Hopanoids are pentacyclic triterpenoids sterol-like membrane lipids which are one of the widespread of all complex natural products. They have great significance in geological records and are found in phylogenetically diverse bacteria. Hopanoids can be used as the molecular fossils and were reported from the ancient sediments, modern sediments, fossil records, petroleum reservoir, Archean and Proterozoic rocks. Till date studies have mainly focused on geological significance of hopanoids whereas in last decade have addressed specially towards hopanoid biosynthetic pathway and role of hopanoids in bacteria. This review consists of general introduction of hopanoids, hopanoid biosynthetic pathway and role of hopanoids with future prospective.
Till today 366 bacteria which represent 206 species, 117 genera and 10 major phyla were screened for hopanoids and it was observed that the distribution of hopanoid is heterogeneous among the screened bacteria. Screenings of genomes have revealed that only 10.5% of sequenced organisms have genetic capacity to synthesize pentacyclic triterpenoid of hopane series. Hopanoids are involved in antibiotic resistance, tolerance to stress; nutrient storage enhances membrane stability and decreases membrane permeability. Hopanoid interacts with lipid A and contribute to membrane fluidity and lipid packing.
?hpnH and ?hpnP mutant of Bradyrhizobium diazoefficienshas shown defective plant microbe interaction and mislocalization of hopanoid shows defective cell cycle. There is correlation between the function of hopanoids and secretion of cellulose in Methylobacterium sp. Few studies have reported that the exposure to hopane hydrocarbon along with particulate matter leads to asthma disease, ischemis heart diseases, cardiac dysrhythmia, congestive heart failure and shortness of breath. However, the role of hopanoids is not conclusively elucidated and the extent to which they are sterol surrogate remains an open question. Therefore, a robust interpretation of phylogenetic distribution and cellular function of hopanoid is required to better understand their physiological significance