Department of Biology
Texas State University
601 University Drive
San Marcos , TX 78666
B.Sc. Microbiology, University of Guelph , 1978
Ph.D. Microbiology, with JW Costerton, University of Calgary , 1986
Postdoc with TJ Beveridge, University of Guelph , 1986 - 1988
Developmental Leave (Sabbatical):
American Society for Microbiology
Texas Branch, American Society for Microbiology (Region Planning Coordinator for ASM region 6 (2007-2009), covering Missouri Valley, Rio Grande, Rocky Mountain, and Texas ASM branches)
Sigma Xi Scientific Research Society
Biofilms: Most bacteria in their natural environments live on surfaces as slime-encased, biofilm communities. In contrast to their planktonic counterparts, sessile bacterial populations are significantly more resistant (by several orders of magnitude) to environmental stresses such as harmful chemicals, antibiotics and predation. While biofilms are the dominant form of growth of bacteria in nature, little is known about the biological factors that allow growth as biofilms. Studies in my lab, done in collaboration with Debby Siegele, Clay Fuqua , Walt Fast, Dhiraj Vattem, and Sandy Pierson , address three major aspects of bacterial physiology which are important in biofilm growth and development. These include the ability of individual bacteria to grow slowly, survive starvation stresses, express a variety of biofilm-activated genes, and for the organisms within a biofilm community to perform many metabolic activities as a group through a phenomenon known as quorum-sensing. Recently in collaboration with Marvin Whiteley and Tom Wood, we have expanded these studies by employing gene arrays and transcriptional profiling to investigate overall patterns of gene expression in mixed culture bacterial biofilms.
Bacteria in nature, including those within biofilms, live as mixed populations. Therefore in order to understand natural biofilm growth, it is important to investigate microbial interactions in mixed communities. We have observed that bacterial community composition affects biofilm formation and susceptibility to iodine disinfection ( link to abstract ), and have just shown that E. coli indole production promotes its growth in mixed culture with Pseudomonas aeruginosa by inhibiting quorum signaling (link to abstract), and are now investigating whether quorum-sensing and other physiological activities affect biofilm community structure.
Aside from their importance on earth, biofilms may also impact the success of future long-term space flights due to possible fouling of water recycling filters. We recently flew an experiment in the John Glenn space shuttle (STS-95 ) to show that the bacterium, Pseudomonas aeruginosa, could form biofilms under weightless conditions. In a follow-up experiment, we flew an experiment on shuttle flight STS-107 , which launched on January 16, 2003 to study biofilm formation and microbial competition in a three-member bacterial consortium. On February 1 2003 , during reentry, the space shuttle Columbia was destroyed along with all crew members . These include Commander Rick Husband, Pilot William McCool, Payload Commander Michael Anderson, Mission Specialist David Brown, Mission Specialist Kalpana Chawla, Mission Specialist Laurel Clark, and Payload Specialist Ilan Ramon. We mourn the loss of these seven outstanding people and offer our thoughts and prayers for their families and friends. Appended is a photograph taken aboard Columbia during STS-107, showing Astronaut Kalpana Chawla with our payload visible in the upper left corner. Amazingly, our payload survived the impact and we gained access to it during the week of May 5, 2003. Some images can be seen at http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=19550 , http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=19539 , http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=19475 . We have found one organism in the payload that may have survived this disaster (McLean et al., Icarus 181: 323-325, 2006) (link to abstract).
Microbial Mineral formation and nanobacteria: Bacteria and other microorganisms have been associated with the formation of many types of sedimentary rocks and minerals. Recently, small bacteria-shaped objects have been described by RL Folk, a geologist at the University of Texas . While these objects resemble bacteria, they are approximately 1/5 the size and have thus been termed nanobacteria also spelled nannobacteria). Although initially thought to be independant life forms, our current thinking is that they are more likely to represent remnants of bacterial polymers (slime) and possibly outer membrane vesicles. Aside from their potential importance in geology, they have also been cited as evidence of extraterrestrial life on a recently described Martian meteorite. Nanobacteria research in my lab, in association with Robert L Folk (Geological Sciences , University of Texas ) and Brenda L Kirkland (Geosciences , Mississippi State University ) seeks to ascertain the nature of nanobacteria and to investigate whether they are involved in mineral formation.
BIO 4445/5445: Pathogenic Microbiology
BIO 4447/7447: Microbial Physiology and Genetics
SELECTED PUBLICATIONS (2010 - present):
Weber MM, CL French, MB Barnes, DA Siegele, and RJC McLean. 2010. A previously uncharacterized gene, yjfO (bsmA) influences Escherichia coli biofilm formation and stress response. Microbiology 156: 139-147.
Nath S., GM Aron, GM Southard, and RJC McLean. 2010. Potential for largemouth bass virus to associate within and gain protection from bacterial biofilms. J. Aquat. Anim. Health 22: 95-101.
McLean RJC and MAC McLean. 2010. Microbial survival mechanisms of relevance to panspermia. J. Cosmology 7: 1802-1820.
McLean RJC 2010. Planetary protection and missions between Earth and Mars. J. Cosmology 12: 3842-3845.
Dusane DH, SS Zinjarde, VP Venugopalan, RJC McLean, MM Weber, PKSM Rahman 2010. Quorum sensing: implications on rhamnolipid biosurfactant production. Biotechnol. Genetic Eng. Rev. 27: 159-184.
Kay MK, TC Erwin, RJC McLean, and GM Aron. 2011. Bacteriophage ecology in Escherichia coli and Pseudomonas aeruginosa mixed biofilm communities. Appl. Environ. Microbiol. 77: 821-829.
Chu, W, TR Zere, MM Weber, TK Wood, M Whiteley, B Hidalgo-Romano, E. Valenzuela, and RJC McLean. 2012. Indole production promotes Escherichia coli mixed culture growth with Pseudomonas aeruginosa by inhibiting quorum signaling. Appl. Environ. Microbiol. 78: 411-419.
McLean RJC, JS Lam, and LL Graham. 2012. Training the biofilm generation – a tribute to JW Costerton. Journal of Bacteriology 194: 6706-6711. (featured on the cover of JB)
Taylor, AA, SA Bryant, and RJC McLean. 2013. Overcoming the challenges associated with laboratory preparation with the help of students. Journal of College Science Teaching 43: 10-11.
McLean RJC and SL Pringle. 2013. Identifying bacterial menu choices from the host buffet during infections. Journal of Bacteriology 195: 4989-4990.
McLean RJC and KS Kakirde. 2013. Enhancing metagenomics investigations of microbial interactions with biofilm technology. Int. J. Mol. Sci. 14: 22246-22257
Taylor AA, GM Aron, GW Beall, N Dharmasiri, Y Zhang, and RJC McLean. 2014. Carbon and clay nanoparticles induce minimal stress responses in Gram negative bacteria and eukaryotic fish cells. Environ. Toxicol. 29: 961-968.
Vega LM, PJ Alvarez, and RJC McLean. 2014 Bacterial signaling ecology and potential applications during biofilm construction. Microb. Ecol. 68: 24-34.
McLean RJC. 2014. Normal bacterial flora may inhibit Candida albicans biofilm formation by autoinducer-2. Front. Cell. Infect. Microbiol. 4:117. doi: 10.3389/fcimb.2014.00117
Vega LM, J Mathieu, Y Yang, BH Pyle, RJC McLean, and PJ Alvarez. 2014 Nickel and cadmium, ions inhibit quorum sensing and biofilm formation without affecting viability in Burkholderia multivorans. Intern. Biodeterior. Biodegrad. 91: 82-87.
Hidalgo-Romano B, J Gollihar, SA Brown, M Whiteley, E Valenzuela Jr, HB Kaplan, TK Wood, and RJC McLean. 2014. Indole Inhibition of AHL-Mediated Quorum Signaling Is Widespread in Gram-Negative Bacteria. Microbiology, in press.
BOOK CHAPTERS (2010 - present):
Chu W, DA Vattem, V Maitin, MB Barnes, and RJC McLean. 2011. Bioassay of quorum sensing compounds using Chromobacterium violaceum and Agrobacterium tumefaciens. In: K Rumbaugh (ed) Quorum Sensing Methods and Protocols, Methods in Molecular Biology Series vol 692, Humana Press, chapter 1.
McLean RJC and BL Kirkland. Nanostructures and nanobacteria. 2013. In LL Burton (ed), Nanomicrobiology: Physiological and Environmental Characteristics, Springer Verlag, Berlin.
MK Koenig 1996. “Parameters Affecting the Conformation of N-acetylneuraminic acid, Escherichia coli K1 Capsular Polysaccharide” MS thesis, Southwest Texas State University
M Whiteley 1997 “Effects of Nutrient Limitation and Species Composition on Biofilm Development and Susceptibility to Iodine Disinfection”. MS thesis, Southwest Texas State University
PT Khu 1998. “Bacterial Precious Metal Recovery”. MSc (Eng.) thesis, Queen's University (co-supervised with W-T Yen, Mining Engineering, Queen's University)
HC Knowles 1998. “The Isolation, Culturing, and Characterization of Nannobacteria” MS thesis, Southwest Texas State University
JL Adams 1998. “Role of rpoS in the Formation and Physiology of Escherichia coli Biofilms" MS thesis, Southwest Texas State University
S Prabhakaran 1999. “Investigation of Bacterial Fragmentation as a Possible Origin of Nanobacteria” MS thesis, Southwest Texas State University
GJ Balzer 2000. “Effect of relA and spoT Deletions on Escherichia coli Biofilm Formation” MS thesis, Southwest Texas State University
MK Windham 2001. “Acyl Homoserine Lactone Recruitment of Bacteria Into Biofilms” MS thesis, Southwest Texas State University
KL Fuson 2002. “Biofilm-Induced Gene Expression in Chemostat Grown Escherichia coli as Determined by a Gene Array” MS thesis, Southwest Texas State University
CL Bates 2004. “Differential Gene Expression and Colanic Acid Gene Effects on Biofilm Formation” MS Thesis, Texas State University
AK Welsh 2005. “Detection of an Introduced Bacterial Culture in Greywater Treatment Reactors” MS Thesis, Texas State University
MM Merchant 2005. “Identification and Characterization of Bacterial Isolates from Spring Lake, Texas” MS Thesis, Texas State University
WT Boswell 2007. "Effects of N-acyl-L-homoserine lactone lactonase on disruption of preformed biofilms, bacterial recruitment, and prevention of biofilms" MS Thesis, Texas State University
MM Weber 2007. "Role of yjfO, agaB and atoS in Escherichia coli Biofilm Formation and Stress Response" MS Thesis, Texas State University
S Nath 2009. “Potential Of Biofilms To Harbor Largemouth Bass Virus (LMBV)” MS Thesis, Texas State University
AA Taylor 2010. “Carbon And Clay Nanoparticles Provoke Numerous Responses in Salmonella enterica var. typhimurium and Escherichia coli” MS Thesis, Texas State University
T R Zere 2011. “Indole and cAMP Promote Escherichia coli Survival in Mixed Culture” MS Thesis, Texas State University
N Deb Adhikary 2011. “Long term competition in Escherichia coli and Pseudomonas aeruginosa co-culture” MS Thesis, Texas State University
B Hidalgo-Romano 2013 “Indole Inhibition of AHL-Mediated Quorum Signaling Is Widespread in Gram-Negative Bacilli” MS Thesis, Texas State University-San Marcos
M Altameemi 2013. “Method development for exploring probiotic-host interaction in a Caenorhabditis elegans model” (co-supervised with V. Maitin, Dept. Family and Consumer Sciences, Texas State University) MS Thesis, Texas State University
Slime Gang 2010
L-R: Bob McLean, Sarah Larocca, Sherille Bradley, Alicia Taylor, Ashley Orr, Chris Munoz, Tesfalem Zere, Nihar Deb Adhikary, Weihua Chu. (Missing: Amanda Duran, Carlos Perez)
Slime Gang (Spring 2011):
L-R: Amanda Duran, Nihar Deb Adhikary, Ernie Valenzuela, Tesfalem Zere, Ben Hidalgo-Romano, Bob McLean, Chris Munoz, Ashley Orr, Kourtney Applegate, Sherille Bradley, (Missing Ayme Cardwell)
Visiting Scientists: None
Honorary Lab Members:
Slime Gang Alumni
Technicians and Lab Visitors: