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The Ecological Impact of Introducing a Foreign Organism into the
Turfgrass Ecosystem
Von Sigler
Objective
The objective of this study was to determine the ecological effect of introducing a
high concentration of a biological control organism into the turfgrass environment.
Rationale
The use of biological control organisms to augment chemical pesticide applications is
gaining popularity amongst the environmentally conscious. While a moderate amount of
information is known about the effect of pesticides on the indigenous ecology of a given
environment, relatively little data exists describing the effect of introducing living
organisms to a native community, especially a turfgrass system. Pesticides, organic
matter, and nutrients are all cycled by the activity of microorganisms in the natural
environment. In order to assess the potential risks to these processes one must understand
the effects of inputs such as the application of living organisms on native members of the
turfgrass community.
How it was done
Approximately 106 cfu ml-1 of P. aureofaciens was applied
nightly to an established creeping bentgrass through the existing irrigation system. The
bacteria were applied in 0.1 inch of water. To determine the effect of repeated, high
concentration P. aureofaciens applications on the indigenous turfgrass environment
bacteria, samplings of the leaves, thatch, and soil (~1 inch depth) were made
periodically. DNA was extracted from each matrix and subsequently PCR amplified using
primers specific for bacterial 16SrDNA sequences. Samples were electrophoresed across a
denaturing gradient to separate bands of differing sequence and to produce a molecular
"fingerprint" of the bacterial population. Banding patterns of leaf thatch and
soil samples with and without P. aureofaciens treatments were compared. Bands that
either appeared or regressed (representing effected bacteria) according to the P.
aureofaciens applications were excised from the gel, cloned into E. coli, and
sequenced to determine bacterial identity.
Results to date
The effect of P. aureofaciens applications on the indigenous bacterial community
was most pronounced in the turfgrass canopy(Fig. 1). Although only one bacterial member of
the population was impacted following the P. aureofaciens treatments (as detected
by one regressing band), this bacteria was effected greatly as indicated by the
diminishing intensity of its band..
Little detectable variation exists between control and treated samples with regard to
the thatch layer (Fig. 1), and no detectable changes in population structure were evident
in the soil (data not shown).
Excision and sequencing of the regressing band followed by alignment within existing
databases suggests that the effected member of the community is from the family Cytophagaceae.
Selected Cytophaga spp. have been reported to be active in producing cellulase
(cellulose degradation), amylase (starch degradation), and chitinase (chitin degradation).
Thus, the effected bacteria may have specific qualities that are desirable in the
turfgrass environment for organic matter breakdown and fungal inhibition.
Regardless of the resulting physiological or biochemical effects imparted on the
turfgrass system by introductions of foreign organisms, further research must assess the
true impact of the selective pressure against members of the bacterial community.
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Figure 1. DGGE of bacterial DNA/PCR samples from (1.) leaf canopy without
P. aureofaciens (PA) application, (2.) leaf canopy with PA application, (3.) thatch
layer with out PA application, (4.) thatch layer with PA application, and (5.) pure PA PCR
product. The arrows denote changes in the leaf surface bacterial populations. Top arrow: Cytophagaceae
DNA which disappears following P. aureofaciens application. Bottom arrow: P.
aureofaciens which is present only after application to the turfgrass system (lane 2,
faint) |
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