Spectacular examples of highly visible microbial communities are living in the lavatubes of the world (Howarth, 1981; Northup & Welbourn, 1997; Northup et al., 2004, 2008; Staley & Crawford, 1975). Very little is known about the nature of these colorful microbial communities but some scientists are turning their attentions to these amazing and beautiful microorganisms (Ashmole et al., 1992, Lazzarini et al., 2000, Northup et al. 2008). Most lava tubes with any moisture have visible and abundant white microbial mats. At certain times of the year, water beads up on the mats due to their hydrophobicity (repellance to water), giving the lava tube walls the appearance of being silvered. Other lava tubes are coated in glittering gold, pink or orange colonies looking as if they were lined in sequins. Such microbial coatings can cover 25-75% of the wall surfaces. Experimental vacuuming of bacterial mats in the dark zone and the adjacent algae in the partially lit twilight zone nearby recovered a variety of invertebrates on the algae (collembola and mites) but no invertebrates were recovered from the bacterial mats, suggesting that the bacteria may be unpalatable to arthropods, perhaps purposefully to discouraging grazing of the microbial biomass (Northup et al., 2004).
The appearance of many of these lavatube microbial colonies under the microscope suggests that are probably composed of Actinobacteria, bacteria that commonly inhabit caves and that are known for their antibiotic production. Studies of bacterial genetic sequences of DNA extracted from New Mexican and Hawaiian lava tube mats suggests that Actinobacteria are present and often predominate in the microbial mats (Northup et al., 2004, 2008).
Some of the lava tube bacteria are much more UV sensitive than the microbes isolated from the surface (Boston, unpub. data), suggesting some degree of cave adaptation as has been reported for other types of caves (Snider et al., 2008). Lava tube microbial mats represent a rich source of novel bacteria with which to continue to explore the tree of life and provide opportunities to study what controls species diversity and antibiotic production in caves. Cave microorganisms may be partly derived from surface populations, especially caves with significant influx of water or other surface materials. However, the unique sets of conditions experienced in lavatubes or other caves sets the stage for separate evolutionary developments of organisms adapted to those environments.