Correlation of carotenoid accumulation with aggregation and biofilm development in Rhodococcus sp. SD-74.

Aggregation of bacterial populations substantially influences their characteristic properties and functions compared with the planktonic counterpart. It is also involved in the initial stages of biofilm development. Many studies have revealed important roles of bacterial aggregation in microbial production and biodegradation. Nevertheless, mechanistic understanding of bacterial aggregation in vivo and at the molecular level is far from complete. Here, we present a noninvasive, label-free Raman microspectroscopic approach to investigate the aggregation and biofilm development of the biotechnologically important Rhodococcus sp. SD-74. We found that the concentration of intracellular carotenoids increases more than 3-fold within 1 week as the biofilm develops. Raman imaging experiments confirmed that the carotenoid accumulation occurs throughout the Rhodococcus sp. SD-74 biofilm. The correlation between the carotenoid Raman intensities and biofilm development found in the present study provides a new means for quantitative, molecular-level assessment of the level of biofilm development, which is not possible with dye staining assay or electron microscopy. Moreover, our results suggest that microbial production of carotenoids in pigmented bacteria such as Rhodococcus sp. SD-74 may potentially be controlled via bacterial aggregation and biofilm formation.