In order to balance the desire to maximize the number and diversity of strains to the user community while maintaining the quality of the existing Collection with its limited resources, it is necessary to define criteria for accepting new strains into the UTEX Collection. The criteria listed below are used as a guide to determine which new strains to incorporate, and which lost strains to replace. However, it is impossible to apply these criteria quantitatively since each individual strain has its own unique attributes whose value must be considered.
An algal strain can only be accepted for inclusion into the permanent UTEX Collection if it:
The following sequence of events is followed in accessing a new strain for inclusion into the Culture Collection of Algae at The University of Texas.
No simple definition can be applied to all organisms that are generally recognized as algae while excluding all organisms that do not appear to be algae. A loose and rather widely recognized definition is as follows: Algae are oxygenic photosynthetic organisms that do not possess a highly differentiated vascular system nor multicellular sterile tissues surrounding their gametes. Stated in slightly expanded form, they are typified by the following characters:
This description distinguishes algae from most plants, animals, fungi, nonphotosynthetic protists and nonoxygenic prokaryotes. It is a practical definition for many ecological and physiological considerations, and is convenient for broad taxonomic identifications. Yet, it has very little phylogenic (evolutionary) relevance.
The Culture Collection of Algae at the University of Texas at Austin (UTEX) generally adheres to the loose definition given above in determining which strains of living organisms are appropriate to maintain in the Collection. However, a few strains in the Collection fall outside of these boundaries. For example, certain colorless, nonphotosynthetic strains are so similar morphologically and genetically to typical algae that they are universally recognized as belonging to the algae.
The algae fall into two broad categories: cyanobacteria and eukaryotic algae. The cyanobacteria (also called blue-green algae, blue-green bacteria, chloroxybacteria or cyanophytes) are prokaryotic organisms. The eukaryotic algae represent an extremely diverse assemblage of organisms that do not form a coherent phylogenetic group (i.e. they are not monophyletic).
Traditionally the algae have been classified according to the rules of botanical nomenclature. Accordingly, the primary groupings are designated as "divisions", secondary groupings as "classes", etc. This system is impractical for prokaryotes and has become virtually intractable for protists (including algae) since the organisms associated with these traditional categories do not form well-defined phylogenetic groups. Most traditional divisions of eukaryotic algae are more closely related to major groups of non-algal protists than to any other algal division. Modern methods of phylogenetic analysis, especially DNA sequence data, are continually altering the ways that algae are classified.
Names and inferred phylogenetic relationships at practically every taxonomic level are in flux for most algal taxa. Thus, it may be impossible to assign names that remain valid over time, or that will be universally accepted even at the time they are assigned. For that reason UTEX does not attempt to determine the most recently assigned names for strains in the Collection. A new strain is accessioned into the Collection only when there is reason to believe that the depositor has correctly identified the strain and designated it with an accurate name based on information available at the time of deposition. The strain is then accessioned under that name. The accession name, along with its corresponding accession number, remains with the strain as long as it is maintained in continuous culture. UTEX personnel do not actively search the literature for revised names, but when UTEX personnel become aware of a name change for a UTEX strain recommended by an established expert, then the new name, along with a reference to the published manuscript describing the change, will be included in the list of cultures. The new name will be listed alphabetically by genus and specific epithet, designated as "a.k.a." and cross-referenced to the accession name. The a.k.a. (aka-nym) designation means that the name is believed correspond to the strain in the Collection listed under a different accessioning name.
A unique accession number is assigned to each separate isolate accessioned into the Collection. Thus, no two isolates in UTEX are ever assigned the same number, and no isolate is assigned more than one number. Even when an accessioned strain has been lost for many years, its accession number is not re-assigned to a different isolate.
On occasion a strain that previously had been accessioned is lost. Under most circumstances the accession number is then retired, and is never used again for a UTEX strain. Any other accessioned isolate, even it is appears identical to the lost strain and is isolated from the same location as was the lost strain, is assigned a different accession number.
When the same isolate prepared as a unialgal culture is deposited in UTEX and also in another collection, then a replacement culture may be requested from the other collection if the strain is lost to UTEX. Under this circumstance the acquired culture will be assigned the same accession number as the culture originally deposited in UTEX. The primary name of the strain will be assigned the name under which it is listed in the other collection, which may not be the same as the name of under which the strain was first accessioned by UTEX.
Only unialgal strains are accessioned into the collection, and only when identified and named by an established authority. UTEX makes no guarantee regarding the correct and most recent names of strains held in the Collection. Nor do UTEX personnel systematically examine strains in the Collection to assure their correct taxonomic identity.
In order to maintain healthy cultures many hundreds of algal transfers are made every month. Although internal checks eliminate nearly all mistakes, on rare occasion a culture is mislabeled or is contaminated with another strain. Any culture that appears to be mislabeled is immediately discarded. Cultures of uncertain strain identity are discarded even if that means the permanent loss of an accessioned UTEX strain.