1. Mariya Smit and Holly Simon
Biosensor technologies for monitoring and prediction of microbial community response to environmental change.
Mariya Smit and Holly Simon

2. Goals
Identify metabolic processes that differentiate microbial communities across aquatic habitats;
Characterize microbial metabolic responses to chemical and physical gradients.
Challenges:
Limited knowledge about composition of microbial communities;
High complexity and temporal changes of microbial metabolism;
Paucity of genomic sequence information for environmental microbes.

3. Methods: DNA microarrays
Biosensor-based technologies for nucleic acid analysis.
Water sample RNA Labeled targets Hybridization Microarray Data
Microarray Probes
Biosensors*
DNA Microarrays= High throughput biosensors based
on nucleic acid hybridization
*Biological recognition of a target analyte by a specific probe with subsequent physicochemical detection of the target:probe interaction.
Well-established for simultaneous analysis of thousands of genes;
High cost (hundreds of dollars per experiment);
Fluorescent detection requiring lab conditions and large equipment.

4. Other types of biosensors
Requirements that are not fulfilled with DNA microarrays:
Deployment in field conditions:
Portability and tolerance of mechanical disturbances;
Low costs of operation to enable analysis of thousands of samples;
Label-free and real-time procedure to decrease the assay time.
Formats:
A novel impedance-based biosensor from Sharp Labs of America (SLA).
Our approach:
First, DNA microarrays to select the analytes of interest from thousands present in the samples.
Second, low-cost biosensors to assay the selected analytes in time series across chemical and physical gradients in different habitats.
Like planes and helicopters: both are used to fly, but have very different applications.

5. Oligonucleotide DNA microarray format
Commercial from CombiMatrix
Oligonucleotide probes between 25 and 40 nucleotides in length.
Custom synthesis: user-defined probe content.
Re-usable up to 4-5 times.
12,000 spots.
Microelectrodes
45 mm
Semiconductor
Microarray Probe Design:
CombiMatrix software to select probes from a user-defined gene list;
Probe specificity check against a user-defined sequence dataset (in our case, rDNA sequences).

6. Oligonucleotide probe design
1. Selection of 5000 group-specific, or “common” probes from 11 species present in Columbia River a b g
Actinobacteria
Bacteroidetes
Proteobacteria
Proportion of probes specific for taxonomic groups
2. Selection of 7000 “function signature” probes specific for particular genes involved in nitrogen and carbon metabolism. 251 species of environmental bacteria.
Nitrogen
metabolism
Carbon 48 27 25
Fe-S enzymes
Proportion of probes specific for functional categories of genes of interest
Total: 12,000 probes

7. Microarray Hybridization
Hybridization Image
12K format with 12,000 different probes;
Hybridization with:
Pool of salinity gradient samples
(6-28 PSU);
Fresh water sample pool (0 PSU);
Salt water sample pool (32-33 PSU).
Goals:
Selection of probes that show significant
(above background) signals;
Selection of probes that are differentially
expressed among the sample pools.

8. Differential gene expression between fresh and salt water habitats
Scatter plot: for each probe, X-axis is Log2(Intensity) in Fresh, and Y-axis is Log2(Intensity) in Salt water pools.
2-fold cut-off
Up-regulated in Salt water
Salt water: Log2(Intensity)
Up-regulated in Fresh water
Fresh water: Log2(Intensity)
The majority of probes are expressed at similar levels in both habitats;
Approximately 1300 probes are differentially expressed (>2-fold) between fresh and salt water.

9. Clustering of gene expression patterns
2D clustering of 641 probes that are differentially expressed in at least one comparison of sample pools.
Well-defined gene expression patterns correlating with different habitats.
Log2(Ratio) –
Fold change
Upregulated in Fresh and/or Mix FS
Upregulated in Salt
Probes
Comparisons
Fresh/Salt
FS/Salt
FS/Fresh
Upregulated in Mix FS vs both Fresh and Salt pools
UP in Salt vs Mix FS and Fresh pools.
DOWN in Mix FS vs Salt and Fresh pools.
UP in Fresh and Mix FS vs Salt pool.

10. Towards development of a deployable biosensor
A novel impedance-based biosensor from Sharp Labs of America (SLA)
Principle: Formation of target-probe hybrids on the electrode surface causes changes in parameters of alternating current
electrode
solution
dielectric layer
probes
Proof of concept: detection of a species of Archaea in a mixed culture using probes against 16S rDNA.
Impedance Z
Advantages:
Label-free, real-time and rapid detection;
Inexpensive devices;
Local company (Camas, WA).
Sample
Injection
30 pM
3 nM

11. Acknowledgements CMOP: Sharp Labs of America: Holly Simon
Lydie Herfort
Jon Schnorr
Mikaela Selby
Pete Kahn
Dan Murphy
Peter Zuber
Bill Howe
Antonio Baptista
Sharp Labs of America:
Andrei Gindilis
John Hatrzell
David Evans
Paul Schuele
CombiMatrix Corporation:
Dominic Suciu