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Robert Mclean, Ph.D.

 Department of Biology

Dr Robet McLean

Robert McLean

Regents' Professor

Phone: 512-245-3365

Fax: 512-245-8713



Mailing Address

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):

With Debby Siegele , Department of Biology, Texas A&M University , Fall 2000

With Marvin Whiteley, Molecular Genetics & Microbiology, University of Texas, Spring 2008

Memberships in Scientific Societies

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

Research Interests

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 SiegeleClay 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 Payload patch for shuttle flight STS-95future 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 Columbia picture showing payload behind astronaut Kalpana Chawlaexperiment on shuttle flight STS-107 , which STS-107 Mission Patchlaunched 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 , , . 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.

Courses Taught

BIO 4445/5445: Pathogenic Microbiology


BIO 4447/7447: Microbial Physiology and Genetics




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.


Theses Directed

  1. S Pringle 2014. “The effect of indole production on the growth of Escherichia coli when co-cultured with Enterococcus faecalis”  MS Thesis, Texas State University
  2. AJ Dumanski 1992 “Isolation and Characterization of the Capsule of Proteus mirabilis and its Role in Kidney Stone Formation”. MSc thesis, Queen's University
  3. MK Koenig 1996. “Parameters Affecting the Conformation of N-acetylneuraminic acid, Escherichia coli K1 Capsular Polysaccharide” MS thesis, Southwest Texas State University

  4. M Whiteley 1997 “Effects of Nutrient Limitation and Species Composition on Biofilm Development and Susceptibility to Iodine Disinfection”. MS thesis, Southwest Texas State University

  5. PT Khu 1998. “Bacterial Precious Metal Recovery”. MSc (Eng.) thesis, Queen's University (co-supervised with W-T Yen, Mining Engineering, Queen's University)

  6. HC Knowles 1998. “The Isolation, Culturing, and Characterization of Nannobacteria” MS thesis, Southwest Texas State University

  7. JL Adams 1998. “Role of rpoS in the Formation and Physiology of Escherichia coli Biofilms" MS thesis, Southwest Texas State University

  8. S Prabhakaran 1999. “Investigation of Bacterial Fragmentation as a Possible Origin of Nanobacteria” MS thesis, Southwest Texas State University

  9. GJ Balzer 2000. “Effect of relA and spoT Deletions on Escherichia coli Biofilm Formation” MS thesis, Southwest Texas State University

  10. MK Windham 2001. “Acyl Homoserine Lactone Recruitment of Bacteria Into Biofilms” MS thesis, Southwest Texas State University

  11. KL Fuson 2002. “Biofilm-Induced Gene Expression in Chemostat Grown Escherichia coli as Determined by a Gene Array” MS thesis, Southwest Texas State University

  12. CL Bates 2004. “Differential Gene Expression and Colanic Acid Gene Effects on Biofilm Formation” MS Thesis, Texas State University

  13. AK Welsh 2005. “Detection of an Introduced Bacterial Culture in Greywater Treatment Reactors” MS Thesis, Texas State University

  14. MM Merchant 2005. “Identification and Characterization of Bacterial Isolates from Spring Lake, Texas”  MS Thesis, Texas State University

  15. 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

  16. MM Weber 2007.  "Role of yjfO, agaB and atoS in Escherichia coli Biofilm Formation and Stress Response"  MS Thesis, Texas State University

  17. S Nath 2009.  “Potential Of Biofilms To Harbor Largemouth Bass Virus (LMBV)”  MS Thesis, Texas State University

  18. AA Taylor 2010. “Carbon And Clay Nanoparticles Provoke Numerous Responses in Salmonella enterica var. typhimurium and Escherichia coli” MS Thesis, Texas State University

  19. T R Zere 2011. “Indole and cAMP Promote Escherichia coli Survival in Mixed Culture” MS Thesis, Texas State University

  20. N Deb Adhikary 2011.  “Long term competition in Escherichia coli and Pseudomonas aeruginosa co-culture”  MS Thesis, Texas State University

  21. B Hidalgo-Romano 2013 “Indole Inhibition of AHL-Mediated Quorum Signaling Is Widespread in Gram-Negative Bacilli” MS Thesis, Texas State University-San Marcos

  22. 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

Students, Research Associates & Postdocs (the Slime Gang)  

2010 picture

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)


Lab photo 2011


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)



  • Marwa Al Tammemi, Grad Student (MS)
  • Benjamin Hidalgo-Romano, Grad Student (MS)
  • Leigh Maberry, Undergraduate
  • Christopher Munoz, Undergraduate
  • Ashley Orr, Undergraduate
  • Ernie Valenzuela, Grad Student (MS)
  • Logan Warren, Undergraduate


Postdoc:   None

Visiting Scientists: None

Honorary Lab Members:

Slime Gang Alumni


  • Weihua Chu, China Pharmaceutical University, Nanjing China, visiting professor and postdoc, 2009-2010

Graduate Students:

  • Anita Dumanski, 1992
  • Tony Persaud (co-supervised with D Beauchemin and HE Jamieson , Queen's University), 1994
  • Peter Vincent (co-supervised with M Sayer , Queen's University ), 1995
  • Mary Kay Koenig, 1996
  • Tati Schoeneweis, 1996
  • Marvin Whiteley , 1997
  • Peter Khu (co-supervised with W.T. Yen, Queen's University), 1998
  • Heidi Knowles, 1998
  • Jennifer Adams-Krumins, 1998
  • Leslie Harper, 1998
  • LJ Smith, 1999
  • Sabitha Prabhakaran, 1999
  • Brian Corbin (co-supervised with G Aron , SWT), 2000
  • Jim Jankowski (co-supervised with S West , SWT), 2000
  • Grant Balzer, 2000
  • Maricela Arias-Cantu, 2000
  • Katy Windham, 2001
  • Kerry Fuson, 2002
  • Christa Bates, 2004
  • Mubina Merchant, 2005
  • Allana Welsh, 2005
  • Pejmon Afshar, 2006
  • Will Boswell, 2007
  • Mary Weber, 2007-9
  • Maria Jimenez, 2007-8
  • Shubhankar Nath, 2009
  • Sarah Larocca, 2010
  • Alicia Taylor, 2010
  • Nihar Deb Adhikary, 2011
  • Tesfalem Zere, 2011
  • Ayme Cardwell, 2011


Undergraduate Students:

  • Lauren Bickerton, 1991 (co-supervised with D Beauchemin , Queen's University )
  • Alison Campbell, 1992 (co-supervised with D Beauchemin , Queen's University )
  • Dennis McCarty, 1994
  • Robert Routh, 1994
  • Pamela White, 1995
  • Kristi Dunn (co-supervised with G Upchurch , SWT), 1995
  • Denise Andrewartha, 1995
  • Erica Hughes, 1996
  • Hilary Bates, 1996
  • Erin Brown, 1996
  • Heather Larson, 1997
  • Amy Primmer, 1999
  • Gregg Bean, 1999
  • Matt Garner, 2000
  • Angela Roth, 2000
  • Elizabeth Pham, 2002
  • Christa Bates, 2002
  • April Czermerys, 2003
  • Cory Potts, 2003
  • Melanie Leal, 2004
  • Toni Sanger, 2004
  • Vanessa Pearson, 2004
  • Chris McGowin, 2004
  • Julie Frost, 2005
  • Olivia Gamez, 2005
  • Patricia Zenker, 2005
  • Sandy Bryant, 2006
  • Natalie Coldeway, 2006
  • Becky Fling, 2006
  • Jennifer Hamil, 2006
  • Aparna Mamidi, 2006
  • Monte Gomez, 2006
  • Megan Banning, 2007
  • Heath Keel, 2007
  • Veronika Huerta, 2007
  • Amani Khamis, 2007
  • Amani Zayed, 2007
  • Katie Mallet, 2007
  • Jaqueline Rohan, 2008
  • Gabriel Ortiz, 2008
  • Lindsey Wiggins, 2008
  • Mercy Dehart, 2008
  • James May, 2008
  • Tyler Cole, 2009
  • Maggie Maido, 2009
  • Carlos Perez, 2009-2010
  • Amanda Duran, 2010-2011
  • Sherille Bradley, 2010-2011
  • Jared Korn, 2011
  • Kourtney Applegate, 2011-2012
  • Jimmy Gollihar, 2011-2012


Technicians and Lab Visitors:

  • David Stickler, Cardiff University , UK , 1997
  • Eric Weaver, 1998
  • Ken Jacques, 1998 (Science Math Technology Education Institute - SMTEI)
  • "Slimey Biohunters" (Brent Krause, Justin Franke, Thomas Sanchez, Keri Mounger and Kristen Scott, Travis Middle School, Port Lavaca TX); Keller Tiemann, Malcolm McLean, and Alistair McLean, from Wimberley TX [elementary students who helped with the shuttle biofilm experiment], 1998
  • Katie Propst, (Nanobacteria science fair project, Merino High School , CO ) 1999
  • Nancy Perkins (SMTEI co-supervised with G Aron , SWT), 1999
  • Karen Wilkes, 1999 (SMTEI)
  • Tricia Parker (co-supervised with JMH Teichman, UT Health Sciences Center at San Antonio ), 1999
  • Ramon Madred (Martian Life science fair project, Canyon Middle School, New Braunfels, TX) 1999
  • Anna Razatos , 1999 (Honorary Slime Gang Alumna and former PhD student with G Georgiou, University of Texas )
  • Aaron Olmos (NIH Bridges Program), 2000
  • Tim Nealon, St. Phillip's College, 2000
  • Donna Bocanegra (NIH Bridges Program), 2001
  • Kim Martin (NIH Bridges Program), 2001
  • Bob Furtado, Teacher at Westlake High School, Austin TX - SMTEI, 2002.  We are saddened by the untimely passing of RL (Bob) Furtado on July 7, 2002. Bob taught for a number of years at Anderson High School in Austin and more recently at Westlake High School in Austin TX. He will be remembered for his boundless enthusiasm for science and pursuing scientific discoveries, as well as his dedication to his students.
  • Adriana Thrasher, NASA Johnson Space Center , 2002
  • Victoria Castro, NASA Johnson Space Center , 2002
  • Sandra Becerra (NIH Bridges Program), 2002
  • Geronimo Cortez (NIH Bridges Program), 2002
  • Shanika Glenn (NIH Bridges Program), 2002
  • Pamela Hathorn, formerly Midwestern State University , 2002-2003
  • Becky Sink, Midwestern State University , 2002-2003
  • Mary Barnes, 1995-2004. We were really sad to lose Mary as she has been an integral part of our lab for 10 years. We wish Mary, Paul, and their family all the best in their new home in New Orleans.
  • Jarah Meador, 2004 (Honorary Slime Gang Alumna and former PhD student with David Mitchell, MD Anderson Research Park)
  • Sue Reilly, 2004
  • James Neece, 2005
  • Richard Romeo - MacArthur High School, San Antonio, TX 2005
  • Nora Sabbuba, Postdoc with David Stickler, Cardiff University, UK, 2007
  • Stephanie Craig (Honorary Slime Gang Alumna and former Ph.D. student with Shelley Payne, University of Texas ), 2008
  • Daniel Willis, Rice University, summer 2010.