Microbial biofilms are structures on the order of millimeters that are composed of individual bacterial organisms, each on the order of micrometers. How do they do it? How do these helpless and disposable micro-organisms collectively create intricate networks that diffuse nutrients to various locations of the colony? The fascinating feature of biofilms is that each individual agent is unintelligent, it cannot think or feel or remotely choose the life it will lead, and yet, these amazing structures are built by mere nutrient concentration gradients within the system. Reacting to the amount of nutrient supply, these bacterial organisms can work together to defend, preserve, and expand their colony. In this study, we analyzed how bacterial colonies reacted to local variations in the environment by adding obstacles in their range of growth. Using fluorescent microscopy, we were able to obtain images that display the various phenotypes of the genus, Bacillus Subtilis, growing on an agar substrate through a channel.
The images shown on the left display biofims growing through channels of 2mm, 5mm, and 10mm in width. On the right side, the figures display the normalized signal for three of the phenotypes present in each colony. The three phenotypes are the matrix (green), motility (red), and sporulation (yellow). The bacteria's inoculation point lies at the zero mark along the x-axis. The colony's range of growth along the control side, where no obstacles are present, is represented by the normalized signal on the negative portion of the x-axis. The two vertical, black lines are representative of the beginning and end of the channel lengths.
There is a generally organized structure to the colony, where the matrix cells lie on the edge of colony, motile cells in the second level, and sporulated cells in the center, making it possible for the bacteria to survive and prosper in unfavorable environments, as well as efficiently distribute nutrients to all sections of the colony. The spatiotemporal regulation of gene expression presents interesting results when a biofilm grows through a structure such as the one shown in the images above. We see an increase in the percentage of matrix cells at the edge of the colony with a decrease in the width of the channel. For more details, take a look at my publication in the 2014 NNIN Research Accomplishments booklet.
This work was done as part of the 2014 National Nanotechnology Infrastructure Network (NNIN) REU program under the close advisement of a post-doc, Gareth Haslam, in the Rubinstein lab (Applied Physics) at Harvard University.