Unusual Crystal Formation in Organisms - Exceptions that Confirm Biomineralization Rules

Biomineralization is a complex combination of biochemical and physiological processes, depending on endogenous activity of an organism and the exogenous environmental influence. In marine organisms (bacteria, calcareous algae, molluscs, crustaceans, fish and mammals) biomineralization starts at early stages of development and continues during the entire life. These processes take place in different tissues, shells and skeletons, and are manifested in calcification, decalcification and in polymorph transitions of calcium carbonate in particular shell or skeleton layers (Lowenstam, 1981 ; McConnaughey, 1989). Biomineralization processes depend on a number of conditions of which the main ones, that influence the type and structure of the biomineral, are the following: supersaturation of the medium with calcium and other ions, the nature of the critical nucleus, characteristics of the organic matrix, promotors and inhibitors of phase transitions, environmental temperature, salinity concentration and pH ranges (Wilbur & Saleuddin, 1983 ; Addadi & Weiner, 1992 ; Mann, 1991, 2001 ; Bauerlein, 2004 ; Veis, 2008). The research related to the biomineralization processes is interdisciplinary and the main aim of the present review is to express and interpret results obtained by different methods and approaches. In this review we address three major topics. First, we turn back to the period before the modern-biomineralization theory, which presents several innovative hypotheses and proposes mechanisms fundamental in understanding crystal formation in the living organisms. These advanced ideas were randomly or deliberately neglected and minimized in recent biomineralization literature, and they deserve attention. Next, we take up the role of different research methodologies that directly promote and address some of the pressing profiles in explanation or acceptance of unusual-usual biomineralization processes. Third, we turn to areas that require a closer attention and a more intense effort in presenting the recent synthesis and generalization of the mineralization of the organisms. One of these is well confirmed and accepted knowledge and techniques underlying the environmentally induced biomineralization and the influence of different extrinsic conditions on crystal formation in adult invertebrates. The area is apparently much intricate and faces increasing difficulty in well-trained understanding of the biomineralization related to starting-initial biomineralization processes, the first crystals formation and growth during early embryogenesis up to the juvenile and adult organisms. Major achievements and examples of fundamental results in recent years will be presented. It depends of the personal scientific judgement whether the distinction between the basic mechanisms of the initial crystal formation and evolutionary role of these processes on the general aspects of the biomineralization represents a real difference.