Production of carotenoids by Arthrobacter arilaitensis strains isolated from smear-ripened cheeses

Deciphering Rind Color Heterogeneity of Smear-Ripened Munster Cheese and Its Association with Microbiota

Color is one of the first criteria to assess the quality of cheese. However, very limited data are available on the color heterogeneity of the rind and its relationship with microbial community structure. In this study, the color of a wide range of smear-ripened Munster cheeses from various origins was monitored during storage by photographic imaging and data analysis in the CIELAB color space using luminance, chroma, and hue angle as descriptors. Different levels of inter- and intra-cheese heterogeneity were observed. The most heterogeneous Munster cheeses were the darkest with orange-red colors. The most homogeneous were the brightest with yellow-orange. K-means clustering revealed three clusters distinguished by their color heterogeneity. Color analysis coupled with metabarcoding showed that rinds with heterogeneous color exhibited higher microbial diversity associated with important changes in their microbial community structure during storage. In addition, intra-cheese community structure fluctuations were associated with heterogeneity in rind color. The species Glutamicibacter arilaitensis and Psychrobacter nivimaris/piscatorii were found to be positively associated with the presence of undesirable brown patches. This study highlights the close relationship between the heterogeneity of the cheese rind and its microbiota.

Investigation of Freezing and Freeze-Drying for Preserving and Re-Using a Whole Microbial Cheese Community

Preserving microbial ecosystems obtained from traditional cheese-making processes is crucial to safeguarding the biodiversity of microbial cheese communities and thus ensuring that the high flavor quality of traditional cheeses is maintained. Few protocols have been proposed for the long-term storage of microbial consortia. This work aimed to develop preservation methods to stabilize the entire microbial community in smear-ripened cheese without multiplication or isolation. A simplified microbial community, capable of reproducing the metabolic pattern of cheese maturation, was used in three independent cheese productions. Cheese samples were taken before and after the ripening step, mixed with maltodextrin or saline solution, and subjected to different stabilization conditions including freezing and freeze-drying, followed by 1 month of storage. Microbial survival was quantified using the colony-forming unit assay. Differential scanning calorimetry was used to relate the physical events occurring within the samples to the microbial storage stability. Freezing at -80 °C resulted in the lowest loss of culturability (<0.8 log unit), followed by freezing at -20 °C and freeze-drying. The ripening bacteria appeared as the most sensitive microorganisms within the community. Moreover, a successful cheese production using the best-stabilized community showed the possibility of preserving and re-using an entire microbial community of interest.

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.

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.

Arthrobacter wenxiniae sp. nov., a novel plant growth-promoting rhizobacteria species harbouring a carotenoids biosynthetic gene cluster

A bacterial strain, designated AETb3-4^T was isolated from the rhizosphere of lily. Comparison of 16S rRNA gene sequences showed that the sequence from strain AETb3-4^T exhibits high sequence similarity with those of Arthrobacter silviterrae KIS14-16^T (97.9%), Arthrobacter livingstonensis LI2^T (97.2%) and Arthrobacter stackebrandtii CCM 2783^T (97.0%). Whole genome average nucleotide identity (ANI) and the digital DNA-DNA hybridization (dDDH) values between strain AETb3-4T and the reference strains A. silviterrae DSM 27180^T, A. livingstonensis L12^T and A. stackebrandtii DSM 16005^T were below 83.6% and 27.7%, respectively, values which are considerably below the proposed thresholds for the species delineation, consistent with the proposal that strain AETb3-4^T represents a novel species. The genome size of strain AETb3-4^T is 4.33 Mb and the genomic DNA G + C content is 67.3%. The main polar lipids were identified as phosphatidylglycerol, diphosphatidylglycero, phosphatidylinositol and an unidentified glycolipid. The major fatty acids (> 10%) were identified as anteiso-C_{15: 0} and anteiso-C_{17: 0}. The predominant menaquinone was found to be menaquinone 9 (MK-9) (H₂) (82.2%). Phenotypic tests allowed the strain to be differentiated from its close phylogenetic neighbors. Based on the results obtained, it is proposed that the strain AETb3-4^T (= CFCC 16390^T = LMG 31708^T) represents a novel species in the genus Arthrobacter, for which the names Arthrobacter wenxiniae sp. nov. is proposed. In addition, the novel strain AETb3-4^T has multiple plant growth-promoting characters including ACC-deaminase activity and production of IAA. Furthermore, the genome contains secondary metabolite biosynthesis gene clusters, including a carotenoid biosynthetic gene cluster, suggesting potential capacities for secondary metabolite synthesis. These data suggest that strain AETb3-4^T may have potential applications both in medicine and sustainable agriculture.

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.

Isolation and characterization of a heavy metal- and antibiotic-tolerant novel bacterial strain from a contaminated culture plate of Chlamydomonas reinhardtii, a green micro-alga

Background:Chlamydomonas reinhardtii, a green micro-alga, is normally cultured in laboratories in Tris-Acetate Phosphate (TAP), a medium which contains acetate as the sole carbon source. Acetate in TAP can lead to occasional bacterial and fungal contamination. We isolated a yellow-pigmented bacterium from a Chlamydomonas TAP plate. It was named Clip185 based on the Chlamydomonas strain plate it was isolated from. In this article we present our work on the isolation, taxonomic identification and physiological and biochemical characterizations of Clip185. Methods: We measured sensitivities of Clip185 to five antibiotics and performed standard microbiological tests to characterize it. We partially sequenced the 16S rRNA gene of Clip185. We identified the yellow pigment of Clip185 by spectrophotometric analyses. We tested tolerance of Clip185 to six heavy metals by monitoring its growth on Lysogeny Broth (LB) media plates containing 0.5 mM -10 mM concentrations of six different heavy metals. Results: Clip185 is an aerobic, gram-positive rod, oxidase-negative, mesophilic, alpha-hemolytic bacterium. It can ferment glucose, sucrose and mannitol. It is starch hydrolysis-positive. It is very sensitive to vancomycin but resistant to penicillin and other bacterial cell membrane- and protein synthesis-disrupting antibiotics. Clip185 produces a C50 carotenoid, decaprenoxanthin, which is a powerful anti-oxidant with a commercial demand. Decaprenoxanthin production is induced in Clip185 under light. NCBI-BLAST analyses of the partial 16S rRNA gene sequence of Clip185 revealed a 99% sequence identity to that of Microbacterium binotii strain PK1-12M and Microbacterium sp. strain MDP6. Clip185 is able to tolerate toxic concentrations of six heavy metals. Conclusions: Our results show that Clip185 belongs to the genus Microbacterium. In the future, whole genome sequencing of Clip185 will clarify if Clip185 is a new Microbacterium species or a novel strain of Microbacterium binotii, and will reveal its genes involved in antibiotic-resistance, heavy-metal tolerance and regulation of decaprenoxanthin biosynthesis.

Isolation and characterization of a heavy metal- and antibiotic-tolerant novel bacterial strain from a contaminated culture plate of Chlamydomonas reinhardtii, a green micro-alga

Background:Chlamydomonas reinhardtii, a green micro-alga, is normally cultured in laboratories in Tris-Acetate Phosphate (TAP), a medium which contains acetate as the sole carbon source. Acetate in TAP can lead to occasional bacterial and fungal contamination. We isolated a yellow-pigmented bacterium from a Chlamydomonas TAP plate. It was named Clip185 based on the Chlamydomonas strain plate it was isolated from. In this article we present our work on the isolation, taxonomic identification and physiological and biochemical characterizations of Clip185. Methods: We measured sensitivities of Clip185 to five antibiotics and performed standard microbiological tests to characterize it. We partially sequenced the 16S rRNA gene of Clip185. We identified the yellow pigment of Clip185 by spectrophotometric analyses. We tested tolerance of Clip185 to six heavy metals by monitoring its growth on Lysogeny Broth (LB) media plates containing 0.5 mM -10 mM concentrations of six different heavy metals. Results: Clip185 is an aerobic, gram-positive rod, oxidase-negative, mesophilic, alpha-hemolytic bacterium. It can ferment glucose, sucrose and mannitol. It is starch hydrolysis-positive. It is very sensitive to vancomycin but resistant to penicillin and other bacterial cell membrane- and protein synthesis-disrupting antibiotics. Clip185 produces a C50 carotenoid, decaprenoxanthin, which is a powerful anti-oxidant with a commercial demand. Decaprenoxanthin production is induced in Clip185 under light. NCBI-BLAST analyses of the partial 16S rRNA gene sequence of Clip185 revealed a 99% sequence identity to that of Microbacterium binotii strain PK1-12M and Microbacterium sp. strain MDP6. Clip185 is able to tolerate toxic concentrations of six heavy metals. Conclusions: Our results show that Clip185 belongs to the genus Microbacterium. In the future, whole genome sequencing of Clip185 will clarify if Clip185 is a new Microbacterium species or a novel strain of Microbacterium binotii, and will reveal its genes involved in antibiotic-resistance, heavy-metal tolerance and regulation of decaprenoxanthin biosynthesis.

A comprehensive review on carotenoids in foods and feeds: status quo, applications, patents, and research needs

Carotenoids are isoprenoids widely distributed in foods that have been always part of the diet of humans. Unlike the other so-called food bioactives, some carotenoids can be converted into retinoids exhibiting vitamin A activity, which is essential for humans. Furthermore, they are much more versatile as they are relevant in foods not only as sources of vitamin A, but also as natural pigments, antioxidants, and health-promoting compounds. Lately, they are also attracting interest in the context of nutricosmetics, as they have been shown to provide cosmetic benefits when ingested in appropriate amounts. In this work, resulting from the collaborative work of participants of the COST Action European network to advance carotenoid research and applications in agro-food and health (EUROCAROTEN, www.eurocaroten.eu, https://www.cost.eu/actions/CA15136/#tabs|Name:overview) research on carotenoids in foods and feeds is thoroughly reviewed covering aspects such as analysis, carotenoid food sources, carotenoid databases, effect of processing and storage conditions, new trends in carotenoid extraction, daily intakes, use as human, and feed additives are addressed. Furthermore, classical and recent patents regarding the obtaining and formulation of carotenoids for several purposes are pinpointed and briefly discussed. Lastly, emerging research lines as well as research needs are highlighted.

Biotechnological approaches for the production of designer cheese with improved functionality

Cheese is a product of ancient biotechnological practices, which has been revolutionized as a functional food product in many parts of the world. Bioactive compounds, such as peptides, polysaccharides, and fatty acids, have been identified in traditional cheese products, which demonstrate functional properties such as antihypertensive, antioxidant, immunomodulation, antidiabetic, and anticancer activities. Besides, cheese-making probiotic lactic acid bacteria (LAB) exert a positive impact on gut health, aiding in digestion, and improved nutrient absorption. Advancement in biotechnological research revealed the potential of metabolite production with prebiotics and bioactive functions in several strains of LAB, yeast, and filamentous fungi. The application of specific biocatalyst producing microbial strains enhances nutraceutical value, resulting in designer cheese products with multifarious health beneficial effects. This review summarizes the biotechnological approaches applied in designing cheese products with improved functional properties.

Corynebacterium glutamicum CrtR and Its Orthologs in Actinobacteria: Conserved Function and Application as Genetically Encoded Biosensor for Detection of Geranylgeranyl Pyrophosphate

Carotenoid biosynthesis in Corynebacteriumglutamicum is controlled by the MarR-type regulator CrtR, which represses transcription of the promoter of the crt operon (PcrtE) and of its own gene (PcrtR). Geranylgeranyl pyrophosphate (GGPP), and to a lesser extent other isoprenoid pyrophosphates, interfere with the binding of CrtR to its target DNA in vitro, suggesting they act as inducers of carotenoid biosynthesis. CrtR homologs are encoded in the genomes of many other actinobacteria. In order to determine if and to what extent the function of CrtR, as a metabolite-dependent transcriptional repressor of carotenoid biosynthesis genes responding to GGPP, is conserved among actinobacteria, five CrtR orthologs were characterized in more detail. EMSA assays showed that the CrtR orthologs from Corynebacteriumcallunae, Acidipropionibacteriumjensenii, Paenarthrobacternicotinovorans, Micrococcusluteus and Pseudarthrobacterchlorophenolicus bound to the intergenic region between their own gene and the divergently oriented gene, and that GGPP inhibited these interactions. In turn, the CrtR protein from C. glutamicum bound to DNA regions upstream of the orthologous crtR genes that contained a 15 bp DNA sequence motif conserved between the tested bacteria. Moreover, the CrtR orthologs functioned in C. glutamicum in vivo at least partially, as they complemented the defects in the pigmentation and expression of a PcrtE_gfpuv transcriptional fusion that were observed in a crtR deletion mutant to varying degrees. Subsequently, the utility of the PcrtE_gfpuv transcriptional fusion and chromosomally encoded CrtR from C. glutamicum as genetically encoded biosensor for GGPP was studied. Combined FACS and LC-MS analysis demonstrated a correlation between the sensor fluorescent signal and the intracellular GGPP concentration, and allowed us to monitor intracellular GGPP concentrations during growth and differentiate between strains engineered to accumulate GGPP at different concentrations.

Strain-Level Diversity Impacts Cheese Rind Microbiome Assembly and Function

Diversification can generate genomic and phenotypic strain-level diversity within microbial species. This microdiversity is widely recognized in populations, but the community-level consequences of microbial strain-level diversity are poorly characterized. Using the cheese rind model system, we tested whether strain diversity across microbiomes from distinct geographic regions impacts assembly dynamics and functional outputs. We first isolated the same three bacterial species (Staphylococcus equorum, Brevibacterium auranticum, and Brachybacterium alimentarium) from nine cheeses produced in different regions of the United States and Europe to construct nine synthetic microbial communities consisting of distinct strains of the same three bacterial species. Comparative genomics identified distinct phylogenetic clusters and significant variation in genome content across the nine synthetic communities. When we assembled each synthetic community with initially identical compositions, community structure diverged over time, resulting in communities with different dominant taxa. The taxonomically identical communities showed differing responses to abiotic (high salt) and biotic (the fungus Penicillium) perturbations, with some communities showing no response and others substantially shifting in composition. Functional differences were also observed across the nine communities, with significant variation in pigment production (light yellow to orange) and in composition of volatile organic compound profiles emitted from the rinds (nutty to sulfury).IMPORTANCE Our work demonstrated that the specific microbial strains used to construct a microbiome could impact the species composition, perturbation responses, and functional outputs of that system. These findings suggest that 16S rRNA gene taxonomic profiles alone may have limited potential to predict the dynamics of microbial communities because they usually do not capture strain-level diversity. Observations from our synthetic communities also suggest that strain-level diversity has the potential to drive variability in the aesthetics and quality of surface-ripened cheeses.

Antiproliferative activity of carotenoid pigments produced by extremophile bacteria

Various microorganisms are able to synthesize pigments, which usually present antioxidant properties. The aim of this work was to evaluate the antiproliferative activity of bacterial pigments against cancer cells Neuro-2a, Saos-2 and MCF-7. Pigments were obtained from Deinococcus sp. UDEC-P1 and Arthrobacter sp. UDEC-A13. Both bacterial strains were isolated from cold environments (Patagonia and Antarctica, respectively). Pigments were purified and analyzed by HPLC. Antiproliferative activity was evaluated by 3-4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium (MTT) assay. Deinoxanthin carotenoid obtained from Deinococcus sp. UDEC-P1 was able to reduce significatively the viability of Saos-2 (37.1%), while no effect was observed against MCF-7 and Neuro-2a. Pigments obtained from Arthrobacter sp. UDEC-A13 showed a significant viability reduction of three tumour cells (20.6% Neuro-2a, 26.3% Saos-2 and 13.2% MCF-7). Therefore, carotenoid pigments produced by extremophilic bacteria Deinococcus sp. UDEC-P1 and Arthrobacter sp. UDEC-A13 could be proposed as novel complementary compounds in anticancer chemotherapy.

Light-inducible carotenoid production controlled by a MarR-type regulator in Corynebacterium glutamicum

Carotenoid production in some non-phototropic bacteria occurs in a light-dependent manner to protect cells from photo-oxidants. Knowledge regarding the transcriptional regulator involved in the light-dependent production of carotenoids of non-phototrophic bacteria has been mainly confined to coenzyme B₁₂-based photo-sensitive regulator CarH/LitR family proteins belonging to a MerR family transcriptional regulator. In this study, we found that bacteria belonging to Micrococcales and Corynebacteriales exhibit light-dependent carotenoid-like pigment production including an amino acid-producer Corynebacterium glutamicum AJ1511. CrtR is a putative MarR family transcriptional regulator located in the divergent region of a carotenoid biosynthesis gene cluster in the genome of those bacteria. A null mutant for crtR of C. glutamicum AJ1511 exhibited constitutive production of carotenoids independent of light. A complemented strain of the crtR mutant produced carotenoids in a light-dependent manner. Transcriptional analysis revealed that the expression of carotenoid biosynthesis genes is regulated in a light-dependent manner in the wild type, while the transcription was upregulated in the crtR mutant irrespective of light. In vitro experiments demonstrated that a recombinant CrtR protein binds to the specific sequences within the intergenic region of crtR and crtE, which corresponds to −58 to −7 for crtE, and +26 to −28 for crtR with respect to the transcriptional start site, and serves as a repressor for crtE transcription directed by RNA polymerase containing SigA. Taken together, the results indicate that CrtR light-dependently controls the expression of the carotenoid gene cluster in C. glutamicum and probably closely related Actinobacteria.

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.

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.

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