fungal spore dispersal -...

Alan J. Neumann, Ph.D.

Indoor Ecology Associates Inc.

FACTORS OF FUNGAL SPORE

DISPERSAL

AND INDOOR BIOAEROSOLS

INDOOR ENVIRONMENTAL QUALITY

ASSESSMENTS

February, 2011 IAQA CONFERENCE 2

• Investigations of indoor environments often include

collection and evaluation of indoor bioaerosols

• Bioaerosols are defined as living organisms, or remains of

organisms, that become airborne

• Collection of representative FUNGAL bioaerosol samples

are one component of the evaluation process

RELATION OF FUNGAL SPORE DISPERSAL

TO INDOOR ENVIRONMENTAL

ASSESSMENT


• Fungi are part of the natural environment

• Fungal species exist in environmental niches to which they have adapted

• They exhibit survival strategies

• They produce natural fungal bioaerosols

• Indoor fungal reservoirs

• Some fungal species have adapted to man-made/indoor environmental niches

• These fungi produce fungal bioaerosols indoors

TERMINOLOGY


• Mould (Illman 1970 Mycologia)

• Derived from a Scandinavian language and refers to something

fuzzy

• Advocated for American use for a fungus rather than ‘mold’

• Microfungus with well-defined mycelium or spore mass

• Hypha

• Filament of fungal cells, attached end-to-end, one cell in width

TERMINOLOGY


• Mycelium

• Mass of hyphae derived from single spore germination; entire colony

• Spore

• General term for a fungal reproductive structure.

• Differentiated form which may be:

• Specialized for dissemination

• Produced in response to adverse environmental conditions

• Produced by sexual or asexual reproductive processes

CELL WALL STRUCTURE


TERMINOLOGY


• Conidium (conidia)

• Specialized, non-motile, asexual spore, not developed by cytoplasmic cleavage (sporangiophore) or free-cell formation (ascus)

• Commonly refers to asexual spores

• 7 types of spores based on shape, septation, and pigmentation (e.g., amerospore, dictyospore, helicospore)

• Conidiophore

• Simple or branched hypha bearing conidiogenous cells


Scanning electron micrograph of a fungal

asexual reproductive body of a species of the

genus Aspergillus

.Image from the College of Veterinary Medicine, Mississippi

State University.

MYXOSTELIDA

• Slime moulds

• Stemonitis spp.

• Upper right – macro of

sporangia

• Lower right – micro of

reticulated interior wall of

sporangium and spores


BASIDIOMYCETES

• Mushrooms are common

basidiomycetes of lawns and

woods

• Spores borne on gill or pore

walls of cap


BASIDIOMYCETES


SEM micrograph of bolete spores

BASIDIOMYCETES


Copied from Dr. Wong U of Hawaii

DEUTEROMYCOTINA


Penicillium atramentosom

By David Spero

DEUTEROMYCOTINA


Memnoniella spp. - UNLV

DEUTEROMYCOTINA


Memnoniella echinata

Copied from Campbell, 1975

DEUTEROMYCOTINA


Memnoniella echinata and Stachybotrys chartarum

Copied from Haugland et al, 2001

DEUTEROMYCOTINA


Stachybotrys spp. – SUNY ESF

CONSIDERATIONS OF SPORE

DISPERSAL CRITERIA


• Dispersal mechanisms evolved with ‘life strategy’ for

survival

• Mechanism for detachment from parent

• Size of spore/conidium

• Most less than 10 mm in diameter

• Environmental factors

• Relative humidity

• Air currents

TERMINOLOGY


• Spore types

• Memnospores

• Spores that remain in place of origin to tide over

unfavorable environmental conditions

• Xenospores

• Spores dispersed to new geographic locations

• Often thin-walled

• Easily detached from parent hypha

SPORE/CONIDIA CHARACTERISTICS


• Stachybotrys chartarum – ellipsoidal, 5-7 X 8-12mm,

gelatinous coat creating clump of spores

• Aspergillus fumigatus – globose, 2.5-3mm

• Cladosporium herbarum – ovate, 2+ cells, 3-23mm

• Epicoccum nigrum – globose to pyriform, multi-celled,

15-25mm

• Penicillium chrysogenum – globose to ellipsoidal,

2.5-4 X 2-3.5mm

AIRBORNE CONSIDERATIONS


• Air layer closest to substrate is referred to as laminar

layer

• Negligible air movement

• Can be a few millimeters in depth to centimeters in

depth

SPORE/CONIDIAL RELEASE


• Most ascomycetes and basidiomycetes on wood substrates do not release spores in low humidity

• Most ascomycetes and basidiomycetes eject spores

• Many moulds such as Cladosporium and Penicillium have no active release mechanism, but are easily detached

• Asp/Pen group will release spores in 0.5 m/sec air flow

• Cladosporium spp. release spores in 1.5 m/sec air flow

RELEASE INTO AIR


• Release must be in moving air above laminar layer

• Active ejection of spores or release from above

ground/substrate level

• Project sporangiophore or conidiophore above laminar air

layer

• Air movement as low as 0.4 m/sec can cause

spores/conidia to become airborne

DISPERSAL PATTERN


Copied from Dr. Wong,

U of Hawaii

MUSHROOM SPORES

• Studies of spores released from mushroom caps indicates

that many drop almost straight down at 0.8 to 3.6 mm/sec

while some may travel 40 meters downwind on air currents

of 1.5 m/sec (Deering et al., 2001)


COLLECTION OF FUNGAL

BIOAEROSOLS


• Spore trap and other impactor collection devices have inherent limitations

• IEQ evaluations routinely set collection device at ‘breathing height’ above the floor

• Concept of bioaerosol dispersal

• Location of bioaerosol source

• Ambient relative humidity

• Air turbulence patterns within the collection area

FALL RATE OF SPORES/CONIDIA


• Ingold suggests that most airborne spores are 10mm or

less in aerodynamic diameter with a fall rate of less than 1

cm/sec

• (about 4 hours for 6 foot fall)

• Fall rate for spherical spores in still air is governed by

Stokes’ Law

• V = 2/9 x q-P/m x gr2

STOKES’ LAW

V = 2/9 x d – P /m x gr2

• V = steady velocity in cm/sec

• d = density of spore (1.0)

• P = density of air (1.0)

• g = acceleration due to gravity

• m = viscosity of air

• r = radius of spore


Scopularia spp. –by Dave Spero

STOKES’ LAW

• Measurements of 4mm spores of Lycoperdon = 0.05

cm/sec

• Spores of Stachybotrys are calculated to settle at a rate

or 1.9 mm/sec, in still air (or 1 meter in 9 minutes)

• Spores of Aspergillus are calculated to settle at a rate of

0.3 mm/sec, in still air


COMMON NATURAL FUNGAL

BIOAEROSOLS


• Common conidia of mould taxa recovered outdoors:

• Cladosporium herbarum, Alternaria spp., Botrytis spp.,

Epicoccum spp.

• Basidiospores common in summer and autumn

• Phylloplane fungi commonly identified in analyses of total

countable fungal bioaerosol samples

• Stachybotrys spores require strong air turbulence (1.6

m/sec air flow) to release 0.1% of conidia; 99% reduction

in spore release after 5 minutes

COMMON MOULDS


• Species of Cladosporium, Penicillium, Aspergillus, and

Botrytis exhibit long conidiophore stalks that raise

conidial masses above laminar layer of air

• Spore release appears to correlate with slight vibrations or

air turbulence

• Spore release appears greatest in low relative humidity (micro niche measurements?)

STUDY DATA


• In general, spores of Cladosporium herbarum, Penicillium spp., and Chaetomium spp. are 2 – 60 mm in diameter

• May require ‘mist’ (e.g., morning dew or rain) to aid release

• Periodicity of spore release suggests circadian rhythm related to temperature and relative humidity

• Often mid-summer peak

• Usual mid-day peak

STUDY DATA


• Study in Oklahoma (Burch and Levitan, 1998) determined a correlation between spore release, in outdoor settings, by common moulds ambient climatic conditions such as temperature and relative humidity

• Bioaerosol concentrations of ascospores and basidiospores appear to peak in before dawn, with increase in humidity

• Bioaerosol concentrations of phylloplane moulds (e.g., species of Cladosporium) peak mid-morning in warm, dry weather

STUDY DATA


• Kansas study indicated release of Cladosporium spores peaked mid-morning in relation to increased ambient temperature, decrease in relative humidity, and ripening of conidia (i.e., maturation)

• Fungal colonies may produce spores in 106 to 109 quantities

• Dr. Kendricks estimated 4 X 106 spores released from a 1 inch diameter colony of Penicillium spp. at first air movement

• Fungal spores may be carried 1 meter to >500 km from source

INDOOR CONSIDERATIONS


• Saprophytic fungi can and do grow in indoor

environments, even without significant water damage or

moisture content

• Horner, et al. 2004; Cooley et al. 1998

• Indoor environment commonly climate controlled by

HVAC systems

• Ambient indoor temperature and RH change hourly

and daily

• Air turbulence by indoor activity and HVAC air

handler operation

INDOOR BIOAEROSOLS


• Anecdotal collection data from Dr. George Wong (U of Hawaii)

• Serial collection of fungal bioaerosols using culture plates in same location indicated fewer spores trapped after first collection (85 CFU in first plate to 20 CFU on fourth plate)

• Air eddies and turbulence in buildings with central HVAC keeps fungal conidia airborne

• Estimated fungal bioaerosol concentrations change over time and by location of sampling device

EVALUATION OF IEQ BIOAEROSOL

DATA


• Considerations:

• Limitations of collection technique

• Location of sample collection

• Number of sample locations and samples per location

• Correlation to IAQ parameters (temp and RH)

• Nature of various release mechanisms

• Time of sampling

• Number of and time of outdoor samples

EVALUATION OF IEQ BIOAEROSOL

DATA


• Considerations

• Operation of AFD in a contained remediation site

• Movement within a still air site

• Rate of fall for common conidia and spores

• Types of spores/conidia that may be airborne

• Stachybotrys spores do not readily become airborne

• Stachy spores may become airborne after desiccation

GENERAL REFERENCES


• Burnett, J. H. and A.P.J. Trinici. Eds. 1979. Fungal Walls and Hyphal Growth. Cambridge Univ. Press.

• Gravesen, S. et al. 2001. Microfungi. Munksgaard.

• Ingold, C. T. 1971. Fungal Spores. Their liberation and dispersal. Clarendon Press.

• Ingold, C. T. 1973. The Biology of the Fungi. 2nd Ed. Hutchinson educational Ltd.

• Kendrick, B. 2002. The Fifth Kingdom. 3rd Ed. R. Pullins Co.

• Kirk, P. M. et. al. Eds. 2001. Dictionary of the Fungi. 9 th Ed. CABI Bioscience.

• Medlin, M. F. Ed. 1966. The Fungus Spore. Butterworth.

• Watanabe, T. 1994. Pictorial Atlas of Soil and Seed Fungi. Lewis Publishers

QUESTIONS ??


• Please wake the person next to you before you leave.

• Contact for copy of presentation:

• IAQA website or

• [email protected]

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