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Cabo Rojo Salterns Microbial Observatory

University of Puerto Rico at Humacao

   

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Research

 

Main research goals

 

1. Determine changes in physicochemical conditions

during seasons.

 

2. Enrich for moderate and extreme halophiles.

 

3. Cultivation of novel organisms from the salt ponds and sediments around the ponds.

 

To better understand geomicrobiological processes our approach encompasses a combination of geochemical, geological, microbial and molecular techniques.

 

Publications

 

Hernández-Machado B., and Casillas, L. (2009). Design and Assessment of an Introductory Geomicrobiology Course for Non-Geology Majors. Journal of Geoscience Education. p.p. 23-32. PDF

 

Isenbarger, T.A., Finney, M.Ríos-Velázquez, C. et al. (2008). Miniprimer PCR, a New Lens for Viewing the Microbial World. Applied and Environmental Microbiology. p.p. 840-849. PDF

 

Ríos-Velázquez, C. et al.  (2007).  Learning Geomicrobiology as a Team Using Microbial Mats, a Multidisciplinary Approach.  Journal of Microbiology & Biology Education. p.p. 28-35. PDF

 

Cantrell, S.A. et al. (2007). Periconia variicolor sp.nov., a new species from Puerto Rico. Mycologia, 99(3), pp. 482-487. PDF

 

Cantrell, S.A. et al. (2006). Characterization of fungi from hypersaline environments of solar salterns using morphological and molecular techniques. Micological Research 110. p. 962-970. PDF

 

Casillas-Martinez, L. et al.  (2005).  Community Structure, Geochemical Characteristics and Mineralogy of a Hypersaline Microbial Mat, Cabo Rojo, PR. Geomicrobiology Journal, 22:269-281. PDF

 

 

 

Physicochemical Conditions

 

Salinity in the Cabo Rojo salt ponds increase as the incoming water moves from pond to pond with values up to 520 practical salinity units (PSU).  Using needle microelectrodes we determined the oxygen profiles of pond A (click rectangle to see) .

 

Oxygen penetrated 3 mm deep into the water column throughout an area of active precipitation in the salt crust of the bottom.  Further physicochemical analysis of these ponds indicate a large concentration of commonly limiting nutrients such as phosphorus and nitrogen.  The presence of  NO3 could result from nitrification activity and the low sulfate concentrations in the water column are possibly due to the precipitation of  BaSO4 and CaSO4  2H2O.

Microelectrodes

 

 

Shallow oxygen penetration in the Cabo Rojo salterns was measured by the use of needle electrodes.  Click here for a schematic cross section of the oxygen electrode used in our study.

 

Microorganisms in the Salterns are Subjected to Extreme Seasonal Changes

 

Seasonal variations in precipitation changed the community composition and microbial activity in a hypersaline, tropical microbial mat, in Cabo Rojo, PR.  Using a combination of dissection, light, transmission and scanning electron microscopy, terminal restriction fragment length polymorphism (T-RFLP), in situ microelectrode studies, and 35S isotope incubations, we documented the major differences between dry and wet seasons. 

 

  Dry

Wet

Presc. (in) 2 7
Temp (°C) 33 26
Salinity (ppt) 150-256 40-150
pH 8.25 7.95

What are microbial mats?

 

Microbial mats are laminated ecosystems within the soil composed of different microbial communities.  They are typically dominated by cyanobacteria. 

 

 

As shown in the picture above, the microbial mats around the Cabo Rojo salterns present colored bands (green, pink or cream and black) characteristics for cyanobacterial-dominated systems.

Enrichment of Halophiles

 

The salt ponds and the sediments around the Cabo Rojo Salterns are convenient systems to study how biochemical changes through all salinity gradients might be responsible for the enrichments of different halophiles. Using selective plates for moderate and extreme halophiles we culture a

large variety of organisms (see table 1).

 

Table 1: Colony forming units per ml of filtered pond water counted after

an incubation period of 2 months. TMTC = too many to count.
 

 
MH-5 plate

LA-25 plate

 


Bacterial Counts
(CFU x ml)
Inlet Pond 1 Pond 2 Pond 3 Pond 4
MH 5 2 2 1 2 2
MH 10 49 35 11 8 1
MH 15 TMTC TMTC TMTC TMTC TMTC
MH 20 TMTC 109 TMTC TMTC TMTC
LA 25 7 5 6 10 TMTC
LA 30 15 10 25 14 5
LA >30 2 12 1 2 5

  
Table 2: Organisms identified in the salt ponds of the Cabo Rojo solar salterns.

 

Closest relative
% of relativeness
Method of identification
Bacillus subtilis
88
Biochemical
Bacillus licheniformis
93
Biochemical
Bacillus sphaericus
99
Biochemical 
Bacillus subtilis
99
Biochemical 
Staphylococcus captitis
89
Biochemical
Bacillus licheniformis
98

Phylogenetic

Staphylococcus arletae  
96
Phylogenetic
Rhodospirillum salinarum
100
Phylogenetic
Aspergillus caesiellus
98
Phylogenetic
 

Cyanobacterial Mats

 

The cyanobacterial mats adjacent to the salterns include intertidal Microcoleus/Lynbya-dominated systems. Spirulina, Synechococcus, Apanothece and Phormidium can also be found. A pronounced layer of Ectothiorhodospira spp. and an abundant population of sulfate-reducing bacteria are also present. These mats are subject to drastic changes during the dry and rainy seasons.  During the dry period a salt crust (Figures 1 and 2) of several mm of thickness cover the mats which are able to  recover during the rainy season (figures 3 and 4).  Our students are currently studying changes in the environmental conditions such as temperature, light and pH and how them affect the communities within these mats (Figure 5).

 

1  2   4 5
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Web page designed by Beatriz Hernández Machado

Updated by Ángel Casanova

Last revision May 2010