Formation of bacterial biofilms

Dr. Neil Canter, Contributing Editor | TLT Tech Beat December 2012

A new signaling system helps to understand how bacteria in sponges communicate with each other.

KEY CONCEPTS
• Research on a specific strain of bacteria living in marine sponges provides further insight into how biofilms are developed.
• A specific SR bacterium known as Ruegeria sp KLH11 was found when present in sufficient numbers to move to another location in the sponge instead of forming a biofilm.
• Researchers hope to get a better understanding of how to stop bacteria from forming biofilms in such places as MWF systems.

BACTERIA HAVE BEEN FOUND TO CAUSE SERIOUS PROBLEMS by hindering the performance of lubricants. Metalworking fluids have been singled out as the largest application where bacteria have such a negative impact because of the large concentration of water present in most of these fluids.

Bacteria grow by consuming the components present in MWFs. This step leads to a deterioration of fluid performance because key additives such as emulsifiers are literally food for the bacteria. The loss of emulsification can be very damaging, and the byproducts released by bacteria can cause corrosion and also can be potentially harmful to workers exposed to the MWF.

Bacteria live by growing on surfaces in the MWF system, which eventually leads to the formation of biofilms. In a previous TLT article, Yves Brun, Clyde Culbertson Professor of Biology at Indiana University in Bloomington, Ind., provided insight on why bacteria form biofilms (1). He said, “Nutrients for bacteria tend to adsorb to surfaces. This leads bacteria to grow on those surfaces where their nutrients are found. As part of this process, bacteria then develop multicellular structures known as biofilms.”

In a MWF system, bacteria secrete an adhesive to attach to surfaces in environments where moisture is present as the first step in forming a biofilm. Most biofilms contain communities of different species of bacteria plus other microorganisms such as fungi, algae, yeast and protozoa. Extracellular polymeric substances that are based on polysaccharides are secreted by the cells in the biofilm to hold this community of microorganisms together.

The typical approach to reduce bacterial populations in MWFs is through the use of antimicrobial pesticides. But the complex structure of biofilms can act to reduce their effectiveness because they literally cannot penetrate to reach the bacteria.

This has led researchers to try to figure out how bacteria decide to adhere to a specific surface. In another previous TLT article, work from Brun and his fellow researchers on how a specific bacterium known as Caulobacter crescentus adheres to a surface is discussed (2). This bacterium attaches to surfaces through a two-step, reversible, irreversible process. In the reversible process, the bacterium applies a low adherence to the surface but can detach at any time. Once the decision is made to permanently adhere to the surface, a powerful polysaccharide-based adhesive is secreted.

Bacteria are able to develop biofilms, even with other living organisms. An interesting example is the presence of bacteria in sponges that live in marine environments. Russell Hill, director of the Institute of Marine and Environmental Technology at the University of Maryland Center for Environmental Science in Baltimore, Md., says, “Bacteria have been found to co-exist with marine sponges in a symbiotic relationship. Our interest in this community stems from the detection of large, organic compounds in these sponges. Many of these compounds were found to be produced by bacteria and not sponges. In fact, several years ago, one of the compounds was commercialized as an anti-cancer drug.

Hill indicates that bacteria can make up as much as 30% to 40% of the biomass of a sponge. He adds, “Based on our studies, the mix of bacteria in the sponge is different from those in the surrounding water column. Sponges appear to provide a stable environment to trap nutrients for the bacteria. One of the objectives of our work is to find out what bacteria are doing to help sponges.”

As part of this process, further insight has been obtained on the steps that bacteria take to form biofilms.

QUORUM SENSING
Hill and his associates have gained a better understanding of how bacteria present in sponges communicate with each other by identifying a new signaling system that ironically causes bacteria to form a flagellum, which enables them to swim away. He adds, “This surprising aspect of our study has provided further information on how bacteria may go about leaving a biofilm.”

For more than 30 years, bacteria have been found to communicate with each other through the use of specific small molecules. Hill explains, “As individual bacterium start to produce these small molecules, growth of the bacterial populations eventually results in a critical density of the molecules being reached, which reflects a bacterial quorum, hence the process is often called Quorum Sensing (QS). At this point, these molecules will then bind to specific proteins in the bacteria to turn specific genes on or off. In this manner, the behavior of bacteria can suddenly change.” One key example cited by Hill is that bacteria can literally become pathogenic towards their host (such as a human being) in this manner.

Certain bacteria living in marine sponges such as those the researchers isolated off the coast of Florida are known as Silicibacter-Ruegeria (SR). Hill says, “We have been able to determine that SR bacteria produce QS molecules known as N-acylhomoserine lactones (AHLs).”

Through detailed studies, the researchers found that in contrast to other bacteria species, their tested SR bacterium called Ruegeria sp KLH11 does not swim by itself. Once a sufficient concentration of AHLs is produced, a group of SR Ruegeria sp KLH11 will produce flagella and move to a new location in the sponge. Hill says, “We believe the bacteria are emigrating from a specific biofilm to move to another location, but we are still uncertain how this process relates to the way bacteria colonize the host.”

The research conducted in this study should contribute to gaining a better understanding of how the most prevalent bacteria species in MWF systems generate biofilms. This result will hopefully lead to the development of new approaches for stopping biofilm formation and, as a consequence, the growth of bacteria.


Figure 3. Researchers identified a signaling system used by the SR bacterium, Ruegeria sp KLH11 isolated from the sponge Mycale laxissima (seen in this photo) to swim away from a specific location in the sponge rather than form a biofilm. This finding may help gain a better understanding of how to reduce the possibility of bacteria forming biofilms. (Courtesy of the University of Maryland Center for Environmental Science)

Further information on this work can be found in a recent article (3) or by contacting Hill at hill@umces.edu.

REFERENCES
1. Canter, N. (2006), “New Adhesive Fights Bacteria Growth in Metalworking Fluids,” TLT, 62 (10), pp. 16-18.
2. Canter, N. (2012), “Bacterial Adhesion on Surfaces,” TLT, 68 (3), pp. 12-13.
3. Zan., J., Cicirelli, E., Mohamed, N., Sibhatu, H., Kroll, S., Choi, O., Uhison, C., Wysoczinski, C., Murphy, R., Churchill, M., Hill, R. and Fuqua, C. (2012), “A Complex LuxR-LuxI Type Quorum Sensing Network in a Roseobacterial Marine Sponge Symbiont Activates Flagellar Motility and Inhibits Biofilm Formation,” Molecular Microbiology, 85 (5), pp. 916-933.

Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.