Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal Study of soil cyanobacteria along a rural-urban gradient Pradeep Kumar Rai a , Anuradha Rai a , Naveen Kumar Sharma b , Surendra Singh a, ⁎ a Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi 221005, India b Department of Botany, Indira Gandhi National Tribal University, Amarkantak, Madhya Pradesh 484 887, India ARTICLE INFO Keywords: Urbanization Cyanobacteria 16S rRNA Morphology Phylogeny ABSTRACT Urbanization is one of the modern and critical factors adversely affecting global biodiversity. The impact of urbanization on soil microbial diversity has sporadically been studied of cyanobacterial diversity. The present study analyzes morphological as well as molecular diversity of cyanobacteria along a rural-urban gradient using a culture based approach. In total, 22 cyanobacterial morphotypes (14 genera and 21 species) from five orders were reported; dominated by the members of the order Nostocales. In general, cyanobacterial diversity de- creased from rural to urban areas; with N 2 -fixing heterocystous forms dominating the cyanobacterial flora of the urban area. The values of Shannon–Weaver (2.56) and Simpson's (2.32) indices suggested higher cyanobacterial diversity in the rural area compared to that of the sub-urban and urban areas. Statistical analyses established the importance of physico-chemical factors in structuring the cyanobcaterial communities along the gradient with soil characteristics such as – pH, organic carbon, nitrogen and bulk density, directly as well as indirectly. 1. Introduction The Millennium Ecosystem Assessment report [1] suggests that during the past 60 years, land cover change has resulted in severe global terrestrial biodiversity loss. Among various factors, advancing urbanization has been responsible for extensive modifications of the landscape. Urbanization alters the quality of air, water and soil, tem- perature regime and rainfall patterns of the environments, which could lead to the destruction and fragmentation of the natural habitats and protuberances in biological communities [2–4], thereby, possing a major threat to the biodiversity. McDonnell et al. [5] proposed the concept of rural-urban-gradient to model the ecological effects of ur- banization on soil-biological systems. Besides variations in several physico-chemical parameters, such gradients differ in the amount of built-up area (buildings, roads and asphalt covered paths) and differ- ences in the habitat maintenance operations. The length of the selected gradient/transect vary depending upon the kind of organism/group is to be studied. A greater length of transect is required for the study of macrophytes compared to their microbial counterparts, with basic rock composition remaining similar along the gradient. Due to their high diversity and abundance, microorganisms con- stitute a bulk of soil genetic resource [6,7]. Soil microbes play a crucial role in the functioning of soil ecosystems directly through cycling of soil nutrients, decomposition of soil organic matter, detoxification of pol- lutants, and indirectly as a crucial regulator of global climate. However, soil microbial population and associated ecosystems services are sen- sitive to changes in external conditions imposed by land use mod- ifications and human management practices (i.e., urbanization, agri- cultural intensification and industrialization, etc.) [7–9]. Studies suggest that urbanization has profoundly impacted the function and composition of soil microbial communities [10–12]. The resulting change could be used for evaluating the soil and ecosystem function. However, due to methodological limitations and site specificity, often factors affecting the structure and functioning of soil microbial com- munities (i.e., abundance, spatial organization, etc.) are not clearly understood [13], which limits our understanding of the role of soil microbial diversity in ecosystem services [14]. Information is mainly available on the diversity of plants, arthropods, fungi, bacteria, along the urbanization gradient. Cyanobacteria (also known as Blue-green algae), is a morphologi- cally diverse group of photooxybacteria, with worldwide distribution in diverse ecosystems. They represent one of the major eubacterial groups and possess unique characteristics of oxygenic photosynthesis and N 2 - fixation among the prokaryotes. In soil, they provide fixed nitrogen and photosynthetically fixed carbon to plants and other soil components [15,16]. In addition, they play an important role in ecosystem function, such as stabilization of soil or mobilization of sand surfaces by excretion of extracellular polysaccharides, hinder wind erosion and facilitate the initial establishment of higher plants and subsequent feedback me- chanisms [17–20]. In recent times, they have emerged as a valuable https://doi.org/10.1016/j.algal.2018.08.032 Received 29 March 2018; Received in revised form 23 August 2018; Accepted 23 August 2018 ⁎ Corresponding author at: Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi, UP 221005, India. E-mail address: pkrai17@gmail.com (S. Singh). Algal Research 35 (2018) 142–151 2211-9264/ © 2018 Elsevier B.V. All rights reserved. T