Growth of elaborate microbial pinnacles in Lake Vanda, Antarctica

Abstract

Microbial pinnacles in ice-covered Lake Vanda, McMurdo Dry Valleys, Antarctica, extend from the base of the ice to more than 50 m water depth. The distribution of microbial communities, their photosynthetic potential, and pinnacle morphology affects the local accumulation of biomass, which in turn shapes pinnacle morphology. This feedback, plus environmental stability, promotes the growth of elaborate microbial structures. In Lake Vanda, all mats sampled from greater than 10 m water depth contained pinnacles with a gradation in size from <1-mm-tall tufts to pinnacles that were centimeters tall. Small pinnacles were cuspate, whereas larger ones had variable morphology. The largest pinnacles were up to ~30 cm tall and had cylindrical bases and cuspate tops. Pinnacle biomass was dominated by cyanobacteria from the morphological and genomic groups Leptolyngbya, Phormidium, and Tychonema. The photosynthetic potential of these cyanobacterial communities was high to depths of several millimeters into the mat based on PAM fluorometry, and sufficient light for photosynthesis penetrated ~5 mm into pinnacles. The distribution of photosynthetic potential and its correlation to pinnacle morphology suggests a working model for pinnacle growth. First, small tufts initiate from random irregularities in prostrate mat. Some tufts grow into pinnacles over the course of ~3 years. As pinnacles increase in size and age, their interiors become colonized by a more diverse community of cyanobacteria with high photosynthetic potential. Biomass accumulation within this subsurface community causes pinnacles to swell, expanding laminae thickness and creating distinctive cylindrical bases and cuspate tops. This change in shape suggests that pinnacle morphology emerges from a specific distribution of biomass accumulation that depends on multiple microbial communities fixing carbon in different parts of pinnacles. Similarly, complex patterns of biomass accumulation may be reflected in the morphology of elaborate ancient stromatolites.

Bacteriohopanepolyols across environmental gradients in Lake Vanda, Antarctica

“…Map of the McMurdo Dry Valleys, Antarctica, including Lake Vanda (adapted from Sumner et al., ). Red circle indicates approximate sampling locality [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Shade‐adapted benthic microbial mats dominated by cyanobacteria are responsible for the majority of primary production in Lake Vanda (Hawes & Schwarz, ; Quesada et al., ; Zhang et al., ). Microbial communities are organized within pinnacles and prostrate mats (Hawes & Schwarz, ; Hawes et al., ; Sumner et al., ), contributing to the development of and exploiting steep environmental gradients. For example, the mats are finely laminated and contain characteristic pigmented zones (from orange to green and purple) that reflect acclimation to changing spectral characteristics with depth into the mats through the synthesis of particular pigments (from carotenoids to phycocyanin and phycoerythrin; Hawes et al., ).…”

Depositional setting of the 2·1 Ga Francevillian macrobiota (Gabon): Rapid mud settling in a shallow basin swept by high‐density sand flows

“…Motile filaments may promote gliding and tangling of the mat (Shepard & Sumner, ). Importantly, tuft filamentous structures similar to those formed by cyanobacteria in modern environments (Gerdes et al ., ; and Gerdes, ; Bose & Chafetz, ; Taj et al ., ; Sumner et al ., ) are found either within the mat (Fig. E) or at the ridge junctions of the elephant skin textures or reticulate patterns.…”

“…So far, modern occurrences of tufts and tuft‐related structures have been assigned to oxygen‐producing photosynthetic bacteria (Walter et al ., ; Bosak et al ., , ; Reyes et al ., ; Jungblut et al ., ; Sumner et al ., ). In the Francevillian mats, some void clusters could be related to photosynthetic, degassing structures similar to those illustrated by Eriksson et al .…”

Microbial carbonation in natural and engineered environments

“…Studying microbial carbonation in dissimilar environments provides an opportunity to appreciate the ubiquitous nature of this biogeochemical process. It occurs in fresh and salt water environments, in aquatic and terrestrial habitats, and in polar and tropical climates Andersen et al, 2011;Braissant et al, 2003;Dittrich et al, 2003;Gerard et al, 2013;Mackey et al, 2015;Sumner et al, 2016;. As a subset of this range of possibilities, the Heron Island beachrock represents a natural tropical marine environment that, due to its intertidal nature, is both aquatic and terrestrial, and hosts microbial calcium carbonate mineral precipitation.…”