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. 

What are microbial mats?

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).

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