{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T08:28:15Z","timestamp":1787646495087,"version":"build-2736575974"},"reference-count":28,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T00:00:00Z","timestamp":1787616000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001691","name":"JSPS KAKENHI","doi-asserted-by":"publisher","award":["25K12980"],"award-info":[{"award-number":["25K12980"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Life"],"abstract":"<jats:p>Objective: Simulated microgravity (SMG) alters fluid dynamics and may influence microbial aggregation. However, its effects on oral bacteria remain unclear. This study investigated the effects of SMG on the growth and aggregation of representative oral bacteria. Methods: Four facultative oral bacteria representing distinct ecological and adhesive properties\u2014Staphylococcus aureus(opportunistic pathogen), Streptococcus mutans (glucan-producing cariogenic bacterium), Streptococcus salivarius (commensal fructan-producing bacterium), and Streptococcus sanguinis (early colonizer)\u2014together with the periodontal pathogen Porphyromonas gingivalis were cultured under SMG (10\u22123G) or normal gravity (NG). Streptococci were grown with or without sucrose to evaluate the role of extracellular polysaccharides. Growth was assessed by optical density, and aggregation was quantified by image analysis. Results: SMG induced aggregation in a species-dependent manner. S. mutans and S. salivarius formed spherical aggregates under SMG, whereas little or no aggregate formation was observed in S. aureus, S. sanguinis, or P. gingivalis. Aggregation of S. mutans was markedly reduced without sucrose, indicating dependence on glucan-mediated adhesion. S. salivarius also showed reduced aggregation under sucrose-free conditions, although limited aggregation persisted. Growth kinetics were virtually unaffected by SMG. Conclusions: SMG promotes aggregation of selected oral bacteria through species-specific mechanisms. These findings suggest that microgravity may alter the architecture of oral microbial communities by enhancing particular intercellular adhesion pathways.<\/jats:p>","DOI":"10.3390\/life16091402","type":"journal-article","created":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T08:00:48Z","timestamp":1787644848000},"page":"1402","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Species-Dependent Aggregation of Oral Bacteria Under Simulated Microgravity"],"prefix":"10.3390","volume":"16","author":[{"given":"Ryosuke","family":"Hanai","sequence":"first","affiliation":[{"name":"Department of Orthodontics, School of Dentistry, Aichi Gakuin University, 2-11 Suemori-dori, Chikusa-ku, Nagoya 464-8651, Japan"},{"name":"Department of Microbiology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Makoto","family":"Hirohata","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2598-343X","authenticated-orcid":false,"given":"Yoshihiko","family":"Sugita","sequence":"additional","affiliation":[{"name":"Department of Oral Pathology\/Forensic Odontology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"},{"name":"Aichi Gakuin University Space Research Center, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7373-9282","authenticated-orcid":false,"given":"Hisataka","family":"Kondo","sequence":"additional","affiliation":[{"name":"Aichi Gakuin University Space Research Center, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan"},{"name":"Junior College, Aichi Gakuin University, Nagoya 464-8651, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5913-2436","authenticated-orcid":false,"given":"Yoshikazu","family":"Naiki","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8426-6444","authenticated-orcid":false,"given":"Kiyoshi","family":"Nishikawa","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mayu","family":"Hida","sequence":"additional","affiliation":[{"name":"Department of Orthodontics, School of Dentistry, Aichi Gakuin University, 2-11 Suemori-dori, Chikusa-ku, Nagoya 464-8651, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yoshiaki","family":"Hasegawa","sequence":"additional","affiliation":[{"name":"Department of Microbiology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ken","family":"Miyazawa","sequence":"additional","affiliation":[{"name":"Department of Orthodontics, School of Dentistry, Aichi Gakuin University, 2-11 Suemori-dori, Chikusa-ku, Nagoya 464-8651, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0436-3357","authenticated-orcid":false,"given":"Hatsuhiko","family":"Maeda","sequence":"additional","affiliation":[{"name":"Department of Oral Pathology\/Forensic Odontology, School of Dentistry, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya  464-8650, Japan"},{"name":"Aichi Gakuin University Space Research Center, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"345","DOI":"10.1128\/MMBR.68.2.345-361.2004","article-title":"Microbial responses to microgravity and other low-shear environments","volume":"68","author":"Nickerson","year":"2004","journal-title":"Microbiol. Mol. Biol. Rev."},{"key":"ref_2","first-page":"108","article-title":"Biofilm dynamics in space and their potential for sustainable space exploration\u2014A comprehensive review","volume":"44","author":"Sowmeya","year":"2025","journal-title":"Life Sci. Space Res."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1089\/ast.2012.0876","article-title":"Ground-based facilities for simulation of microgravity: Organism-specific recommendations for their use, and recommended terminology","volume":"13","author":"Herranz","year":"2013","journal-title":"Astrobiology"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1608","DOI":"10.2174\/1389557523666230109160620","article-title":"Impact of Microgravity on Virulence, Antibiotic Resistance and Gene Expression in Beneficial and Pathogenic Microorganisms","volume":"23","author":"Salavatifar","year":"2023","journal-title":"Mini Rev. Med. Chem."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1038\/s41526-016-0006-4","article-title":"Investigation of simulated microgravity effects on Streptococcus mutans physiology and global gene expression","volume":"3","author":"Orsini","year":"2017","journal-title":"npj Microgravity"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Tesei, D., Jewczynko, A., Lynch, A.M., and Urbaniak, C. (2022). Understanding the Complexities and Changes of the Astronaut Microbiome for Successful Long-Duration Space Missions. Life, 12.","DOI":"10.3390\/life12040495"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"100018","DOI":"10.1016\/j.spaceh.2025.100018","article-title":"Oral health in space: Understanding impacts of microgravity and developing countermeasures for space applications","volume":"1","author":"Chen","year":"2025","journal-title":"Space Habitat."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"471","DOI":"10.1038\/nrmicro2381","article-title":"Oral multispecies biofilm development and the key role of cell-cell distance","volume":"8","author":"Kolenbrander","year":"2010","journal-title":"Nat. Rev. Microbiol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"69","DOI":"10.1159\/000324598","article-title":"Biology of Streptococcus mutans-derived glucosyltransferases: Role in extracellular matrix formation of cariogenic biofilms","volume":"45","author":"Bowen","year":"2011","journal-title":"Caries Res."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"3050","DOI":"10.1128\/AEM.72.4.3050-3053.2006","article-title":"Safety assessment of the oral cavity probiotic Streptococcus salivarius K12","volume":"72","author":"Burton","year":"2006","journal-title":"Appl. Environ. Microbiol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1016\/j.ajic.2014.09.015","article-title":"Staphylococcus aureus and the oral cavity: An overlooked source of carriage and infection?","volume":"43","author":"McCormack","year":"2015","journal-title":"Am. J. Infect. Control"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"30","DOI":"10.1038\/nri3785","article-title":"Periodontitis: From microbial immune subversion to systemic inflammation","volume":"15","author":"Hajishengallis","year":"2015","journal-title":"Nat. Rev. Immunol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"190","DOI":"10.1016\/j.jdsr.2021.09.003","article-title":"Porphyromonas gingivalis FimA and Mfa1 fimbriae: Current insights on localization, function, biogenesis, and genotype","volume":"57","author":"Hasegawa","year":"2021","journal-title":"Jpn. Dent. Sci. Rev."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"100782","DOI":"10.1016\/j.job.2026.100782","article-title":"Diversity and assembly mechanisms of Porphyromonas gingivalis fimbriae: Conservation and structural heterogeneity of type V fimbriae","volume":"68","author":"Hasegawa","year":"2026","journal-title":"J. Oral. Biosci."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3333","DOI":"10.1099\/mic.0.028928-0","article-title":"Anchoring and length regulation of Porphyromonas gingivalis Mfa1 fimbriae by the downstream gene product Mfa2","volume":"155","author":"Hasegawa","year":"2009","journal-title":"Microbiology"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1627","DOI":"10.1099\/00221287-148-6-1627","article-title":"Role of the Streptococcus gordonii SspB protein in the development of Porphyromonas gingivalis biofilms on streptococcal substrates","volume":"148","author":"Lamont","year":"2002","journal-title":"Microbiology"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1793","DOI":"10.1038\/s41598-018-20067-z","article-title":"Structural and functional characterization of shaft, anchor, and tip proteins of the Mfa1 fimbria from the periodontal pathogen Porphyromonas gingivalis","volume":"8","author":"Hall","year":"2018","journal-title":"Sci. Rep."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"e14480","DOI":"10.7717\/peerj.14480","article-title":"Effects of cleaning sports mouthguards with ethylene-vinyl acetate on oral bacteria","volume":"10","author":"Hayashi","year":"2022","journal-title":"PeerJ."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"671","DOI":"10.1038\/nmeth.2089","article-title":"NIH Image to ImageJ: 25 years of image analysis","volume":"9","author":"Schneider","year":"2012","journal-title":"Nat. Methods"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"140","DOI":"10.3934\/microbiol.2018.1.140","article-title":"Bacterial autoaggregation","volume":"4","author":"Trunk","year":"2018","journal-title":"AIMS Microbiol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"7701","DOI":"10.1128\/AEM.01294-06","article-title":"Escherichia coli biofilms formed under low-shear modeled microgravity in a ground-based system","volume":"72","author":"Lynch","year":"2006","journal-title":"Appl. Environ. Microbiol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"3147","DOI":"10.1128\/IAI.68.6.3147-3152.2000","article-title":"Microgravity as a novel environmental signal affecting Salmonella enterica serovar Typhimurium virulence","volume":"68","author":"Nickerson","year":"2000","journal-title":"Infect. Immun."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"16299","DOI":"10.1073\/pnas.0707155104","article-title":"Space flight alters bacterial gene expression and virulence and reveals a role for global regulator Hfq","volume":"104","author":"Wilson","year":"2007","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1221","DOI":"10.1128\/AEM.01582-10","article-title":"Transcriptional and proteomic responses of Pseudomonas aeruginosa PAO1 to spaceflight conditions involve Hfq regulation and reveal a role for oxygen","volume":"77","author":"Crabbe","year":"2011","journal-title":"Appl. Environ. Microbiol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"408","DOI":"10.1016\/j.actaastro.2009.06.007","article-title":"Low-shear modelled microgravity alters expression of virulence determinants of Staphylococcus aureus","volume":"66","author":"Rosado","year":"2010","journal-title":"Acta Astronaut."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"10","DOI":"10.1128\/microbiolspec.GPP3-0051-2018","article-title":"The Biology of Streptococcus mutans","volume":"7","author":"Lemos","year":"2019","journal-title":"Microbiol. Spectr."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Burton, J.P., Wescombe, P.A., Macklaim, J.M., Chai, M.H., Macdonald, K., Hale, J.D., Tagg, J., Reid, G., Gloor, G.B., and Cadieux, P.A. (2013). Persistence of the oral probiotic Streptococcus salivarius M18 is dose dependent and megaplasmid transfer can augment their bacteriocin production and adhesion characteristics. PLoS ONE, 8.","DOI":"10.1371\/journal.pone.0065991"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"3579","DOI":"10.1111\/1462-2920.13853","article-title":"Three glycosylated serine-rich repeat proteins play a pivotal role in adhesion and colonization of the pioneer commensal bacterium, Streptococcus salivarius","volume":"19","author":"Couvigny","year":"2017","journal-title":"Environ. Microbiol."}],"container-title":["Life"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2075-1729\/16\/9\/1402\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T08:12:43Z","timestamp":1787645563000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2075-1729\/16\/9\/1402"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,25]]},"references-count":28,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["life16091402"],"URL":"https:\/\/doi.org\/10.3390\/life16091402","relation":{},"ISSN":["2075-1729"],"issn-type":[{"value":"2075-1729","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,25]]}}}