Previous Article | Next Article 
Applied and Environmental Microbiology, July 2002, p. 3644-3650, Vol. 68, No. 7
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.7.3644-3650.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Phylogenetic Relationships and Coaggregation Ability of Freshwater Biofilm Bacteria
Alex H. Rickard,1 Stephen A. Leach,2 Laurence S. Hall,1 Clive M. Buswell,2 Nicola J. High,1 and Pauline S. Handley1*
School of Biological Sciences, University of Manchester, Manchester,1
Centre for Applied Microbiology and Research, Salisbury, Wiltshire, United Kingdom2
Received 7 December 2001/
Accepted 21 March 2002

ABSTRACT
Nineteen numerically dominant heterotrophic bacteria from a
freshwater biofilm were identified by 16S ribosomal DNA gene
sequencing, and their coaggregation partnerships were determined.
Phylogenetic trees showed that both distantly related and closely
related strains coaggregated at intergeneric, intrageneric,
and intraspecies levels. One strain,
Blastomonas natatoria 2.1,
coaggregated with all 18 other strains and may function as a
bridging organism in biofilm development.

INTRODUCTION
Coaggregation between bacteria occurs when two or more genetically
distinct strains interact by specific cell-cell recognition
(
12). The phenomenon was first recognized between different
oral plaque-forming bacteria, where both intergeneric and intrageneric
coaggregation occurs (
11). Coaggregation also occurs between
bacteria isolated from a freshwater biofilm (
3,
19), and it
has been suggested that coaggregation may also mediate in the
sequential integration of species of bacteria into freshwater
biofilms (
8,
20). Recently, Rickard et al. (
19) used partial
16S rRNA gene sequencing to identify four coaggregating strains
of
Blastomonas natatoria and one strain of
Micrococcus luteus from an established freshwater biofilm community (
3). Six coaggregation
partnerships between these five strains were found and shown
to be mediated by growth-phase-dependent lectin-saccharide interactions
(
19). These five coaggregating strains of
B. natatoria and
M. luteus were part of a larger community of 19 coaggregating strains
that were all isolated simultaneously from a biofilm formed
on glass in a chemostat (
3). The identities of the other members
of the consortium are unknown, and the extent of intergeneric
and intrageneric and intraspecies coaggregation between all
members of the community has not been analyzed previously. Since
coaggregation may be an adhesion mechanism involved with integrating
and establishing bacteria in the biofilm community, it is important
to know the extent of this specific adhesion mechanism in the
freshwater biofilm. It is also relevant to know how closely
related coaggregating strains are, since this has implications
for understanding the biodiversity of the biofilm community.
Therefore, the work reported here had three main objectives:
(i) identification by 16S rRNA gene sequencing of all strains
in the freshwater biofilm community; (ii) construction of phylogenetic
trees by the computation of evolutionary distance matrices and
maximum-likelihood rooted dendrograms; and (iii) analysis of
intergeneric and intrageneric and intraspecies (interstrain)
coaggregation partnerships between members of the biofilm community
deduced using the phylogenetic trees.
All strains used in this study were isolated from a 14-day-old biofilm on a glass coupon in a two-stage chemostat kept at 4°C, which was initially inoculated with water from a borehole water source (Porton borehole, Salisbury, United Kingdom) (3). The ionic composition of the water and temperature within the chemostat were very similar to the conditions found in the source borehole water (4). Strains from the biofilm were initially grown on R2A agar (17) and were inoculated separately into conical flasks (250 ml) containing 100 ml of R2A broth and shaken at 200 rpm at 25°C in a G20 orbital shaker (New Brunswick Scientific, New Brunswick, N.J.).
The strains were identified by the method of Rickard et al. (19). Approximately 650 bases of the 16S rRNA gene were sequenced. Amplification of 16S ribosomal DNA was performed by removing a single bacterial colony from R2A agar plates to provide template DNA. Partial 16S rRNA gene sequences corresponding to the Escherichia coli 16S ribosomal DNA nucleotide positions 8 to 806 were amplified and sequenced using the universal primers 8FPL (22) and 806R (23). Partial 16S rRNA gene sequences of each of the strains were initially compared to those in the databases by using the FASTA3 program, and unambiguous positions of representative sequences were then aligned by using CLUSTALX version 1.64b (21). Maximum-likelihood analysis was conducted using DNAML (6), and the trees were viewed using TREEVIEW (15).
Table 1 shows the percent nucleotide sequence identity of all 19 biofilm strains to the closest sequence in the EMBL database. The five strains identified by Rickard et al. (19) have been included for completeness. Eleven of the fourteen strains identified in this study could be assigned to a genus, but no species identification was possible, since the closest strains in the database were not assigned species (Table 1). The biochemical and morphological characteristics of each strain supported the assigned identities (data not presented). Only strain 2.17 could not be identified to the genus level, since it had a very low percent sequence identity (87.6%) with the closest matching 16S rRNA gene sequence in the database, which belonged to Salinicoccus roseus (EMBL accession no. SR16SRRN1).
View this table:
[in this window]
[in a new window]
|
TABLE 1. Identification of the aquatic biofilm strains by alignment with the sequences of organisms in the EMBL database
|
Maximum-likelihood phylogenetic trees inferred from the 16S
rRNA sequences of all the 19 coaggregating biofilm strains showed
that they are distributed over a wide range of bacterial taxonomic
groups (Fig.
1 and
2). The 6 gram-negative genera are distributed
between four groups of the alpha-
Proteobacteria subclass of
the
Proteobacteria: the
Zymomonas,
Methylobacterium,
Bradyrhizobium,
and
Rhodobacter groups, as well as a single group of the gamma-
Proteobacteria subclass, the
Pseudomonas group (Fig.
1). The two gram-positive
genera,
Micrococcus and
Nocardiodes, were members of the high-G+C
groups
Micrococcaceae and
Propionibacterineae (Fig.
2). Strain
2.17, which could not be identified, is not on the gram-positive
phylogenetic tree but is a member of the low-G+C group occupied
by
S. roseus.
Most of the identified strains in this study were from the alpha-
Proteobacteria (74%), and no beta-
Proteobacteria were found. R2A agar has been
shown to support the growth of alpha and gamma
Proteobacteria rather than the less easily cultivable beta-
Proteobacteria (
9,
10). This could explain why the majority of these freshwater
biofilm strains that were originally isolated by Buswell et
al. (
3) were from the alpha-
Proteobacteria. However, the objective
of this study was to establish the extent of coaggregation between
cultivable heterotrophic bacteria, and enough strains have been
isolated and identified to reveal that coaggregation is a common
property of strains in this ecosystem. A considerable taxonomic
diversity of heterotrophs in the biofilm was found, and all
except strain 2.17 are very closely related to organisms that
have previously been isolated from freshwater or soil environments.
The phylogenetic trees revealed that the biofilm contained clusters of very closely related strains or clones. These clonal groups included five B. natatoria strains, four Sphingomonas strains, two Methylobacterium strains (Fig. 1), and two Nocardioides strains (Fig. 2). Each clonal group contained strains with different coaggregation partners (see Fig. 5). It has been proposed that biofilms can act as reservoirs of clones of the same species and that this may enhance the survival of the species during environmental fluctuations (2, 16). It is not yet clear why closely related clones with such distinct coaggregation patterns can coexist within a freshwater biofilm.
In order to detect all the coaggregation partnerships between
strains, all 171 possible pairwise combinations of strains were
tested using the visual coaggregation assay originally developed
by Cisar et al. (
5) and adapted by Rickard et al. (
20). Because
the ability to coaggregate has been found to be optimum for
only a relatively short period in stationary phase and not to
occur in exponential phase for
B. natatoria 2.1 and
M. luteus 2.13 (
19), strains were harvested at three different times during
stationary phase. The harvest times were the following: early
stationary phase (36 h), mid-stationary phase (72 h), and later
stationary phase (144 h) in batch culture (growth kinetics data
not shown). In this way the optimum time in stationary phase
at which coaggregation occurred could be determined. Cells were
harvested and washed three times in sterile deionized water.
Using a spectrophotometer (Cecil instruments, Cambridge, United
Kingdom), the washed cells were then resuspended in deionized
water to an optical density at 650 nm (OD
650) of 1.0 and concentrated
to give a calculated final OD
650 of 1.5. For coaggregation,
pairs of strains were mixed at an OD
650 of 1.5 in equal volumes
(200 µl) at room temperature in 6- by 50-mm silica Durham
tubes (Scientific Lab Supplies, Nottingham, United Kingdom).
Mixtures were vortexed for 10 s, and the tubes were rolled gently
for 30 s. The degree of coaggregation between each pair was
scored as follows: 0, no coaggregates in suspension; 1+, small
uniform aggregates in a turbid suspension; 2+, easily visible
coaggregates in a turbid suspension; 3+, clearly visible coaggregates
which settle, leaving a clear supernatant; 4+, large flocs of
coaggregates that settle almost instantaneously, leaving a clear
supernatant. Control tubes of each isolate on its own were also
included to assess autoaggregation. Where present, the autoaggregation
score was deducted from the coaggregation score.
Maximum visual coaggregation scores for different pairs ranged from 1+ to 4+ (Fig. 3), and 82 pairs out of the total of 171 pairs (48%) gave a positive score. Scores were always reproducible after growth in batch culture for a set period of time, and three batches of all cultures were tested separately to confirm the reproducibility of coaggregation. For all pairs, a microscopic examination of the coaggregating pairs showed flocs of coaggregating cells and the size of the coaggregates increased with increasing visual coaggregation scores (Fig. 4).
In order to represent the complexities of the many coaggregation
partnerships, a matrix of all the pairings giving a score of
2+ or greater was constructed (Fig.
5). The growth time in batch
culture (36, 72, or 144 h) at which optimum coaggregation scores
occurred is indicated on the matrix. For 76 of the 82 coaggregating
pairs (93%) the ability to coaggregate was maximum at only one
of the three harvest times in stationary phase. After 36 h of
growth in batch culture, 38 pairs (22%) coaggregated, after
72 h, 62 pairs (36.2%) coaggregated, and after 144 h of growth,
36 pairs (21%) coaggregated. The majority of the possible coaggregation
partnerships occurred after incubation in batch culture for
72 h, although 7% of the possible 171 coaggregation partnerships
showed a consistent score which was not influenced by the harvest
time (Fig.
5). In freshwater the bacteria in biofilms are probably
in stationary phase for the majority of the time (
7) and may
therefore have evolved to express the ability to coaggregate
while in this starved physiological state.
As shown in the coaggregation matrix (Fig. 5), B. natatoria 2.1 was able to coaggregate with all other strains tested. Other highly interactive strains included Sphingomonas sp. strain 2.15, with 15 partner strains, and Afipia sp. strain 2.2, with 13 partner strains. In contrast, Pseudomonas sp. strain 2.19 and B. natatoria 2.4 had the lowest number of partnerships, each coaggregating with two and four partners, respectively. Each strain possessed different coaggregation abilities, with respect to numbers and identity of partners as well as the size of the flocs formed.
When considering the phylogenetic relationships and coaggregation partnerships, coaggregation at an intergeneric level was extremely common and every strain tested coaggregated intergenerically with at least one other strain from a different genus at a level of 2+ or greater (Fig. 5). For example, strain B. natatoria 2.1 coaggregated with strains from seven other generaSphingomonas, Nocardioides, Paracoccus, Methylobacterium, Micrococcus, Pseudomonas, and strain 2.17. Coaggregation at the interstrain (intraspecies) level was common, occurring between closely related strains of Sphingomonas and Blastomonas clustering in the same phylogenetic groups. Coaggregation between B. natatoria 2.1 and three other strains of B. natatoria (2.3, 2.8, and 2.6) has been reported previously (19); however, this study shows that B. natatoria 2.4 is a very poor coaggregator and it cannot coaggregate at the interstrain level with the other Blastomonas strains. Intergeneric coaggregation is common between oral bacteria (13), but intraspecies (interstrain) coaggregation has not yet been reported between plaque bacteria. Thus, intraspecies coaggregation may well be a characteristic that is unique to freshwater biofilm bacteria.
While intergeneric and interstrain coaggregations are common between these aquatic biofilm community members, there is only one example of intrageneric coaggregation. Sphingomonas 2.10 and Sphingomonas 2.15 coaggregate with each other after 144 h (Fig. 5) with a score of 4+, and the evidence indicates that they are likely to be from different, as yet unnamed species. First, the phylogenetic tree (Fig. 1) shows a cluster of very closely related Sphingomonas strains (2.11, 2.12, 2.15, and 2.18) with strain 2.10 in a separate subgroup. The group of four strains all have >99.1% sequence homology to each other and none were 100% identical. However, strain 2.10 had only from 97.7 to 98.4% sequence homology with the four closely related strains. Secondly, typing of the Sphingomonas strains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels of whole-cell proteins shows 20 visible protein bands for strain 2.10, while for the strains in the group of four, only five identical bands were visible (18). In addition, all the Sphingomonas strains possessed distinct colony and cell morphologies. Taken together, the evidence indicates that 2.10 is likely to be a different species from the other four Sphingomonas strains. Therefore, we propose that intrageneric coaggregation can occur in both aquatic and oral biofilms.
In dental plaque, Fusobacterium nucleatum can coaggregate with all other oral bacteria so far tested (1, 14) and has therefore been described as a "promiscuous" coaggregator which is proposed to have a very significant role as a bridging organism linking primary and secondary colonizers that cannot coaggregate with each other (11). Since B. natatoria 2.1 coaggregated with all 18 other biofilm strains, it may also be described as promiscuous. B. natatoria 2.1 may have a role equivalent to that of F. nucleatum in the development of this freshwater biofilm and may have the same role in other biofilms. It is not yet known whether colonization during freshwater biofilm formation involves a succession of primary and secondary colonizers, as occurs in the development of dental plaque. However, it is possible that highly coaggregating genera such as Blastomonas, Afipia, and Sphingomonas spp. could be quantitatively important members of freshwater biofilm communities and that their ability to adhere to other community members in a biofilm would give them a colonization advantage.
In conclusion, this study has revealed that intergeneric and intraspecies coaggregation between freshwater bacteria are common phenomena that occur between strains from a laboratory model aquatic biofilm. In addition, expression of coaggregation is dependent on cells being in the optimum physiological state for coaggregation, which usually occurs in stationary phase. It is therefore possible that since cells grow very slowly in nutrient-limited biofilms, a natural freshwater biofilm would provide suitable conditions for expression of coaggregation.

Nucleotide sequence accession numbers.
Partial 16SrRNA sequences for
M. luteus 2.13 and the four
B. natatoria strains (2.1, 2.3, 2.6, and 2.8) have been assigned
accession numbers previously (
19). The sequences of all the
remaining identified strains were also deposited in the EMBL
database. The EBML accession numbers of the sequences were the
following: for
Afipia sp. strain 2.2, accession no.
AJ299221;
for
B. natatoria 2.1, 2.3, 2.4, 2.6, and 2.8, accession numbers
AJ250434,
AJ250435,
AJ299222,
AJ250436, and
AJ250437, respectively;
for
Methylobacterium sp. strains 2.7 and 2.9, accession numbers
AJ299223 and
AJ299224, respectively; for
M. luteus 2.13, accession
number
AJ250438; for
Nocardioides sp. strains 2.14 and 2.17,
accession numbers
AJ299232 and
AJ299233, respectively; for
Paracoccus marcusii 2.21, accession no.
AJ299231; for
Pseudomonas sp. strain
2.19, accession no.
AJ299230; for
Sphingomonas sp. strains 2.10,
2.11, 2.12, 2.15, and 2.18, accession numbers
AJ299225,
AJ299226,
AJ299227,
AJ299228, and
AJ299229, respectively; for unknown
bacterial heterotroph 2.17, accession no.
AJ299234.

FOOTNOTES
* Corresponding author. Mailing address: University of Manchester, 1.800 Stopford Building, Oxford Rd., Manchester M13 9PT, United Kingdom. Phone: 44 (0)161 275 5265. Fax: 44 (0)161 275 5656. E-mail:
p.s.handley{at}man.ac.uk.


REFERENCES
1 - Andersen, R. N., N. Ganeshkumar, and P. E. Kolenbrander. 1998. Helicobacter pylori adheres selectively to Fusobacterium spp. Oral Microbiol. Immunol. 13:51-54.[Medline]
2 - Bowden, G. H. W. 1999. Oral biofilm an archive of past events? p. 211-235. In H. N. Newman and M. Wilson (ed.), Dental plaque revisited: oral biofilms in health and disease. Bioline press, Cardiff, United Kingdom.
3 - Buswell, C. M., Y. M. Herlihy, P. D. Marsh, C. W. Keevil, and S. A. Leach. 1997. Coaggregation amongst aquatic biofilm bacteria. J. Appl. Microbiol. 83:477-484.[CrossRef]
4 - Buswell, C. M., Y. M. Herlihy, C. W. Keevil, P. D. Marsh, and S. A. Leach. 1999. Carbon load in aquatic ecosystems affects the diversity and biomass of water consortia and the persistence of the pathogen Campylobacter jejuni within them. J. Appl. Microbiol. Symp. Suppl. 85:161S-167S.
5 - Cisar, J. O., P. E. Kolenbrander, and F. C. McIntire. 1979. Specificity of coaggregation reactions between human oral streptococci and strains of Actinomycetes viscosus or Actinomycetes naeslundii. Infect. Immun. 24:742-752.[Abstract/Free Full Text]
6 - Felsenstein, J. 1989. PHYLIP: Phylogeny Inference Package (version 3.2). Cladistics 5:164-166.
7 - Halda-Alija, L., and T. C. Johnston. 1999. Diversity of culturable heterotrophic aerobic bacteria in pristine stream bed sediments. Can. J. Microbiol. 45:879-884.[CrossRef][Medline]
8 - Handley, P. S., A. H. Rickard, S. A. Leach, C. M. Buswell, and N. J. High. 2001. Coaggregationis it a universal phenomenon? p. 1-10. In P. Gilbert, D. Allison, M. Brading, J. Verran, and J. Walker (ed.), Biofilm community interactions: chance or necessity? Bioline press, Cardiff, United Kingdom.
9 - Kalmbach, S., W. Manz, and U. Szewzyk. 1997. Isolation of new bacterial species from drinking water biofilms and proof of their in situ dominance with highly specific 16S rRNA probes. Appl. Environ. Microbiol. 63:4164-4170.[Abstract]
10 - Kämpfer, P., R. Erhart, C. Beimfohr, J. Böhringer, M. Wagner, and R. Amann. 1996. Characterisation of bacterial communities from activated sludge: culture-dependent numerical identification versus in situ identification using group- and genus-specific rRNA-targeted oligonucleotide probes. Microb. Ecol. 32:101-121.[Medline]
11 - Kolenbrander, P. E., R. N. Andersen, D. L. Clemens, C. J. Whittaker, and C. M. Klier. 1999. Potential role of functionally similar coaggregation mediators in bacterial succession. In H. N. Newman and M. Wilson (ed.), Dental plaque revisited: oral biofilms in health and disease, p. 171-186. Bioline press, Cardiff, United Kingdom.
12 - Kolenbrander, P. E. 1997. Oral microbiology and coaggregation. In J. A. Shapiro and M. Dworkin (ed.), Bacteria as multicellular organisms, p. 245-269. Oxford University Press, Oxford, United Kingdom.
13 - Kolenbrander, P. E., and J. London. 1993. Adhere today, here tomorrow: oral bacterial adherence. J. Appl. Bacteriol. 175:3247-3252.
14 - Kolenbrander, P. E., K. D. Parrish, R. N. Andersen, and E. P. Greenberg. 1995. Intergeneric coaggregation of oral Treponema spp. with Fusobacterium spp. and intrageneric coaggregation among Fusobacterium spp. Infect. Immun. 63:4584-4588.[Abstract]
15 - Page, R. D. 1996. TreeView: an application to display phylogenetic trees on personal computers. Comput. Appl. Biosci. 12:357-358.[Free Full Text]
16 - Rainey, P. B., E. R. Moxon, and I. P. Thompson. 1993. Intraclonal polymorphism in bacteria, p. 263-300. In J. Gwynfryn Jones (ed.), Advances in microbial ecology. Plenum Press, New York, N.Y.
17 - Reasoner, D. J., and E. E. Geldrich. 1985. A new medium for the enumeration and subculture of bacteria from potable water. Appl. Environ. Microbiol. 49:1-7.[Abstract/Free Full Text]
18 - Rickard, A. H. 2001. Coaggregation between aquatic biofilm bacteria. Ph.D thesis. University of Manchester, Manchester, United Kingdom.
19 - Rickard, A. H., S. A. Leach, C. M. Buswell, N. J. High, and P. S Handley. 2000. Coaggregation between aquatic bacteria is mediated by specific-growth-phase-dependent lectin-saccharide interactions. Appl. Environ. Microbiol. 66:431-434.[Abstract/Free Full Text]
20 - Rickard, A. H., J. Thomas, S. A. Leach, C. M. Buswell, N. J. High, and P. S. Handley. 1999. Coaggregation amongst aquatic and oral bacteria is mediated by lectin-saccharide interactions, p. 343-354. In J. Wimpenny, P. Gilbert, J. Walker, M. Brading, and R. Bayston (ed.), Biofilms: the good, the bad and the ugly. Bioline press, Cardiff, United Kingdom.
21 - Thompson, J. D., T. J. Gibson, F. Plewniak, F. Jeanmougin, and D. G. Higgins. 1997. The CLUSTAL X windows interface: flexible strategies for multiple sequence alignment aided by quality analysis tools. Nucleic Acids Res. 25:4876-4882.[Abstract/Free Full Text]
22 - Weisberg, W. G., S. M. Barns, D. A. Pelletier, and D. J. Lane. 1991. 16S Ribosomal DNA amplification for phylogenetic study. J. Bacteriol. 173:697-703.[Abstract/Free Full Text]
23 - Wilson, K. E., Blitchington, R. B., and R. C. Greene. 1990. Amplification of bacterial 16S ribosomal DNA with polymerase chain reaction. J. Clin. Microbiol. 28:1942-1946.[Abstract/Free Full Text]
Applied and Environmental Microbiology, July 2002, p. 3644-3650, Vol. 68, No. 7
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.7.3644-3650.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
This article has been cited by other articles:
-
Min, K. R., Rickard, A. H.
(2009). Coaggregation by the Freshwater Bacterium Sphingomonas natatoria Alters Dual-Species Biofilm Formation. Appl. Environ. Microbiol.
75: 3987-3997
[Abstract]
[Full Text]
-
Yang, C., Zhu, Y., Yang, J., Liu, Z., Qiao, C., Mulchandani, A., Chen, W.
(2008). Development of an Autofluorescent Whole-Cell Biocatalyst by Displaying Dual Functional Moieties on Escherichia coli Cell Surfaces and Construction of a Coculture with Organophosphate-Mineralizing Activity. Appl. Environ. Microbiol.
74: 7733-7739
[Abstract]
[Full Text]
-
Simoes, L. C., Simoes, M., Vieira, M. J.
(2008). Intergeneric Coaggregation among Drinking Water Bacteria: Evidence of a Role for Acinetobacter calcoaceticus as a Bridging Bacterium. Appl. Environ. Microbiol.
74: 1259-1263
[Abstract]
[Full Text]
-
Chu, K. H., Li, C. P., Qi, J.
(2006). Ribosomal RNA as molecular barcodes: a simple correlation analysis without sequence alignment. Bioinformatics
22: 1690-1701
[Abstract]
[Full Text]
-
Rickard, A. H., McBain, A. J., Stead, A. T., Gilbert, P.
(2004). Shear Rate Moderates Community Diversity in Freshwater Biofilms. Appl. Environ. Microbiol.
70: 7426-7435
[Abstract]
[Full Text]
-
Jiang, H.-L., Tay, J.-H., Maszenan, A. M., Tay, S. T.-L.
(2004). Bacterial Diversity and Function of Aerobic Granules Engineered in a Sequencing Batch Reactor for Phenol Degradation. Appl. Environ. Microbiol.
70: 6767-6775
[Abstract]
[Full Text]
-
Malik, A., Sakamoto, M., Hanazaki, S., Osawa, M., Suzuki, T., Tochigi, M., Kakii, K.
(2003). Coaggregation among Nonflocculating Bacteria Isolated from Activated Sludge. Appl. Environ. Microbiol.
69: 6056-6063
[Abstract]
[Full Text]
-
Grossart, H.-P., Kiorboe, T., Tang, K., Ploug, H.
(2003). Bacterial Colonization of Particles: Growth and Interactions. Appl. Environ. Microbiol.
69: 3500-3509
[Abstract]
[Full Text]
-
Palmer, R. J. Jr., Gordon, S. M., Cisar, J. O., Kolenbrander, P. E.
(2003). Coaggregation-Mediated Interactions of Streptococci and Actinomyces Detected in Initial Human Dental Plaque. J. Bacteriol.
185: 3400-3409
[Abstract]
[Full Text]
-
Foster, J. S., Palmer, R. J. Jr., Kolenbrander, P. E.
(2003). Human Oral Cavity as a Model for the Study of Genome-Genome Interactions. Biol. Bull.
204: 200-204
[Abstract]
[Full Text]