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Applied and Environmental Microbiology, February 2000, p. 694-699, Vol. 66, No. 2
Belle W. Baruch Institute for Marine Biology
and Coastal Research1 and Department of
Biological Sciences,3 University of South
Carolina, Columbia, South Carolina 29208, and Chemistry
Department, FCT/UNL, and ITQB/UNL, 2780-901 Oeiras,
Portugal2
Received 27 August 1999/Accepted 28 October 1999
The microbial community compositions of surface and subsurface
marine sediments and sediments lining burrows of marine polychaetes and
hemichordates from the North Inlet estuary (near Georgetown, S.C.) were
analyzed by comparing ester-linked phospholipid fatty acid (PLFA)
profiles with a back-propagating neural network (NN). The NNs were
trained to relate PLFA inputs to sediment type outputs (e.g., surface,
subsurface, and burrow lining) and worm species (e.g., Notomastus
lobatus, Balanoglossus aurantiacus, and
Branchyoasychus americana). Sensitivity analysis was used
to determine which of the 60 PLFAs significantly contributed to
training the NN. The NN architecture was optimized by changing the
number of hidden neurons and calculating the cross-validation error
between predicted and actual outputs of training and test data. The
optimal NN architecture was found to be four hidden neurons with
60-input neurons representing the 60 PLFAs, and four output neurons
coding for both sediment types and worm species. Comparison of
cross-validation results using NNs and linear discriminant analysis
(LDA) revealed that NNs had significantly fewer incorrect
classifications (2.7%) than LDA (8.4%). For the NN cross-validation,
both sediment type and worm species had 3 incorrect classifications out
of 112. For the LDA cross-validation, sediment type and worm species
had 7 and 12 incorrect classifications out of 112, respectively.
Sensitivity analysis of the trained NNs revealed that 17 fatty acids
explained 50% of variability in the data set. These PLFAs were highly
different among sediments and burrow types, indicating significant
differences in the microbiota.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Application of Neural Computing Methods for
Interpreting Phospholipid Fatty Acid Profiles of Natural
Microbial Communities
*
Corresponding author. Mailing address: Belle W. Baruch
Institute for Marine Biology and Coastal Research, University of South Carolina, Columbia, SC 29208. Phone: (803) 777-3928. Fax: (803) 777-3935. E-mail: noble{at}biol.sc.edu.
This is contribution number 1192 of the Belle W. Baruch Institute
for Marine Biology and Coastal Research.
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