Image analysis for quantification of bacterial rock weathering

Developed by Maria Esther Puente

Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), La Paz, B.C.S., Mexico

In collaboration with:

Yoav Bashan, The Bashan Foundation, Corvallis, OR, USA

Carmen Rodriguez-Jaramillo, Image Analysis Analytical Service, Northwestern Center for Biological Research (CIBNOR), La Paz, B.C.S., Mexico

Ching-Yan Li- Pacific Northwest Research Station, Forestry Sciences Laboratory, USDA Forest Service, Corvallis, OR, USA

Rock particle undergoing image analysis
Click on photo to enlarge

A fast, quantitative technique of image analysis was developed to measure the potential of rock and stone weathering by microorganisms.

The technique is based on reduction of the surface area of rock particles by microbes and counting the relative increase in the number of small particles in ground rock slurries. This was done by recording changes in ground rock samples with an electronic image analyzing process. The slurries were previously amended with carbon source, ground to a uniform particle size, and incubated with rock-weathering bacteria for 28 days or as needed. The technique was developed and tested, using two rock-weathering bacteria Pseudomonas putida and Azospirillum brasilense on marble, granite, apatite, quartz, limestone, and volcanic rock substrates.

The image analyzer rapidly processed large number of particles (10100x 106 per sample) so the capacity of bacteria to weather rock particles can be accurately measured, statistics is easy to perform, and many samples can be processed in a short time.

This technique was developed to substitute conventional subjective estimates of rock weathering by microorganisms, save work time, and reduce eye and headaches pains from counting procedures under a microscope.

This method can give an accurate evaluation of the potential damage of local microorganisms residing on stone can inflict on the stone when proper conditions for bacterial growth occur, such as irrigation of agricultural land or bird droppings and dust particulates combined with rain on monuments and buildings. However, this method does not evaluate the actual rate of weathering of stone under conditions that are not conducive to microbial growth, a condition that prevails for long periods in dry areas.

This website contains technical specifications of the procedure and tips, a list of necessary chemicals, photographs (in the photo gallery), and a PDF file of the publication that originally described the procedure and a research paper demonstrating the feasibility of the technique.