Occupants and surface types drive microbial dynamics in controlled indoor environments

Hou, Jianjian (author), Nakajima, Makiko (author), Nishiuchi, Yukiko (author), Ogura, Daisuke (author), Teramoto, Atsushi (author), Kuratomi, China (author), Iwamoto, Yoko (author), Okamura, Yoshiko (author), Moriguchi, Kazuki (author), Dovjak, Mateja (author), Takayama, Kento (author), Tsugami, Yusaku (author), Fujiyoshi, So (author), Maruyama, Fumito (author)

Background Indoor microbial communities play a critical role in infuencing indoor environmental quality and human health and are shaped by occupant activity, surface characteristics, and environmental conditions. While previous studies have examined these factors individually, systematic evaluations of their combined interactions, particularly involving Heating, Ventilation, and Air Conditioning (HVAC) and drainage systems, remain limited. This controlled, long-term (1.5-year) investigation assessed how human occupancy, surface moisture (dry vs. wet), aquaponics (soilless plant-aquarium systems), and environmental parameters (humidity, ventilation, and seasonal variations) infuence bacterial and eukaryotic dynamics in tightly sealed residential units. Results Continuous air-conditioner operation without fresh-air intake led to elevated CO₂ levels during occupancy and pronounced seasonal humidity fuctuations, emphasizing the need for improved ventilation and adaptive humidity control in compact urban residences. Amplicon sequencing revealed higher microbial diversity on dry surfaces (aerosols, air-conditioner flter dust, and foor dust) than on wet surfaces (waste drains and showerheads). Wet environments supported bioflm-associated taxa adapted to moist conditions (e.g., Methylobacterium, Vermamoeba). Human occupancy signifcantly enriched air-conditioner flter dust with opportunistic bacteria (e.g., Finegoldia and Streptococcus), underscoring occupant-driven microbial accumulation via recirculated air. Additionally, the smallscale aquaponic system had minimal measurable infuence on microbial composition at the room scale, suggesting limited aerosolization or dispersal under typical usage conditions. Indoor relative humidity was signifcantly correlated with microbial diversity in air systems, notably enhancing moisture-adapted taxa such as Sphingomonas during humid seasons. Seasonal variations markedly infuenced eukaryotic communities (e.g., pollen infux).

• Language: English
• Keywords: built environment, indoor microbiome, eukaryote, occupancy, aquaponics, season, surface moisture, humidity, human health
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: 23 str.
• Numbering: Vol. 20, art. 114
• PID: 20.500.12556/RUL-172849
• UDC: 699.8
• ISSN on article: 2524-6372
• DOI: 10.1186/s40793-025-00775-6
• COBISS.SI-ID: 248296707
• Publication date in RUL: 11.09.2025

Record is a part of a journal

• Title: Environmental microbiome
• Shortened title: Environ. microbiome
• Publisher: BMC
• ISSN: 2524-6372
• COBISS.SI-ID: 529784601

Licences

• License: CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
• Link: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Description: The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.

Secondary language

• Language: Slovenian

Abstract

Ozadje Mikrobne skupnosti v notranjih prostorih pomembno vplivajo na kakovost notranjega okolja in zdravje ljudi. Oblikujejo jih dejavnosti uporabnikov, značilnosti površin in okoljski pogoji. Čeprav so prejšnje študije preučevale te dejavnike posamezno, je sistematična ocena njihovih medsebojnih vplivov – zlasti v povezavi s sistemi za ogrevanje, prezračevanje in klimatizacijo (HVAC) ter odvodnjavanjem – še vedno omejena. Ta nadzorovana, dolgoročna (1,5-letna) raziskava je preučevala, kako človeška prisotnost, vlaga površin (suhe vs. mokre), akvaponika (sistemi brez zemlje z rastlinami in akvariji) ter okoljski parametri (zračna vlaga, prezračevanje in sezonske spremembe) vplivajo na bakterijsko in evkariontsko dinamiko v tesno zaprtih stanovanjskih enotah. Rezultati Neprekinjeno delovanje klimatske naprave brez dovoda svežega zraka je med prisotnostjo ljudi povzročilo povišane ravni CO₂ in izrazita sezonska nihanja zračne vlage, kar poudarja potrebo po boljšem prezračevanju in prilagodljivem uravnavanju vlage v urbanih stanovanjih. Sekvenciranje ampliconov je pokazalo večjo mikrobno raznolikost na suhih površinah (aerosoli, prah iz filtrov klimatskih naprav, talni prah) kot na mokrih površinah (odtoki, tuš glave). Mokra okolja so podpirala biofilmom prilagojene taksone, kot sta Methylobacterium in Vermamoeba. Prisotnost ljudi je bistveno obogatila prah iz filtrov klimatskih naprav z oportunističnimi bakterijami (npr. Finegoldia, Streptococcus), kar kaže na kopičenje mikrobov zaradi kroženja zraka. Majhen akvaponski sistem ni imel merljivega vpliva na mikrobno sestavo v prostoru, kar nakazuje omejeno aerosolizacijo ali širjenje pri običajni uporabi. Relativna zračna vlaga je bila pomembno povezana z mikrobno raznolikostjo v zra čnih sistemih, zlasti z večjo prisotnostjo vlagi prilagojenih taksonov, kot je Sphingomonas, v vlažnih sezonah. Sezonske spremembe so močno vplivale na evkariontske skupnosti (npr. vnos cvetnega prahu).

• Keywords: grajeno okolje, notranji mikrobiom, evkariont, zasedenost, akvaponika, letni čas, vlaga na površini, zračna vlaga, zdravje ljudi

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: BI-JP/23-25-002-2023
• Name: Vloga okoljskih parametrov za strukturo mikrobnih združb v stavbah v Sloveniji in na Japonskem

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0158-2018
• Name: Gradbene konstrukcije in gradbena fizika