Module 3 SLP - microbial metabolic and environmental growth - Essay Example

Environmental Factors Affecting Microbial Growth: Comparing Lactobacillus bulgaricus from Escherichia coli The maintenance of metabolic functionsto sustain microbial growth is greatly affected by environmental factors such as temperature, pH, nutrient availability, aeration, and the like (Hogg, 2005; Brooks et al., 2007). Since bacterial species are ubiquitous and exhibit different biochemical characteristics, it is not surprising to discover that each species possesses a different set of optimum growth requirements (Brooks et al.

, 2007; Richard et al., 2007). This paper aims to present the differences in environmental factors that affect the growth of Lactobacillus bulgaricus and Escherichia coli.Temperature Different microbial species present varying degrees of thermal stability of its proteins and enzymes (Brooks et al., 2007). Hence, microorganisms display different temperature ranges that are optimal for their growth and metabolism. Those organisms which grow best at low temperatures (15-20 OC) are called psychrophiles.

Mesophylic groups grow best at 30-37 OC while thermophilic forms grow best at a temperature range of 50-60 OC. According to a study conducted by Radke-Mitchell and Sandine (1986), L. bulgaricus has an optimum growth temperature range of 43-46 OC. On the other hand, E coli grows best at 37 OC, similar to the normal body temperature (Don, 2008). This is not surprising because E. coli forms a part of the body’s normal bacterial flora (Don, 2008).pH The significance of maintaining a certain range of pH for bacterial metabolism and growth is demonstrated by the fact that hydrogen ion concentration influences the integrity and functions of proteins, and other biochemical processes (Campbell and Reece, 2004).

The acidity and alkalinity of the environment also affects the availability of nutrients essential for the growth of microorganisms. Those species that grow best at a pH range of 6.0-8.0 are called neutralophiles. Meanwhile, microorganisms with optimum pH growth of 3.0 or lower are classified as acidophiles while those with optima at a pH of 10.5 or higher are called alkaliphiles (Brooks et al., 2007). Beal et al. (2009) reported that L. bulgaricus achieve its highest biomass in culture when maintained at pH 5.0. Cell viability was also noted to be at its peak at pH 5.

0 (Beal et al., 2009). On the other hand, the optimum pH for growth of E. coli is 6.0-8.0 (York et al., 1984).Oxygen The process of energy production, termed respiration, operates by virtue of electron acceptors. Oxygen serves as an electron acceptor in bacterial respiration (Brooks et al., 20097). Organisms which strictly require oxygen for its growth are called obligate anaerobes. Those that can proliferate with or without oxygen are called facultative aerobes while microorganisms that cannot grow in the presence of oxygen are called obligate anaerobes (Brooks et al., 2007). L.

bulgaricus is a facultative anaerobe. Similarly, E. coli is capable of aerobic respiration in the presence of oxygen and fermentation of sugars in anaerobic conditions (Hogg, 2005).Salinity Depending on the natural habitat of the organism, some may require sodium chloride for optimum growth. These organisms are called halophiles. Mild halophiles are characterized as those species requiring 1-6% salt while extreme halophiles are those that require 15-30% NaCl (Todar, 2009). However, some microorganisms are capable of growing in mildly salty environments although they proliferate best in salt-free conditions (Todar, 2009).

These microorganisms are characterized as halotolerant. In a study conducted by Wheater (1955), it was established that L. bulgaricus does not require NaCl to grow. In fact, the study suggested that NaCl appears to inhibit the growth of L. bulgaricus in in vitro cultures. On the contrary, Hrenovic and Ivankovic (2009) reported that E. coli can grow in nutrient broth supplemented with up to 5% NaCl. Carbon Source Microorganisms require organic carbon in a form that can be readily assimilated for the biologic synthesis of molecules necessary for growth.

Hence, the type of carbon source present in the environment greatly affects bacterial growth and metabolism. According to Hempfling and Mainzer (1975), E. coli can utilize glucose, cyclic adenosine monophosphate (cAMP), galactose, mannitol, L-glutamate, glycerol, succinate, and acetate as carbon sources. However, it was observed that glucose provides the best carbon source for the growth of E. coli (Hempfling and Mainzer, 1975). On the other hand, the carbon sources that L. bulgaricus can utilize efficiently appears to be limited to sugars.

Specifically, L. bulgaricus can utilize glucose, galactose, lactose, fructose and mannose as carbon sources (Wheater, 1955). Lactose offers the best carbon source for L. bulgaricus based on the study conducted by Wheater (1955).References:Radke-Mitchell, L., and sandine, W. 1986. Influence of temperature on associative growth of Streptococcus thermophilus and Lactobacillus bulgaricus. J Dairy Sci. 69(10):2558-68.Beal, C., Rault, A., and Bouix, M. 2009. Fermentation pH influences the dynamic of Lactobacillus bulgaricus CFL1 physiological state during pH-controlled cultures. Appl. Environ.

Microbiol. doi:10.1128/AEM.02725-08Don, S. 2008. Optimal conditions for the growth of E. coli. Accessed at: http://www.scribd.com/doc/11337868/Optimal-Conditions-for-the-Growth-of-E-Coli. Date accessed: May 10, 2012York, N., Doyle, M., and Schoeni, J. 1984. Characteristics of E. coli. Accessed at http://www.hi-tm.com/1908/SECTION-2-D-1908.pdf. Date accessed: May 10, 2012Todar, K. 2009. Lectures in Microbiology: University of Wisconsin-Madison. Accessed at: http://textbookofbacteriology.net/themicrobialworld/nutgro.html. Date accessed: May 11, 2012.

Hrenovic, J., and Ivankovic, T. 2009. Survival of Escherichia coli and Acinetobacter junii at various concentrations of sodium chloride. EurAsia J BioSci. 3:144-151 Wheater, D. 1955. The Characteristics of Lactobacillus acidophilus and Lactobacillus bulgaricus. J . gen. Microbiol. 12:123-132.Hempfling, W., and Mainzer, S. 1975. Effects of Varying the Carbon Source Limiting Growth on Yield and Maintenance Characteristics of Escherichia coli in Continuous Culture.Journal of Bacteriology. pp.

1076-1087Brooks, G., Butel, J., and Morse, S. 2007. Jawetz, Melnick and Adelbergs Medical Microbiology. 24th ed. The McGraw-Hill Companies, Inc. Ch5Hogg, S. 2005. Essential Microbiology. John Wiley & Sons Ltd. Chichester, England.pp 187-189Campbell, N., and Reece, Jane. 2004. Biology. 6th ed. Peason Education South Asia PTE LTD. Jurong, Singapore. Pp. 47-48