillium and identifies the specialized metabolites produced during cocultures. G. arilaitensis was previously shown to produce an unknown pink pigment in response to the presence of Penicillium. Using a combination of mass spectrometry, nuclear magnetic resonance (NMR), and transcriptome sequencing (RNA-seq), we determined that this pigment production is associated with production of coproporphyrin III. The discovery that coproporphyrin III preferentially bound zinc over other trace metals found in cheese curds highlights the value of using analytical chemistry to confirm identity of predicted chemical species.

IMPORTANCE Bacterium-fungus interactions play key roles in the assembly of cheese rind microbial communities, but the molecular mechanisms underlying these interactions are poorly characterized. Moreover, millions of people around the world enjoy eating cheeses and cheese rinds, but our understanding of the diversity of microbial metabolites ingested during cheese consumption is limited. The discovery of zinc coproporphyrin III as the cause of pink pigment production by Glutamicibacter arilaitensis suggests that secretion of this molecule is important for microbial acquisition of trace metals.

Author Video: An author video summary of this article is available.

Fungal networks shape dynamics of bacterial dispersal and community assembly in cheese rind microbiomes

Most studies of bacterial motility have examined small-scale (micrometer–centimeter) cell dispersal in monocultures. However, bacteria live in multispecies communities, where interactions with other microbes may inhibit or facilitate dispersal. Here, we demonstrate that motile bacteria in cheese rind microbiomes use physical networks created by filamentous fungi for dispersal, and that these interactions can shape microbial community structure. Serratia proteamaculans and other motile cheese rind bacteria disperse on fungal networks by swimming in the liquid layers formed on fungal hyphae. RNA-sequencing, transposon mutagenesis, and comparative genomics identify potential genetic mechanisms, including flagella-mediated motility, that control bacterial dispersal on hyphae. By manipulating fungal networks in experimental communities, we demonstrate that fungal-mediated bacterial dispersal can shift cheese rind microbiome composition by promoting the growth of motile over non-motile community members. Our single-cell to whole-community systems approach highlights the interactive dynamics of bacterial motility in multispecies microbiomes.

Interactions with other microbes may inhibit or facilitate the dispersal of bacteria. Here, Zhang et al. use cheese rind microbiomes as a model to show that physical networks created by filamentous fungi can affect the dispersal of motile bacteria and thus shape the diversity of microbial communities.

Genome Sequence of Arthrobacter antarcticus Strain W2, Isolated from a Slaughterhouse

We report the draft genome sequence of Arthrobacter antarcticus strain W2, which was isolated from a wall of a small slaughterhouse in Denmark. The 4.43-Mb genome sequence was assembled into 170 contigs.

Biodiversity of the Surface Microbial Consortia from Limburger, Reblochon, Livarot, Tilsit, and Gubbeen Cheeses

Comprehensive collaborative studies from our laboratories reveal the extensive biodiversity of the microflora of the surfaces of smear-ripened cheeses. Two thousand five hundred ninety-seven strains of bacteria and 2,446 strains of yeasts from the surface of the smear-ripened cheeses Limburger, Reblochon, Livarot, Tilsit, and Gubbeen, isolated at three or four times during ripening, were identified; 55 species of bacteria and 30 species of yeast were found. The microfloras of the five cheeses showed many similarities but also many differences and interbatch variation. Very few of the commercial smear microorganisms, deliberately inoculated onto the cheese surface, were reisolated and then mainly from the initial stages of ripening, implying that smear cheese production units must have an adventitious "house" flora. Limburger cheese had the simplest microflora, containing two yeasts, Debaryomyces hansenii and Geotrichum candidum, and two bacteria, Arthrobacter arilaitensis and Brevibacterium aurantiacum. The microflora of Livarot was the most complicated, comprising 10 yeasts and 38 bacteria, including many gram-negative organisms. Reblochon also had a very diverse microflora containing 8 yeasts and 13 bacteria (excluding gram-negative organisms which were not identified), while Gubbeen had 7 yeasts and 18 bacteria and Tilsit had 5 yeasts and 9 bacteria. D. hansenii was by far the dominant yeast, followed in order by G. candidum, Candida catenulata, and Kluyveromyces lactis. B. aurantiacum was the dominant bacterium and was found in every batch of the 5 cheeses. The next most common bacteria, in order, were Staphylococcus saprophyticus, A. arilaitensis, Corynebacterium casei, Corynebacterium variabile, and Microbacterium gubbeenense. S. saprophyticus was mainly found in Gubbeen, and A. arilaitensis was found in all cheeses but not in every batch. C. casei was found in most batches of Reblochon, Livarot, Tilsit, and Gubbeen. C. variabile was found in all batches of Gubbeen and Reblochon but in only one batch of Tilsit and in no batch of Limburger or Livarot. Other bacteria were isolated in low numbers from each of the cheeses, suggesting that each of the 5 cheeses has a unique microflora. In Gubbeen cheese, several different strains of the dominant bacteria were present, as determined by pulsed-field gel electrophoresis, and many of the less common bacteria were present as single clones. The culture-independent method, denaturing gradient gel electrophoresis, resulted in identification of several bacteria which were not found by the culture-dependent (isolation and rep-PCR identification) method. It was thus a useful complementary technique to identify other bacteria in the cheeses. The gross composition, the rate of increase in pH, and the indices of proteolysis were different in most of the cheeses.

Review of the taxonomy of the genus Arthrobacter, emendation of the genus Arthrobacter sensu lato, proposal to reclassify selected species of the genus Arthrobacter in the novel genera Glutamicibacter gen. nov., Paeniglutamicibacter gen. nov., Pseudoglutamicibacter gen. nov., Paenarthrobacter gen. nov. and Pseudarthrobacter gen. nov., and emended description of Arthrobacter roseus

In this paper, the taxonomy of the genus Arthrobacter is discussed, from its first description in 1947 to the present state. Emphasis is given to intrageneric phylogeny and chemotaxonomic characteristics, concentrating on quinone systems, peptidoglycan compositions and polar lipid profiles. Internal groups within the genus Arthrobacter indicated from homogeneous chemotaxonomic traits and corresponding to phylogenetic grouping and/or high 16S rRNA gene sequence similarities are highlighted. Furthermore, polar lipid profiles and quinone systems of selected species are shown, filling some gaps concerning these chemotaxonomic traits. Based on phylogenetic groupings, 16S rRNA gene sequence similarities and homogeneity in peptidoglycan types, quinone systems and polar lipid profiles, a description of the genus Arthrobacter sensu lato and an emended description of Arthrobacter roseus are provided. Furthermore, reclassifications of selected species of the genus Arthrobacter into novel genera are proposed, namely Glutamicibacter gen. nov. (nine species), Paeniglutamicibacter gen. nov. (six species), Pseudoglutamicibacter gen. nov. (two species), Paenarthrobacter gen. nov. (six species) and Pseudarthrobacter gen. nov. (ten species).

Arthrobacter endophyticus sp. nov., an endophytic actinobacterium isolated from root of Salsola affinis C. A. Mey

A Gram-staining-positive, white-coloured, aerobic, non-motile, catalase-positive and oxidase-negative, endophytic actinobacterium, designated strain EGI 6500322(T), was isolated from the surface-sterilized root of the halophyte Salsola affinis C. A. Mey collected from Urumqi, Xinjiang province, north-west China. Growth occurred at 5-35 °C (optimum 25-30 °C), at pH 5-10 (optimum pH 7-8) and with 0-13% NaCl (w/v) (optimum 0-5%). The predominant menaquinone was MK-9 (93.1%). The major cellular fatty acids were anteiso-C15:0 (49.5%) and iso-C15:0 (15.1%). The cell-wall peptidoglycan contained lysine, alanine and glutamic acid. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, two unknown phospholipids and one unknown glycolipid. The DNA G+C content of strain EGI 6500322(T) was 62.0 mol%. Based on 16S rRNA gene sequence analysis, the nearest phylogenetic neighbours of strain EGI 6500322(T) were identified as Arthrobacter ardleyensis DSM 17432(T) (98.38%) and Arthrobacter bergerei DSM 16367(T (98.37%). The DNA-DNA relatedness between strain EGI 6500322(T) and Arthrobacter ardleyensis DSM 17432(T) and Arthrobacter bergerei DSM 16367(T) was 53.4 ± 4.1% and 30.5 ± 1.7%, respectively. On the basis of the phylogenetic analysis, chemotaxonomic data, physiological characteristics and DNA-DNA hybridization data, strain EGI 6500322(T) should represent a novel species of the genus Arthrobacter, for which the name Arthrobacter endophyticus sp. nov. is proposed. The type strain is EGI 6500322(T) ( =  CTC 29490(T) = JCM 30091(T)).

Arthrobacter nanjingensis sp. nov., a mineral-weathering bacterium isolated from forest soil

A Gram-stain-positive, non-motile, rod- or coccoid-shaped actinobacterium, designated strain A33T, was isolated from a forest soil sample from Nanjing, Jiangsu Province, PR China. The strain grew optimally at 30 °C, pH 7.0 and with 3 % NaCl (w/v). Phylogenetic analysis of the strain, based on 16S rRNA gene sequences, showed that it was most closely related to Arthrobacter woluwensis (98.4 % sequence similarity), Arthrobacter humicola (97.5 %), Arthrobacter globiformis (97.4 %), Arthrobacter oryzae (97.3 %) and Arthrobacter cupressi (97.0 %). The major cellular fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C15 : 0; MK-9(H2) was the predominant respiratory quinone. The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and three glycolipids. Cell-wall analysis revealed that the peptidoglycan type was A3α, based on l-lysine-l-alanine; the cell-wall sugars were galactose and mannose. The genomic G+C content of strain A33T was 66.8 mol%. The low DNA–DNA relatedness values between strain A33T and recognized species of the genus Arthrobacter and many phenotypic properties supported the classification of strain A33T as a representative of a novel species of the genus Arthrobacter , for which the name Arthrobacter nanjingensis sp. nov. is proposed. The type strain is A33T ( = CCTCC AB 2014069T = DSM 28237T).

Temporal and spatial differences in microbial composition during the manufacture of a continental-type cheese

We sought to determine if the time, within a production day, that a cheese is manufactured has an influence on the microbial community present within that cheese. To facilitate this, 16S rRNA amplicon sequencing was used to elucidate the microbial community dynamics of brine-salted continental-type cheese in cheeses produced early and late in the production day. Differences in the microbial composition of the core and rind of the cheese were also investigated. Throughout ripening, it was apparent that cheeses produced late in the day had a more diverse microbial population than their early equivalents. Spatial variation between the cheese core and rind was also noted in that cheese rinds were initially found to have a more diverse microbial population but thereafter the opposite was the case. Interestingly, the genera Thermus, Pseudoalteromonas, and Bifidobacterium, not routinely associated with a continental-type cheese produced from pasteurized milk, were detected. The significance, if any, of the presence of these genera will require further attention. Ultimately, the use of high-throughput sequencing has facilitated a novel and detailed analysis of the temporal and spatial distribution of microbes in this complex cheese system and established that the period during a production cycle at which a cheese is manufactured can influence its microbial composition.

Isolation and characterization of psychrotolerant endospore-forming Sporosarcina species associated with minced fish meat (surimi)

We studied the changes of resident microbiota in surimi-minced fish meat-during heat-treatment and subsequent cold-storage via the sequencing of partial 16S rRNA gene. Raw surimi made from Alaska pollock, pike conger, and white croaker was contaminated with 10(4) to 10(6)CFU/g of various non-endospore-forming bacteria. Immediately after heat-treatment, the bacterial counts were significantly reduced to less than 1CFU/g, and only endospore-forming bacteria, identified as Bacillus species were retrieved. Subsequently, the bacterial counts increased up to 10 to 10(5)CFU/g in the heated surimi after refrigerated storage at 5 °C for 2 weeks or at 10 °C for 1 week. Most of the isolates from the refrigerated surimi were identified as Sporosarcina species. The Sporosarcina isolates have an increased ability to grow at 10 °C than the isolates related to the other endospore-forming bacteria, such as Bacillus, Lysinibacillus, and Paenibacillus species. Endospores of the Sporosarcina isolates were able to germinate and proliferate in a fish-paste product model system stored at 10 °C within 8 days. In order to study the cold-adaptation mechanism of Sporosarcina species, the fatty acid composition of the isolates was analyzed. At the growth temperature of 10 °C, the proportions of unsaturated to saturated fatty acids and anteiso to iso fatty acids were higher than those at 28 °C. The alteration of the fatty acid composition suggests that Sporosarcina species adapt to cold by maintaining the fluidity of the cell membrane because unsaturated and anteiso fatty acids have lower melting points than saturated and iso fatty acids, respectively. We concluded that the endospores of Sporosarcina species are widely distributed in surimi, and that they can survive heat-treatment and proliferate during cold-storage in fish-paste products. Controlling Sporosarcina species would contribute to improving the quality of surimi product.

Construction of a dairy microbial genome catalog opens new perspectives for the metagenomic analysis of dairy fermented products

Background

Microbial communities of traditional cheeses are complex and insufficiently characterized. The origin, safety and functional role in cheese making of these microbial communities are still not well understood. Metagenomic analysis of these communities by high throughput shotgun sequencing is a promising approach to characterize their genomic and functional profiles. Such analyses, however, critically depend on the availability of appropriate reference genome databases against which the sequencing reads can be aligned.

Results

We built a reference genome catalog suitable for short read metagenomic analysis using a low-cost sequencing strategy. We selected 142 bacteria isolated from dairy products belonging to 137 different species and 67 genera, and succeeded to reconstruct the draft genome of 117 of them at a standard or high quality level, including isolates from the genera Kluyvera, Luteococcus and Marinilactibacillus, still missing from public database. To demonstrate the potential of this catalog, we analysed the microbial composition of the surface of two smear cheeses and one blue-veined cheese, and showed that a significant part of the microbiota of these traditional cheeses was composed of microorganisms newly sequenced in our study.

Conclusions

Our study provides data, which combined with publicly available genome references, represents the most expansive catalog to date of cheese-associated bacteria. Using this extended dairy catalog, we revealed the presence in traditional cheese of dominant microorganisms not deliberately inoculated, mainly Gram-negative genera such as Pseudoalteromonas haloplanktis or Psychrobacter immobilis, that may contribute to the characteristics of cheese produced through traditional methods.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1101) contains supplementary material, which is available to authorized users.

Traditional cheeses: rich and diverse microbiota with associated benefits

The risks and benefits of traditional cheeses, mainly raw milk cheeses, are rarely set out objectively, whence the recurrent confused debate over their pros and cons. This review starts by emphasizing the particularities of the microbiota in traditional cheeses. It then describes the sensory, hygiene, and possible health benefits associated with traditional cheeses. The microbial diversity underlying the benefits of raw milk cheese depends on both the milk microbiota and on traditional practices, including inoculation practices. Traditional know-how from farming to cheese processing helps to maintain both the richness of the microbiota in individual cheeses and the diversity between cheeses throughout processing. All in all more than 400 species of lactic acid bacteria, Gram and catalase-positive bacteria, Gram-negative bacteria, yeasts and moulds have been detected in raw milk. This biodiversity decreases in cheese cores, where a small number of lactic acid bacteria species are numerically dominant, but persists on the cheese surfaces, which harbour numerous species of bacteria, yeasts and moulds. Diversity between cheeses is due particularly to wide variations in the dynamics of the same species in different cheeses. Flavour is more intense and rich in raw milk cheeses than in processed ones. This is mainly because an abundant native microbiota can express in raw milk cheeses, which is not the case in cheeses made from pasteurized or microfiltered milk. Compared to commercial strains, indigenous lactic acid bacteria isolated from milk/cheese, and surface bacteria and yeasts isolated from traditional brines, were associated with more complex volatile profiles and higher scores for some sensorial attributes. The ability of traditional cheeses to combat pathogens is related more to native antipathogenic strains or microbial consortia than to natural non-microbial inhibitor(s) from milk. Quite different native microbiota can protect against Listeria monocytogenes in cheeses (in both core and surface) and on the wooden surfaces of traditional equipment. The inhibition seems to be associated with their qualitative and quantitative composition rather than with their degree of diversity. The inhibitory mechanisms are not well elucidated. Both cross-sectional and cohort studies have evidenced a strong association of raw-milk consumption with protection against allergic/atopic diseases; further studies are needed to determine whether such association extends to traditional raw-milk cheese consumption. In the future, the use of meta-omics methods should help to decipher how traditional cheese ecosystems form and function, opening the way to new methods of risk-benefit management from farm to ripened cheese.

Draft Genome Sequence of Arthrobacter crystallopoietes Strain BAB-32, Revealing Genes for Bioremediation

Arthrobacter crystallopoietes strain BAB-32, a Gram-positive obligate aerobic actinobacterium having potential application in bioremediation and bioreduction of a few metals, was isolated from rhizosphere soil of Gandhinagar, Gujarat, India. The draft genome (4.3 Mb) of the strain revealed a few vital gene clusters involved in the metabolism of aromatic compounds, zinc, and sulfur.

Complete genome sequence of Corynebacterium variabile DSM 44702 isolated from the surface of smear-ripened cheeses and insights into cheese ripening and flavor generation

Background

Corynebacterium variabile is part of the complex microflora on the surface of smear-ripened cheeses and contributes to the development of flavor and textural properties during cheese ripening. Still little is known about the metabolic processes and microbial interactions during the production of smear-ripened cheeses. Therefore, the gene repertoire contributing to the lifestyle of the cheese isolate C. variabile DSM 44702 was deduced from the complete genome sequence to get a better understanding of this industrial process.

Results

The chromosome of C. variabile DSM 44702 is composed of 3, 433, 007 bp and contains 3, 071 protein-coding regions. A comparative analysis of this gene repertoire with that of other corynebacteria detected 1, 534 predicted genes to be specific for the cheese isolate. These genes might contribute to distinct metabolic capabilities of C. variabile, as several of them are associated with metabolic functions in cheese habitats by playing roles in the utilization of alternative carbon and sulphur sources, in amino acid metabolism, and fatty acid degradation. Relevant C. variabile genes confer the capability to catabolize gluconate, lactate, propionate, taurine, and gamma-aminobutyric acid and to utilize external caseins. In addition, C. variabile is equipped with several siderophore biosynthesis gene clusters for iron acquisition and an exceptional repertoire of AraC-regulated iron uptake systems. Moreover, C. variabile can produce acetoin, butanediol, and methanethiol, which are important flavor compounds in smear-ripened cheeses.

Conclusions

The genome sequence of C. variabile provides detailed insights into the distinct metabolic features of this bacterium, implying a strong adaption to the iron-depleted cheese surface habitat. By combining in silico data obtained from the genome annotation with previous experimental knowledge, occasional observations on genes that are involved in the complex metabolic capacity of C. variabile were integrated into a global view on the lifestyle of this species.

Arthrobacter livingstonensis sp. nov. and Arthrobacter cryotolerans sp. nov., salt-tolerant and psychrotolerant species from Antarctic soil

Two novel cold-tolerant, Gram-stain-positive, motile, facultatively anaerobic bacterial strains, LI2T and LI3T, were isolated from moss-covered soil from Livingston Island, Antarctica, near the Bulgarian station St Kliment Ohridski. A rod–coccus cycle was observed for both strains. 16S rRNA gene sequence analysis revealed an affiliation to the genus Arthrobacter, with the highest similarity to Arthrobacter stackebrandtii and Arthrobacter psychrochitiniphilus for strain LI2T (97.8 and 97.7 % similarity to the respective type strains) and to Arthrobacter kerguelensis and Arthrobacter psychrophenolicus for strain LI3T (97.4 and 97.3 % similarity to the respective type strains). The growth temperature range was −6 to 28 °C for LI2T and −6 to 24 °C for LI3T, with an optimum at 16 °C for both strains. Growth occurred at 0–10 % (w/v) NaCl, with optimum growth at 0–1 % (w/v) for LI2T and 0.5–3 % (w/v) for LI3T. The pH range for growth was pH 4–9.5 with an optimum of pH 8 for LI2T and pH 6.5 for LI3T. The predominant fatty acids were anteiso-C15 : 0, C18 : 0 and anteiso-C17 : 0 for LI2T and anteiso-C15 : 0 and C18 : 0 for LI3T. Physiological and biochemical tests clearly differentiated strain LI2T from A. stackebrandtii and A. psychrochitiniphilus and strain LI3T from A. kerguelensis and A. psychrophenolicus. Therefore, two novel species within the genus Arthrobacter are proposed: Arthrobacter livingstonensis sp. nov. (type strain LI2T  = DSM 22825T  = NCCB 100314T) and Arthrobacter cryotolerans sp. nov. (type strain LI3T  = DSM 22826T  = NCCB 100315T).

The arthrobacter arilaitensis Re117 genome sequence reveals its genetic adaptation to the surface of cheese

Arthrobacter arilaitensis is one of the major bacterial species found at the surface of cheeses, especially in smear-ripened cheeses, where it contributes to the typical colour, flavour and texture properties of the final product. The A. arilaitensis Re117 genome is composed of a 3,859,257 bp chromosome and two plasmids of 50,407 and 8,528 bp. The chromosome shares large regions of synteny with the chromosomes of three environmental Arthrobacter strains for which genome sequences are available: A. aurescens TC1, A. chlorophenolicus A6 and Arthrobacter sp. FB24. In contrast however, 4.92% of the A. arilaitensis chromosome is composed of ISs elements, a portion that is at least 15 fold higher than for the other Arthrobacter strains. Comparative genomic analyses reveal an extensive loss of genes associated with catabolic activities, presumably as a result of adaptation to the properties of the cheese surface habitat. Like the environmental Arthrobacter strains, A. arilaitensis Re117 is well-equipped with enzymes required for the catabolism of major carbon substrates present at cheese surfaces such as fatty acids, amino acids and lactic acid. However, A. arilaitensis has several specificities which seem to be linked to its adaptation to its particular niche. These include the ability to catabolize D-galactonate, a high number of glycine betaine and related osmolyte transporters, two siderophore biosynthesis gene clusters and a high number of Fe(3+)/siderophore transport systems. In model cheese experiments, addition of small amounts of iron strongly stimulated the growth of A. arilaitensis, indicating that cheese is a highly iron-restricted medium. We suggest that there is a strong selective pressure at the surface of cheese for strains with efficient iron acquisition and salt-tolerance systems together with abilities to catabolize substrates such as lactic acid, lipids and amino acids.

The type of cheese curds determined the colouring capacity of Brevibacterium and Arthrobacter species

This study compares the colouring capacity of Brevibacterium aurantiacum (BA), Brevibacterium BL and Arthrobacter species AS in relation to deacidified media made from lactic curd (Epoisses), mixed curds (Munster) and rennet curds (Livarot or Reblochon). BA colouring capacity proved to be constant, leading to a dark orange colour, irrespective of the deacidified media. However, it gave too dark a colour for Reblochon. The strains BL and AS were not adapted to the colouring of Epoisses deacidified medium. On the Livarot or Munster deacidified medium, these two strains provided a light yellow orange colour range that was not suitable for these cheeses. However, these two strains (BL and AS) produced a suitable colour for Reblochon deacidified medium.

Arthrobacter antarcticus sp. nov., isolated from an Antarctic marine sediment

A bacterial strain, SPC26(T), was isolated from a sediment sample of the Southern Ocean off Antarctica. The strain was Gram-staining- and catalase-positive and contained lysine and alanine in the cell-wall peptidoglycan. The major cellular fatty acids were anteiso-C₁₅:₀ (54.92 %), iso-C₁₅:₀ (11.47 %), anteiso-C₁₇:₀ (6.48 %) and anteiso-C₁₅:₁ (6.38 %) and the major menaquinones were MK-8, MK-9 and MK-10. The major polar lipids were phosphatidylethanolamine and diphosphatidylglycerol. The G+C content was 68 ± 0.5 mol%. Based on 16S rRNA gene sequence similarities, the nearest phylogenetic neighbours of strain SPC26(T) were identified as Arthrobacter gangotriensis Lz1y(T) (98.8 %), A. sulfureus DSM 20167(T) (98.6 %), A. psychrophenolicus DSM 15454(T) (97.9 %) and A. kerguelensis KGN15(T) (97.5). With these strains, strain SPC26(T) exhibited DNA-DNA relatedness values of 36, 21, 12 and 10 %, respectively. Therefore, on the basis of 16S rRNA gene sequence comparisons, phylogenetic analysis, phenotypic characteristics and DNA-DNA relatedness, it is proposed that strain SPC26(T) represents a novel species of Arthrobacter, for which the name Arthrobacter antarcticus sp. nov. is proposed, with strain SPC26(T) (=LMG 24542(T) =NCCB 100228(T)) as the type strain.

Stability of the biodiversity of the surface consortia of Gubbeen, a red-smear cheese

A total of 1,052 bacteria and 828 yeasts were isolated from the surface flora of 6 batches of Gubbeen cheese made in 1996-1997 and 2002-2003. Stability of the microflora was evaluated over time and also during ripening at 4, 10, and 16 d (batches 4, 5, and 6) or at 4, 16, 23, and 37 d (batches 1, 2, and 3). Bacteria were identified using pulsed-field gel electrophoresis, repetitive extragenic palindromic-PCR, and 16S rRNA gene sequencing, and yeasts were identified by Fourier transform infrared spectroscopy. The bacteria included at least 17 species, of which the most common were Staphylococcus saprophyticus (316 isolates), Corynebacterium casei (248 isolates), Brevibacterium aurantiacum (187 isolates), Corynebacterium variabile (146 isolates), Microbacterium gubbeenense (55 isolates), Staphylococcus equorum/cohnii (31 isolates), and Psychrobacter spp. (26 isolates). The most common yeasts were Debaryomyces hansenii (624 isolates), Candida catenulata (135 isolates), and Candida lusitaniae (62 isolates). In all batches of cheese except batch 2, a progression of bacteria was observed, with staphylococci dominating the early stages of ripening and coryneforms the later stages. No progression of yeast was found. Pulsed-field gel electrophoresis showed that several different strains of the 5 important species of bacteria were present, but generally only one predominated. The commercial strains used for smearing the cheese were recovered, but only in very small numbers early in ripening. Four species, B. aurantiacum, C. casei, C. variabile, and Staph. saprophyticus, were found on all batches of cheese, but their relative importance varied considerably. The results imply that significant variation occurs in the surface microflora of cheese.

Commercial ripening starter microorganisms inoculated into cheese milk do not successfully establish themselves in the resident microbial ripening consortia of a South german red smear cheese

Production of smear-ripened cheese critically depends on the surface growth of multispecies microbial consortia comprising bacteria and yeasts. These microorganisms often originate from the cheese-making facility and, over many years, have developed into rather stable, dairy-specific associations. While commercial smear starters are frequently used, it is unclear to what degree these are able to establish successfully within the resident microbial consortia. Thus, the fate of the smear starters of a German Limburger cheese subjected to the "old-young" smearing technique was investigated during ripening. The cheese milk was supplemented with a commercial smear starter culture containing Debaryomyces hansenii, Galactomyces geotrichum, Arthrobacter arilaitensis, and Brevibacterium aurantiacum. Additionally, the cheese surface was inoculated with an extremely stable in-house microbial consortium. A total of 1,114 yeast and 1,201 bacterial isolates were identified and differentiated by Fourier transform infrared spectroscopy. Furthermore, mitochondrial DNA restriction fragment length polymorphism, random amplified polymorphic DNA, repetitive PCR, and pulsed field gel electrophoresis analyses were used to type selected isolates below the species level. The D. hansenii starter strain was primarily found early in the ripening process. The G. geotrichum starter strain in particular established itself after relocation to a new ripening room. Otherwise, it occurred at low frequencies. The bacterial smear starters could not be reisolated from the cheese surface at all. It is concluded that none of the smear starter strains were able to compete significantly and in a stable fashion against the resident microbial consortia, a result which might have been linked to the method of application. This finding raises the issue of whether addition of starter microorganisms during production of this type of cheese is actually necessary.

Microbial interactions within a cheese microbial community

The interactions that occur during the ripening of smear cheeses are not well understood. Yeast-yeast interactions and yeast-bacterium interactions were investigated within a microbial community composed of three yeasts and six bacteria found in cheese. The growth dynamics of this community was precisely described during the ripening of a model cheese, and the Lotka-Volterra model was used to evaluate species interactions. Subsequently, the effects on ecosystem functioning of yeast omissions in the microbial community were evaluated. It was found both in the Lotka-Volterra model and in the omission study that negative interactions occurred between yeasts. Yarrowia lipolytica inhibited mycelial expansion of Geotrichum candidum, whereas Y. lipolytica and G. candidum inhibited Debaryomyces hansenii cell viability during the stationary phase. However, the mechanisms involved in these interactions remain unclear. It was also shown that yeast-bacterium interactions played a significant role in the establishment of this multispecies ecosystem on the cheese surface. Yeasts were key species in bacterial development, but their influences on the bacteria differed. It appeared that the growth of Arthrobacter arilaitensis or Hafnia alvei relied less on a specific yeast function because these species dominated the bacterial flora, regardless of which yeasts were present in the ecosystem. For other bacteria, such as Leucobacter sp. or Brevibacterium aurantiacum, growth relied on a specific yeast, i.e., G. candidum. Furthermore, B. aurantiacum, Corynebacterium casei, and Staphylococcus xylosus showed reduced colonization capacities in comparison with the other bacteria in this model cheese. Bacterium-bacterium interactions could not be clearly identified.

Growth characteristics of Brevibacterium, Corynebacterium, Microbacterium, and Staphylococcus spp. isolated from surface-ripened cheese

The growth characteristics of five bacteria, Brevibacterium aurantiacum 1-16-58, Corynebacterium casei DPC 5298(T), Corynebacterium variabile DPC 5310, Microbacterium gubbeenense DPC 5286(T), and Staphylococcus saprophyticus 4E61, all of which were isolated from the surface of smear cheese, were studied in complex and chemically defined media. All of the coryneforms, except M. gubbeenense, grew in 12% salt, while B. aurantiacum and S. saprophyticus grew in 15% salt. All five bacteria assimilated lactate in a semisynthetic medium, and none of the coryneform bacteria assimilated lactose. Glucose assimilation was poor, except by S. saprophyticus and C. casei. Five to seven amino acids were assimilated by the coryneforms and 12 by S. saprophyticus. Glutamate, phenylalanine, and proline were utilized by all five bacteria, whereas utilization of serine, threonine, aspartate, histidine, alanine, arginine, leucine, isoleucine, and glycine depended on the organism. Growth of C. casei restarted after addition of glutamate, proline, serine, and lactate at the end of the exponential phase, indicating that these amino acids and lactate can be used as energy sources. Pantothenic acid was essential for the growth of C. casei and M. gubbeenense. Omission of biotin reduced the growth of B. aurantiacum, C. casei, and M. gubbeenense. All of the bacteria contained lactate dehydrogenase activity (with both pyruvate and lactate as substrates) and glutamate pyruvate transaminase activity but not urease activity.

Zhihengliuella halotolerans gen. nov., sp. nov., a novel member of the family Micrococcaceae

The actinobacterial strain YIM 70185T was isolated from a saline soil sample collected from Qinghai province, north-west China, and subjected to a taxonomic investigation. Phylogenetic analysis based on 16S rRNA gene sequences revealed 93.5–96.4 % similarity to members of related genera in the family Micrococcaceae. In the phylogenetic dendrogram based on 16S rRNA gene sequence analysis, strain YIM 70185T formed a separate clade next to the genera Micrococcus and Citricoccus within the family Micrococcaceae. The peptidoglycan type was A4α, l-lys–l-ala–l-Glu. Cell-wall sugars contained glucose and tyvelose. The polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, an unknown phospholipid and an unknown glycolipid. The menaquinones were MK-9, MK-10 and MK-8 (molar ratio 5 : 2 : 1). The major fatty acids were ai-C15 : 0 and i-C15 : 0 and the DNA G+C content was 66.5 mol%. These chemotaxonomic profiles supported the assignment of strain YIM 70185T to a novel genus within the family Micrococcaceae. The name Zhihengliuella halotolerans gen. nov., sp. nov. is proposed. The type strain of Zhihengliuella halotolerans is YIM 70185T (=DSM 17364T=KCTC 19085T).

Sources of the adventitious microflora of a smear-ripened cheese

AIMS

To determine the relationships between the major organisms from the cheese-making personnel and environment and the surface of a smear cheese.

METHODS AND RESULTS

360 yeast and 593 bacteria from the cheese surface, the dairy environment and the hands and arms of personnel were collected. Pulsed-field gel electrophoresis, repetitive sequence-based polymerase chain reaction and 16S rDNA sequencing were used for typing and identifying the bacteria, and mitochondrial DNA restriction fragment length polymorphism and Fourier-transform infrared spectroscopy for typing and identifying the yeast. The three most dominant bacteria were Corynebacterium casei, Corynebacterium variabile and Staphylococcus saprophyticus, which were divided into three, five and seven clusters, respectively, by macrorestriction analysis. The same clones from these organisms were isolated on the cheese surface, the dairy environment and the skin of the cheese personnel. Debaryomyces hansenii was the most dominant yeast.

CONCLUSIONS

A 'house' microflora exists in the cheese plant. Although the original source of the micro-organisms was not identified, the brines were an important source of S. saprophyticus and D. hansenii and, additionally, the arms and hands of the workers the sources of C. casei and C. variabile.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first time that the major contribution of the house microflora to the ripening of a smear-ripened cheese has been demonstrated.

Agrococcus casei sp. nov., isolated from the surfaces of smear-ripened cheeses

Seven Gram-positive, coryneform bacteria with virtually identical whole-organism protein patterns were isolated from the surface of smear-ripened cheeses. Representatives of these strains were the subject of a polyphasic study designed to establish their taxonomic status. The organisms formed a distinct branch in the Microbacteriaceae 16S rRNA gene tree and were most closely related to members of the genus Agrococcus, sharing sequence similarities of 95.4–98.7 %. The chemotaxonomic profiles of the strains were consistent with their classification in the genus Agrococcus. The combined genotypic and phenotypic data show that the isolates should be classified in the genus Agrococcus as representatives of a novel species. The name Agrococcus casei sp. nov. is proposed for this taxon. Isolate R-17892t2T (=DSM 18061T=LMG 22410T) is the type strain of Agrococcus casei sp. nov.

Quantitative detection of Corynebacterium casei in cheese by real-time PCR

The flora on the surface of smear-ripened cheeses is composed of numerous species of bacteria and yeasts that contribute to the production of the desired organoleptic properties. Due to the absence of selective media, it is very difficult to quantify cheese surface bacteria, and, consequently, the ecology of the cheese surface microflora has not been extensively investigated. We developed a SYBR green I real-time PCR method to quantify Corynebacterium casei, a major species of smear-ripened cheeses, using primers designed to target the 16S rRNA gene. It was possible to recover C. casei genomic DNA from the cheese matrix with nearly the same yield that C. casei genomic DNA is recovered from cells recovered by centrifugation from liquid cultures. Quantification was linear over a range from 10(5) to 10(10) CFU per g of cheese. The specificity of the assay was demonstrated with DNA from species related to C. casei and from other bacteria and yeasts belonging to the cheese flora. Nine commercial cheeses were analyzed by real-time PCR, and six of them were found to contain more than 10(5) CFU equivalents of C. casei per g. In two of them, the proportion of C. casei in the total bacterial flora was nearly 40%. The presence of C. casei in these samples was further confirmed by single-strand conformation polymorphism analysis and by a combined approach consisting of plate counting and 16S rRNA gene sequencing. We concluded that SYBR green I real-time PCR may be used as a reliable species-specific method for quantification of bacteria from the surface of cheeses.

Survival of surface ripening cultures during storage and monitoring their development on cheese

AIMS

To study the survival of bacteria isolated from the surface of smear cheese and monitor their development during cheese ripening.

METHODS AND RESULTS

The storage of five potential bacterial surface-ripening cheese cultures, Brevibacterium aurantiacum, Corynebacterium casei, Corynebacterium variable, Microbacterium gubbeenense and Staphylococcus saprophyticus, in maximum recovery diluent (MRD), containing 0.85% w/v or 5% w/v NaCl, at 21 or 4 degrees C for 40 days, was investigated. All five strains studied survived well with a maximum decrease of c. 2.5 log(10) CFU ml(-1) after storage for 40 days at 4 degrees C in 0.85% or 5% w/v NaCl. Survival, especially of C. variable, was less at 21 degrees C. The development of defined ripening cultures containing C. casei and Debaryomyces hansenii on two farmhouse cheeses was also evaluated. Using pulsed-field gel electrophoresis (PFGE) for the bacteria and mitochondrial DNA restriction fragment length polymorphism (mtDNA-RFLP) for the yeast, it was shown that the ripening cultures could be re-isolated in high numbers, 10(8) CFU cm(-2) for C. casei and 10(6) CFU cm(-2) for D. hansenii, from the cheese surface after 2.5 weeks of ripening.

CONCLUSIONS

Ripening strains of surface ripening cultures can be stored in MRD containing 5% w/v salt at 4 degrees C for at least 40 days. Such cultures are recovered in high numbers from the cheese during ripening.

SIGNIFICANCE AND IMPACT OF STUDY

This study has provided a low-cost and efficient way to store bacteria that could be used as ripening cultures for smear cheese. Such cultures can be recovered in high numbers from the cheese surface during ripening.