Pseudomonas syringae: Bioprecipitation Mechanisms and Implications

This is a curated page. Report corrections to Microbewiki.

Overview

By Brandon Byrd

Pseudomonas syringae have a significant impact on weather systems and ecosystems worldwide. This bacteria has previously been studied in depth as a plant pathogen, and it has recently been studied as a major contributor to bioprecipitation. P.syringae are rod shaped, gram-negative bacteria with polar flagella that is a plant pathogen to a wide variety of plant species at cold temperatures (Morris et al 2008). This bacteria is found in agricultural locations as well as non-agricultural locations such as clouds (Morris et al 2008). The fact that it has the capability to grow in a wide range of environments and ecosystems gives this bacteria the potential to drastically impact biogeographical systems. P.syringae also has an extraordinary ice nucleation activity which allows this bacteria to catalyze freezing water at warm temperatures which sparked interest in its role in the water cycle (Maki et al 1974). This is a major key for P.syringae’s effect on biogeographical systems. It is also important to further analyze their ice nucleation ability to understand the mechanisms in which they influence major weather systems such as the water cycle. Furthermore, how P.syringae can impact humans and biodiversity based on their influence on ecosystems and the environment.

History

Fig 1. Scanning Electron Microscopy of Pseudomonas syringae on an ovary of a tomato plant. P.syringae is rod shaped, gram-negative, and has polar flagella. http://www.apsnet.org/publications/phytopathology/backissues/Documents/1983Articles/Phyto73n01_39.PDF.

.

P.syringae are a part of the pseudomonas genus (Figure 1). This genus is gram-negative aerobic proteobacteria. This genus is categorized as pathogens with a wide variety of niche potential due to much variation in metabolism across the species in this genus (Morris 2013).The history of the pseudomonas genus dates back millions of years ago to when they were found in aquatic habitats before plants and land agriculture (Morris et al. 2013). Pseudomonas is still one of the most common bacteria present in many aquatic environments today such as oceans and wetlands. Also, a study done by Pesciaroli and colleagues have shown a new strain of P.syringae to be present in intertidal aquatic environments (Morris et al. 2013). P.syringae was first discovered by Paul Hoppe in 1961 while studying corn crops for the U.S. Department of Agriculture (Parrott 1993). His study demonstrated a bacteria that caused crop freezing problems at temperatures around negative two to four degrees Celsius. His research led to further research in later years which revealed P.syringae and its ice nucleation characteristics which were causing the crop freezing problems. The crop freezing problem that occurred is that between negative eight to four degrees plant stems and roots would freeze due to the presence of P.syringae. Ice nucleation research of P.syringae has led to a cascade of promising discoveries linking this species to important bioprecipitation mechanisms that continue to influence weather in many ecosystems. There was a discovery of ice nucleation proteins that protrude from the outer membrane of P.syringae which facilitates their ice nucleation ability (Morris et al. 2013). These proteins are believed to have arisen without the use of horizontal gene transfer millions of years ago because of evidence of a three secretion system (Morris et al. 2010). The gene for the outer membrane ice nucleation protein is most likely in the core genome of proteobacteria such as pseudomonas syringae. The most likely common ancestor of this gene came from more general orders including Pseudomonadales and also Enterobacteriales (Morris et al. 2013). The study of these ice nucleation proteins have given rise to the present research regarding P.syringae in its direct significance to the water cycle and indirect significance to other biogeographical systems.

Bioprecipitation and P.syringae’s Role in Bioprecipitation

Fig.2 The bioprecipitation cycle diagram with two key factors that highlight the system. First, micro-organisms such as P.syringae that conduct the ice nucleation process. Second, the water vapor from plants, oceans, and aquatic environments that these micro-organism use in the atmosphere. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12447/epdf.

Bioprecipitation is a term used to describe the concept in which precipitation is caused by bacteria. This is important because organisms such as bacteria that can drive our precipitation patterns, due to cloud formation, of any given area can be vital in predicting weather patterns. Also it deepen our understanding of the water cycle and how the water cycle effects ecosystems based on the makeup of the microbial community. Bioprecipitation has a strong correlation with P.syringae. P.syringae is thought to have two significant roles in cloud formation that effect bioprecipitation (Morris et al. 2013). One role is that due to its warm temperature ice nucleation activity, temperatures range from subzero to eight degrees Celsius. P.syringae is an organism that can cause water vapor droplets to freeze at temperatures and conditions that normal abundant mineral ice nucleator particles are unsuccessful at achieving. The second role that this bacteria causes water vapor to freeze to a large enough size for gravity to act on the droplets in clouds which causes precipitation such as snow or rain. This is important because much of rainfall that comes from mid-high altitudes are as result of this water droplet freezing process (Morris et al. 2013). This process either occurs by nucleation minerals present in clouds or microbial life such as P.synrigae that are also present in clouds. As described by in recent studies, P.syringae bioprecipitiation is constructed within the water cycle (Christner 2012). It was first discovered by a man named David Sands in the 1970s. Sands found the same pseudomonas bacteria that caused frost damage was also found in the rainfall of that area (Prasanth 2015). The bioprecipitation process can be compartmentalized and explained in a few steps within the water cycle (Figure 2). The first step is for ice nucleators such as P.syringae to become airborne in atmosphere ready to act on water vapor and ice nuclei at very low temperatures. The second step is for ice nucleation to occur using proteins that P.syringae possesses to facilitate this process. At this step cloud formation occurs and condensation of water vapor and ice nuclei takes place. The third step is traditional for the water cycle: the cloud becomes too heavy and gravity pulls the snow, rain, or any other form of precipitation from the cloud down to the Earth’s surface. This cycle continues which could potentially have a major impact on cloud formation and climate patterns. However, it has been found that P.syringae only accounts for only a small fraction of the total microbial life deposited by rainfall (Christner 2012). This makes it difficult to make the claim that bioprecipitation caused by P.syringae influences ecosystems on a global scale. However, research has suggested that P.syringae and other similar bacteria lose their ability to be cultured but continue their high ice nucleation activity (Christner 2012). This leaves more opportunity to explore how the rate of ice nucleation via P.syringae effects bioprecipitation despite their low atmospheric population discovered through precipitation samples. Also, the potential potency of P.syringae increases because they are able to grow in a wide range of environments (Morris et al. 2014). This bacteria’s life cycle can be conducted in air-borne environments, as well as soil and non-air-borne environments. Other microbial species’ life cycle are heavily dependent on air-borne distribution and deposition through rainfall. These species have recently been shown to be high in ice nucleation activity as well (Morris et al. 2014). This is noteworthy because more microbes other than P.syringae may have a high impact on bioprecipitation. This could also potentially explain the low population numbers of P.syringae in precipitation samples. A deeper understanding of P.syringae’s protein structure and function regarding ice nucleation is important to expanding knowledge on bioprecipitation as a whole.

Mechanisms for Ice Nucleation

Fig.3 Ice nucleation activity of P.synerigae cells in the inner and outer membrane at varying temperatures. Different shapes indicate different treatments with varying concentrations of InaZ protein and InaZ protein enhanced E.coli membranes. http://www.pnas.org/content/83/19/7256.full.pdf.

Include some current research, with at least one figure showing data.

Ecological Implications of
P.syringae Bioprecipitation

Fig 4. The “Nitrogen Triangle” breaking down the three major parts of the nitrogen cycle. Also the important molecules at each step are included. http://slideplayer.com/slide/7448073/.

Include some current research, with at least one figure showing data.

References

Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2016, Kenyon College.